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From: "Jørgen Kvalsvik" <jorgen.kvalsvik@woven-planet.global>
To: gcc-patches@gcc.gnu.org
Cc: mliska@suse.cz, "Jørgen Kvalsvik" <jorgen.kvalsvik@woven-planet.global>
Subject: [PATCH v3] Add condition coverage profiling
Date: Mon,  5 Dec 2022 10:40:38 +0900	[thread overview]
Message-ID: <20221205014037.94341-1-jorgen.kvalsvik@woven-planet.global> (raw)

This patch adds support in gcc+gcov for modified condition/decision
coverage (MC/DC) with the -fprofile-conditions flag. MC/DC is a type of
test/code coverage and it is particularly important in the avation and
automotive industries for safety-critical applications. MC/DC it is
required for or recommended by:

    * DO-178C for the most critical software (Level A) in avionics
    * IEC 61508 for SIL 4
    * ISO 26262-6 for ASIL D

 From the SQLite webpage:

    Two methods of measuring test coverage were described above:
    "statement" and "branch" coverage. There are many other test
    coverage metrics besides these two. Another popular metric is
    "Modified Condition/Decision Coverage" or MC/DC. Wikipedia defines
    MC/DC as follows:

        * Each decision tries every possible outcome.
        * Each condition in a decision takes on every possible outcome.
        * Each entry and exit point is invoked.
        * Each condition in a decision is shown to independently affect
          the outcome of the decision.

    In the C programming language where && and || are "short-circuit"
    operators, MC/DC and branch coverage are very nearly the same thing.
    The primary difference is in boolean vector tests. One can test for
    any of several bits in bit-vector and still obtain 100% branch test
    coverage even though the second element of MC/DC - the requirement
    that each condition in a decision take on every possible outcome -
    might not be satisfied.

    https://sqlite.org/testing.html#mcdc

Wahlen, Heimdahl, and De Silva "Efficient Test Coverage Measurement for
MC/DC" describes an algorithm for adding instrumentation by carrying
over information from the AST, but my algorithm analyses the the control
flow graph to instrument for coverage. This has the benefit of being
programming language independent and faithful to compiler decisions
and transformations, although I have only tested it on constructs in C
and C++, see testsuite/gcc.misc-tests and testsuite/g++.dg.

Like Wahlen et al this implementation records coverage in fixed-size
bitsets which gcov knows how to interpret. This is very fast, but
introduces a limit on the number of terms in a single boolean
expression, the number of bits in a gcov_unsigned_type (which is
typedef'd to uint64_t), so for most practical purposes this would be
acceptable. This limitation is in the implementation and not the
algorithm, so support for more conditions can be added by also
introducing arbitrary-sized bitsets.

For space overhead, the instrumentation needs two accumulators
(gcov_unsigned_type) per condition in the program which will be written
to the gcov file. In addition, every function gets a pair of local
accumulators, but these accmulators are reused between conditions in the
same function.

For time overhead, there is a zeroing of the local accumulators for
every condition and one or two bitwise operation on every edge taken in
the an expression.

In action it looks pretty similar to the branch coverage. The -g short
opt carries no significance, but was chosen because it was an available
option with the upper-case free too.

gcov --conditions:

        3:   17:void fn (int a, int b, int c, int d) {
        3:   18:    if ((a && (b || c)) && d)
condition outcomes covered 3/8
condition  0 not covered (true false)
condition  1 not covered (true)
condition  2 not covered (true)
condition  3 not covered (true)
        1:   19:        x = 1;
        -:   20:    else
        2:   21:        x = 2;
        3:   22:}

gcov --conditions --json-format:

    "conditions": [
        {
            "not_covered_false": [
                0
            ],
            "count": 8,
            "covered": 3,
            "not_covered_true": [
                0,
                1,
                2,
                3
            ]
        }
    ],

Some expressions, mostly those without else-blocks, are effectively
"rewritten" in the CFG construction making the algorithm unable to
distinguish them:

and.c:

    if (a && b && c)
        x = 1;

ifs.c:

    if (a)
        if (b)
            if (c)
                x = 1;

gcc will build the same graph for both these programs, and gcov will
report boths as 3-term expressions. It is vital that it is not
interpreted the other way around (which is consistent with the shape of
the graph) because otherwise the masking would be wrong for the and.c
program which is a more severe error. While surprising, users would
probably expect some minor rewriting of semantically-identical
expressions.

and.c.gcov:
    #####:    2:    if (a && b && c)
condition outcomes covered 6/6
    #####:    3:        x = 1;

ifs.c.gcov:
    #####:    2:    if (a)
    #####:    3:        if (b)
    #####:    4:            if (c)
    #####:    5:                x = 1;
condition outcomes covered 6/6

Adding else clauses alters the program (ifs.c can have 3 elses, and.c
only 1) and coverage becomes less surprising

ifs.c.gcov:
    #####:    2:    if (a)
condition outcomes covered 2/2
    #####:    4:    {
    #####:    4:        if (b)
condition outcomes covered 2/2
              5:        {
    #####:    6:            if (c)
condition outcomes covered 2/2
    #####:    7:                x = 1;
    #####:    8:        }
    #####:    9:        else
    #####:   10:            x = 2;
    #####:   11:    }
    #####:   12:    else
    #####:   13:        x = 3;

Since the algorithm works on CFGs, it cannot detect some ternary
operator introduced conditionals. For example, int x = a ? 0 : 1 in
gimple becomes _x = (_a == 0). From source you would expect coverage,
but it gets neither branch nor condition coverage. For completeness, it
could be achieved by scanning all gimple statements for such
comparisons, and insert an extra instruction for recording the outcome.

The test suite contains a lot of small programs functions. Some of these
were designed by hand to test for specific behaviours and graph shapes,
and some are previously-failed test cases in other programs adapted into
the test suite.

Alternative author email: Jørgen Kvalsvik <j@lambda.is>

gcc/ChangeLog:

	* builtins.cc (expand_builtin_fork_or_exec): Check
	profile_condition_flag.
	* collect2.cc (main): Add -fno-profile-conditions to OBSTACK.
	* common.opt: Add new options -fprofile-conditions and
	* doc/gcov.texi: Add --conditions documentation.
	* doc/invoke.texi: Add -fprofile-conditions documentation.
	* gcc.cc: Link gcov on -fprofile-conditions.
	* gcov-counter.def (GCOV_COUNTER_CONDS): New.
	* gcov-dump.cc (tag_conditions): New.
	* gcov-io.h (GCOV_TAG_CONDS): New.
	(GCOV_TAG_CONDS_LENGTH): Likewise.
	(GCOV_TAG_CONDS_NUM): Likewise.
	* gcov.cc (class condition_info): New.
	(condition_info::condition_info): New.
	(condition_info::popcount): New.
	(struct coverage_info): New.
	(add_condition_counts): New.
	(output_conditions): New.
	(print_usage): Add -g, --conditions.
	(process_args): Likewise.
	(output_intermediate_json_line): Output conditions.
	(read_graph_file): Read conditions counters.
	(read_count_file): Read conditions counters.
	(file_summary): Print conditions.
	(accumulate_line_info): Accumulate conditions.
	(output_line_details): Print conditions.
	* ipa-inline.cc (can_early_inline_edge_p): Check
	profile_condition_flag.
	* ipa-split.cc (pass_split_functions::gate): Likewise.
	* passes.cc (finish_optimization_passes): Likewise.
	* profile.cc (find_conditions): New declaration.
	(cov_length): Likewise.
	(cov_blocks): Likewise.
	(cov_masks): Likewise.
	(cov_free): Likewise.
	(instrument_decisions): New.
	(read_thunk_profile): Control output to file.
	(branch_prob): Call find_conditions, instrument_decisions.
	(init_branch_prob): Add total_num_conds.
	(end_branch_prob): Likewise.
	* tree-profile.cc (struct conds_ctx): New.
	(CONDITIONS_MAX_TERMS): New.
	(EDGE_CONDITION): New.
	(cmp_index_map): New.
	(index_of): New.
	(block_conditional_p): New.
	(edge_conditional_p): New.
	(single): New.
	(single_edge): New.
	(contract_edge): New.
	(contract_edge_up): New.
	(merge_split_outcome): New.
	(ancestors_of): New.
	(struct outcomes): New.
	(conditional_succs): New.
	(condition_index): New.
	(masking_vectors): New.
	(cond_reachable_from): New.
	(neighborhood): New.
	(isolate_expression): New.
	(emit_bitwise_op): New.
	(make_index_map_visit): New.
	(make_index_map): New.
	(collect_conditions): New.
	(yes): New.
	(struct condcov): New.
	(cov_length): New.
	(cov_blocks): New.
	(cov_masks): New.
	(cov_free): New.
	(find_conditions): New.
	(instrument_decisions): New.
	(tree_profiling): Check profile_condition_flag.
	(pass_ipa_tree_profile::gate): Likewise.

libgcc/ChangeLog:

	* libgcov-merge.c (__gcov_merge_ior): New dummy function.

gcc/testsuite/ChangeLog:

	* lib/gcov.exp: Add condition coverage test function.
	* g++.dg/gcov/gcov-18.C: New test.
	* gcc.misc-tests/gcov-19.c: New test.
	* gcc.misc-tests/gcov-20.c: New test.
	* gcc.misc-tests/gcov-21.c: New test.
---
v1 -> v2:
    * Moved the docs to rst/sphinx
    * Output and message uses the 'conditions outcomes' vocabulary
    * Fixed errors reported by contrib/style-check. Note that a few
      warnings persist but are either in comments (ascii art) or because
      the surrounding code (typically lists) are formatted the same way
v2 -> v3:
    * Revert docs from rst/sphinx to texinfo

 gcc/builtins.cc                        |    2 +-
 gcc/collect2.cc                        |    7 +-
 gcc/common.opt                         |    8 +
 gcc/doc/gcov.texi                      |   37 +
 gcc/doc/invoke.texi                    |   19 +
 gcc/gcc.cc                             |    4 +-
 gcc/gcov-counter.def                   |    3 +
 gcc/gcov-dump.cc                       |   24 +
 gcc/gcov-io.h                          |    3 +
 gcc/gcov.cc                            |  200 +++-
 gcc/ipa-inline.cc                      |    2 +-
 gcc/ipa-split.cc                       |    3 +-
 gcc/passes.cc                          |    3 +-
 gcc/profile.cc                         |   84 +-
 gcc/testsuite/g++.dg/gcov/gcov-18.C    |  234 +++++
 gcc/testsuite/gcc.misc-tests/gcov-19.c | 1250 ++++++++++++++++++++++++
 gcc/testsuite/gcc.misc-tests/gcov-20.c |   22 +
 gcc/testsuite/gcc.misc-tests/gcov-21.c |   16 +
 gcc/testsuite/lib/gcov.exp             |  191 +++-
 gcc/tree-profile.cc                    | 1048 +++++++++++++++++++-
 libgcc/libgcov-merge.c                 |    5 +
 21 files changed, 3137 insertions(+), 28 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/gcov/gcov-18.C
 create mode 100644 gcc/testsuite/gcc.misc-tests/gcov-19.c
 create mode 100644 gcc/testsuite/gcc.misc-tests/gcov-20.c
 create mode 100644 gcc/testsuite/gcc.misc-tests/gcov-21.c

diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 02c4fefa86f..8ce16bf9da4 100644
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -5889,7 +5889,7 @@ expand_builtin_fork_or_exec (tree fn, tree exp, rtx target, int ignore)
   tree call;
 
   /* If we are not profiling, just call the function.  */
-  if (!profile_arc_flag)
+  if (!profile_arc_flag && !profile_condition_flag)
     return NULL_RTX;
 
   /* Otherwise call the wrapper.  This should be equivalent for the rest of
diff --git a/gcc/collect2.cc b/gcc/collect2.cc
index d81c7f28f16..0cd8bf4a3a3 100644
--- a/gcc/collect2.cc
+++ b/gcc/collect2.cc
@@ -1032,9 +1032,9 @@ main (int argc, char **argv)
       lto_mode = LTO_MODE_LTO;
   }
 
-  /* -fno-profile-arcs -fno-test-coverage -fno-branch-probabilities
-     -fno-exceptions -w -fno-whole-program */
-  num_c_args += 6;
+  /* -fno-profile-arcs -fno-profile-conditions -fno-test-coverage
+     -fno-branch-probabilities -fno-exceptions -w -fno-whole-program */
+  num_c_args += 7;
 
   c_argv = XCNEWVEC (char *, num_c_args);
   c_ptr = CONST_CAST2 (const char **, char **, c_argv);
@@ -1230,6 +1230,7 @@ main (int argc, char **argv)
     }
   obstack_free (&temporary_obstack, temporary_firstobj);
   *c_ptr++ = "-fno-profile-arcs";
+  *c_ptr++ = "-fno-profile-conditions";
   *c_ptr++ = "-fno-test-coverage";
   *c_ptr++ = "-fno-branch-probabilities";
   *c_ptr++ = "-fno-exceptions";
diff --git a/gcc/common.opt b/gcc/common.opt
index 562d73d7f55..5542a304cb9 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -858,6 +858,10 @@ Wcoverage-invalid-line-number
 Common Var(warn_coverage_invalid_linenum) Init(1) Warning
 Warn in case a function ends earlier than it begins due to an invalid linenum macros.
 
+Wcoverage-too-many-conditions
+Common Var(warn_too_many_conditions) Init(1) Warning
+Warn when a conditional has too many terms and coverage gives up.
+
 Wmissing-profile
 Common Var(warn_missing_profile) Init(1) Warning
 Warn in case profiles in -fprofile-use do not exist.
@@ -2343,6 +2347,10 @@ fprofile-arcs
 Common Var(profile_arc_flag)
 Insert arc-based program profiling code.
 
+fprofile-conditions
+Common Var(profile_condition_flag)
+Insert condition coverage profiling code.
+
 fprofile-dir=
 Common Joined RejectNegative Var(profile_data_prefix)
 Set the top-level directory for storing the profile data.
diff --git a/gcc/doc/gcov.texi b/gcc/doc/gcov.texi
index a1f7d26e610..10c500645ff 100644
--- a/gcc/doc/gcov.texi
+++ b/gcc/doc/gcov.texi
@@ -124,6 +124,7 @@ gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}]
      [@option{-a}|@option{--all-blocks}]
      [@option{-b}|@option{--branch-probabilities}]
      [@option{-c}|@option{--branch-counts}]
+     [@option{-g}|@option{--conditions}]
      [@option{-d}|@option{--display-progress}]
      [@option{-f}|@option{--function-summaries}]
      [@option{-j}|@option{--json-format}]
@@ -169,6 +170,13 @@ be shown, unless the @option{-u} option is given.
 Write branch frequencies as the number of branches taken, rather than
 the percentage of branches taken.
 
+@item -g
+@itemx --conditions
+Write condition coverage to the output file, and write condition summary info
+to the standard output.  This option allows you to see if the conditions in
+your program at least once had an independent effect on the outcome of the
+boolean expression (modified condition/decision coverage).
+
 @item -d
 @itemx --display-progress
 Display the progress on the standard output.
@@ -293,6 +301,7 @@ Each @var{line} has the following form:
 @{
   "branches": ["$branch"],
   "count": 2,
+  "conditions": ["$condition"],
   "line_number": 15,
   "unexecuted_block": false,
   "function_name": "foo",
@@ -341,6 +350,34 @@ Fields of the @var{branch} element have following semantics:
 @var{throw}: true when the branch is an exceptional branch
 @end itemize
 
+Each @var{condition} has the following form:
+
+@smallexample
+@{
+  "count": 4,
+  "covered": 2,
+  "not_covered_false": [],
+  "not_covered_true": [0, 1],
+@}
+
+@end smallexample
+
+Fields of the @var{condition} element have following semantics:
+
+@itemize @bullet
+@item
+@var{count}: number of condition outcomes in this expression
+
+@item
+@var{covered}: number of covered condition outcomes in this expression
+
+@item
+@var{not_covered_true}: terms, by index, not seen as true in this expression
+
+@item
+@var{not_covered_false}: terms, by index, not seen as false in this expression
+@end itemize
+
 @item -H
 @itemx --human-readable
 Write counts in human readable format (like 24.6k).
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 277ac35ad16..8b783543ac9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -619,6 +619,7 @@ Objective-C and Objective-C++ Dialects}.
 @item Program Instrumentation Options
 @xref{Instrumentation Options,,Program Instrumentation Options}.
 @gccoptlist{-p  -pg  -fprofile-arcs  --coverage  -ftest-coverage @gol
+-fprofile-conditions @gol
 -fprofile-abs-path @gol
 -fprofile-dir=@var{path}  -fprofile-generate  -fprofile-generate=@var{path} @gol
 -fprofile-info-section  -fprofile-info-section=@var{name} @gol
@@ -6308,6 +6309,13 @@ poorly optimized code and is useful only in the
 case of very minor changes such as bug fixes to an existing code-base.
 Completely disabling the warning is not recommended.
 
+@item -Wno-coverage-too-many-conditions
+@opindex Wno-coverage-too-many-conditions
+@opindex Wcoverage-too-many-conditions
+Warn in case a condition have too many terms and GCC gives up coverage.
+Coverage is given up when there are more terms in the conditional than there
+are bits in a @code{gcov_type_unsigned}.  This warning is enabled by default.
+
 @item -Wno-coverage-invalid-line-number
 @opindex Wno-coverage-invalid-line-number
 @opindex Wcoverage-invalid-line-number
@@ -16163,6 +16171,13 @@ Note that if a command line directly links source files, the corresponding
 E.g. @code{gcc a.c b.c -o binary} would generate @file{binary-a.gcda} and
 @file{binary-b.gcda} files.
 
+@item -fprofile-conditions
+@opindex fprofile-conditions
+Add code so that program conditions are instrumented.  During execution the
+program records what terms in a conditional contributes to a decision.  The
+data may be used to verify that all terms in a booleans are tested and have an
+effect on the outcome of a condition.
+
 @xref{Cross-profiling}.
 
 @cindex @command{gcov}
@@ -16225,6 +16240,10 @@ executed.  When an arc is the only exit or only entrance to a block, the
 instrumentation code can be added to the block; otherwise, a new basic
 block must be created to hold the instrumentation code.
 
+With @option{-fprofile-conditions}, for each conditional in your program GCC
+creates a bitset and records the exercised boolean values that have an
+independent effect on the outcome of that expression.
+
 @need 2000
 @item -ftest-coverage
 @opindex ftest-coverage
diff --git a/gcc/gcc.cc b/gcc/gcc.cc
index 2278e2b6bb1..4016520ccd1 100644
--- a/gcc/gcc.cc
+++ b/gcc/gcc.cc
@@ -1152,7 +1152,7 @@ proper position among the other output files.  */
 	%:include(libgomp.spec)%(link_gomp)}\
     %{fgnu-tm:%:include(libitm.spec)%(link_itm)}\
     %(mflib) " STACK_SPLIT_SPEC "\
-    %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} " SANITIZER_SPEC " \
+    %{fprofile-arcs|fprofile-conditions|fprofile-generate*|coverage:-lgcov} " SANITIZER_SPEC " \
     %{!nostdlib:%{!r:%{!nodefaultlibs:%(link_ssp) %(link_gcc_c_sequence)}}}\
     %{!nostdlib:%{!r:%{!nostartfiles:%E}}} %{T*}  \n%(post_link) }}}}}}"
 #endif
@@ -1269,7 +1269,7 @@ static const char *cc1_options =
  %{!fsyntax-only:%{S:%W{o*}%{!o*:-o %w%b.s}}}\
  %{fsyntax-only:-o %j} %{-param*}\
  %{coverage:-fprofile-arcs -ftest-coverage}\
- %{fprofile-arcs|fprofile-generate*|coverage:\
+ %{fprofile-arcs|fprofile-conditions|fprofile-generate*|coverage:\
    %{!fprofile-update=single:\
      %{pthread:-fprofile-update=prefer-atomic}}}";
 
diff --git a/gcc/gcov-counter.def b/gcc/gcov-counter.def
index 6d2182bd3db..96563a59a45 100644
--- a/gcc/gcov-counter.def
+++ b/gcc/gcov-counter.def
@@ -49,3 +49,6 @@ DEF_GCOV_COUNTER(GCOV_COUNTER_IOR, "ior", _ior)
 
 /* Time profile collecting first run of a function */
 DEF_GCOV_COUNTER(GCOV_TIME_PROFILER, "time_profiler", _time_profile)
+
+/* Conditions.  The counter is interpreted as a bit-set.  */
+DEF_GCOV_COUNTER(GCOV_COUNTER_CONDS, "conditions", _ior)
diff --git a/gcc/gcov-dump.cc b/gcc/gcov-dump.cc
index 03023bfb226..6dc1df6e3e1 100644
--- a/gcc/gcov-dump.cc
+++ b/gcc/gcov-dump.cc
@@ -38,6 +38,7 @@ static void print_version (void);
 static void tag_function (const char *, unsigned, int, unsigned);
 static void tag_blocks (const char *, unsigned, int, unsigned);
 static void tag_arcs (const char *, unsigned, int, unsigned);
+static void tag_conditions (const char *, unsigned, int, unsigned);
 static void tag_lines (const char *, unsigned, int, unsigned);
 static void tag_counters (const char *, unsigned, int, unsigned);
 static void tag_summary (const char *, unsigned, int, unsigned);
@@ -77,6 +78,7 @@ static const tag_format_t tag_table[] =
   {GCOV_TAG_FUNCTION, "FUNCTION", tag_function},
   {GCOV_TAG_BLOCKS, "BLOCKS", tag_blocks},
   {GCOV_TAG_ARCS, "ARCS", tag_arcs},
+  {GCOV_TAG_CONDS, "CONDITIONS", tag_conditions},
   {GCOV_TAG_LINES, "LINES", tag_lines},
   {GCOV_TAG_OBJECT_SUMMARY, "OBJECT_SUMMARY", tag_summary},
   {0, NULL, NULL}
@@ -392,6 +394,28 @@ tag_arcs (const char *filename ATTRIBUTE_UNUSED,
     }
 }
 
+static void
+tag_conditions (const char *filename ATTRIBUTE_UNUSED,
+		unsigned tag ATTRIBUTE_UNUSED, int length ATTRIBUTE_UNUSED,
+		unsigned depth)
+{
+  unsigned n_conditions = GCOV_TAG_CONDS_NUM (length);
+
+  printf (" %u conditionals", n_conditions);
+  if (flag_dump_contents)
+    {
+      for (unsigned ix = 0; ix != n_conditions; ix++)
+	{
+	  const unsigned blockno = gcov_read_unsigned ();
+	  const unsigned nterms = gcov_read_unsigned ();
+
+	  printf ("\n");
+	  print_prefix (filename, depth, gcov_position ());
+	  printf (VALUE_PADDING_PREFIX "block %u:", blockno);
+	  printf (" %u", nterms);
+	}
+    }
+}
 static void
 tag_lines (const char *filename ATTRIBUTE_UNUSED,
 	   unsigned tag ATTRIBUTE_UNUSED, int length ATTRIBUTE_UNUSED,
diff --git a/gcc/gcov-io.h b/gcc/gcov-io.h
index e91cd736556..198c5d413eb 100644
--- a/gcc/gcov-io.h
+++ b/gcc/gcov-io.h
@@ -261,6 +261,9 @@ typedef uint64_t gcov_type_unsigned;
 #define GCOV_TAG_ARCS		 ((gcov_unsigned_t)0x01430000)
 #define GCOV_TAG_ARCS_LENGTH(NUM)  (1 + (NUM) * 2 * GCOV_WORD_SIZE)
 #define GCOV_TAG_ARCS_NUM(LENGTH)  (((LENGTH / GCOV_WORD_SIZE) - 1) / 2)
+#define GCOV_TAG_CONDS		   ((gcov_unsigned_t)0x01470000)
+#define GCOV_TAG_CONDS_LENGTH(NUM) ((NUM) * 2 * GCOV_WORD_SIZE)
+#define GCOV_TAG_CONDS_NUM(LENGTH) (((LENGTH) / GCOV_WORD_SIZE) / 2)
 #define GCOV_TAG_LINES		 ((gcov_unsigned_t)0x01450000)
 #define GCOV_TAG_COUNTER_BASE 	 ((gcov_unsigned_t)0x01a10000)
 #define GCOV_TAG_COUNTER_LENGTH(NUM) ((NUM) * 2 * GCOV_WORD_SIZE)
diff --git a/gcc/gcov.cc b/gcc/gcov.cc
index 9cf1071166f..2a144a5fcd3 100644
--- a/gcc/gcov.cc
+++ b/gcc/gcov.cc
@@ -79,6 +79,7 @@ using namespace std;
 class function_info;
 class block_info;
 class source_info;
+class condition_info;
 
 /* Describes an arc between two basic blocks.  */
 
@@ -132,6 +133,28 @@ public:
   vector<unsigned> lines;
 };
 
+class condition_info
+{
+public:
+  condition_info ();
+
+  int popcount () const;
+
+  gcov_type_unsigned truev;
+  gcov_type_unsigned falsev;
+
+  unsigned n_terms;
+};
+
+condition_info::condition_info (): truev (0), falsev (0), n_terms (0)
+{
+}
+
+int condition_info::popcount () const
+{
+    return __builtin_popcountll (truev) + __builtin_popcountll (falsev);
+}
+
 /* Describes a basic block. Contains lists of arcs to successor and
    predecessor blocks.  */
 
@@ -165,6 +188,8 @@ public:
   /* Block is a landing pad for longjmp or throw.  */
   unsigned is_nonlocal_return : 1;
 
+  condition_info conditions;
+
   vector<block_location_info> locations;
 
   struct
@@ -275,6 +300,8 @@ public:
   vector<block_info> blocks;
   unsigned blocks_executed;
 
+  vector<condition_info*> conditions;
+
   /* Raw arc coverage counts.  */
   vector<gcov_type> counts;
 
@@ -351,6 +378,9 @@ struct coverage_info
   int branches_executed;
   int branches_taken;
 
+  int conditions;
+  int conditions_covered;
+
   int calls;
   int calls_executed;
 
@@ -550,6 +580,10 @@ static int multiple_files = 0;
 
 static int flag_branches = 0;
 
+/* Output conditions (modified condition/decision coverage) */
+
+static int flag_conditions = 0;
+
 /* Show unconditional branches too.  */
 static int flag_unconditional = 0;
 
@@ -656,6 +690,7 @@ static int read_count_file (void);
 static void solve_flow_graph (function_info *);
 static void find_exception_blocks (function_info *);
 static void add_branch_counts (coverage_info *, const arc_info *);
+static void add_condition_counts (coverage_info *, const block_info *);
 static void add_line_counts (coverage_info *, function_info *);
 static void executed_summary (unsigned, unsigned);
 static void function_summary (const coverage_info *);
@@ -664,6 +699,7 @@ static const char *format_gcov (gcov_type, gcov_type, int);
 static void accumulate_line_counts (source_info *);
 static void output_gcov_file (const char *, source_info *);
 static int output_branch_count (FILE *, int, const arc_info *);
+static void output_conditions (FILE *, const block_info *);
 static void output_lines (FILE *, const source_info *);
 static string make_gcov_file_name (const char *, const char *);
 static char *mangle_name (const char *);
@@ -928,6 +964,7 @@ print_usage (int error_p)
   fnotice (file, "  -b, --branch-probabilities      Include branch probabilities in output\n");
   fnotice (file, "  -c, --branch-counts             Output counts of branches taken\n\
                                     rather than percentages\n");
+  fnotice (file, "  -g, --conditions                Include condition/decision coverage in output\n");
   fnotice (file, "  -d, --display-progress          Display progress information\n");
   fnotice (file, "  -D, --debug			    Display debugging dumps\n");
   fnotice (file, "  -f, --function-summaries        Output summaries for each function\n");
@@ -980,6 +1017,7 @@ static const struct option options[] =
   { "all-blocks",           no_argument,       NULL, 'a' },
   { "branch-probabilities", no_argument,       NULL, 'b' },
   { "branch-counts",        no_argument,       NULL, 'c' },
+  { "conditions",	    no_argument,       NULL, 'g' },
   { "json-format",	    no_argument,       NULL, 'j' },
   { "human-readable",	    no_argument,       NULL, 'H' },
   { "no-output",            no_argument,       NULL, 'n' },
@@ -1008,7 +1046,7 @@ process_args (int argc, char **argv)
 {
   int opt;
 
-  const char *opts = "abcdDfhHijklmno:pqrs:tuvwx";
+  const char *opts = "abcdDfghHijklmno:pqrs:tuvwx";
   while ((opt = getopt_long (argc, argv, opts, options, NULL)) != -1)
     {
       switch (opt)
@@ -1025,6 +1063,9 @@ process_args (int argc, char **argv)
 	case 'f':
 	  flag_function_summary = 1;
 	  break;
+	case 'g':
+	  flag_conditions = 1;
+	  break;
 	case 'h':
 	  print_usage (false);
 	  /* print_usage will exit.  */
@@ -1132,6 +1173,45 @@ output_intermediate_json_line (json::array *object,
 	  }
       }
 
+  json::array *conditions = new json::array ();
+  lineo->set ("conditions", conditions);
+  if (flag_conditions)
+  {
+    vector<block_info *>::const_iterator it;
+    for (it = line->blocks.begin (); it != line->blocks.end (); it++)
+      {
+	const condition_info& info = (*it)->conditions;
+	if (info.n_terms == 0)
+	    continue;
+
+	const int count = 2 * info.n_terms;
+	const int covered = info.popcount ();
+
+	json::object *cond = new json::object ();
+	cond->set ("count", new json::integer_number (count));
+	cond->set ("covered", new json::integer_number (covered));
+
+	json::array *mtrue = new json::array ();
+	json::array *mfalse = new json::array ();
+	cond->set ("not_covered_true", mtrue);
+	cond->set ("not_covered_false", mfalse);
+
+	if (count != covered)
+	  {
+	    for (unsigned i = 0; i < info.n_terms; i++)
+	      {
+		gcov_type_unsigned index = 1;
+		index <<= i;
+		if (!(index & info.truev))
+		    mtrue->append (new json::integer_number (i));
+		if (!(index & info.falsev))
+		    mfalse->append (new json::integer_number (i));
+	      }
+	  }
+	conditions->append (cond);
+      }
+  }
+
   object->append (lineo);
 }
 
@@ -1956,6 +2036,28 @@ read_graph_file (void)
 		  }
 	    }
 	}
+      else if (fn && tag == GCOV_TAG_CONDS)
+	{
+	  unsigned num_dests = GCOV_TAG_CONDS_NUM (length);
+
+	  if (!fn->conditions.empty ())
+	    fnotice (stderr, "%s:already seen conditions for '%s'\n",
+		     bbg_file_name, fn->get_name ());
+	  else
+	    fn->conditions.resize (num_dests);
+
+	  for (unsigned i = 0; i < num_dests; ++i)
+	    {
+	      unsigned idx = gcov_read_unsigned ();
+
+	      if (idx >= fn->blocks.size ())
+		goto corrupt;
+
+	      condition_info *info = &fn->blocks[idx].conditions;
+	      info->n_terms = gcov_read_unsigned ();
+	      fn->conditions[i] = info;
+	    }
+	}
       else if (fn && tag == GCOV_TAG_LINES)
 	{
 	  unsigned blockno = gcov_read_unsigned ();
@@ -2086,11 +2188,26 @@ read_count_file (void)
 	      goto cleanup;
 	    }
 	}
-      else if (tag == GCOV_TAG_FOR_COUNTER (GCOV_COUNTER_ARCS) && fn)
+      else if (tag == GCOV_TAG_FOR_COUNTER (GCOV_COUNTER_CONDS) && fn)
 	{
+	  length = abs (read_length);
+	  if (length != GCOV_TAG_COUNTER_LENGTH (2 * fn->conditions.size ()))
+	      goto mismatch;
+
+	  if (read_length > 0)
+	    {
+	      for (ix = 0; ix != fn->conditions.size (); ix++)
+		{
+		  fn->conditions[ix]->truev  |= gcov_read_counter ();
+		  fn->conditions[ix]->falsev |= gcov_read_counter ();
+		}
+	    }
+	}
+      else if (tag == GCOV_TAG_FOR_COUNTER (GCOV_COUNTER_ARCS) && fn)
+      {
 	  length = abs (read_length);
 	  if (length != GCOV_TAG_COUNTER_LENGTH (fn->counts.size ()))
-	    goto mismatch;
+	      goto mismatch;
 
 	  if (read_length > 0)
 	    for (ix = 0; ix != fn->counts.size (); ix++)
@@ -2430,6 +2547,13 @@ add_branch_counts (coverage_info *coverage, const arc_info *arc)
     }
 }
 
+static void
+add_condition_counts (coverage_info *coverage, const block_info *block)
+{
+  coverage->conditions += 2 * block->conditions.n_terms;
+  coverage->conditions_covered += block->conditions.popcount ();
+}
+
 /* Format COUNT, if flag_human_readable_numbers is set, return it human
    readable format.  */
 
@@ -2533,6 +2657,18 @@ file_summary (const coverage_info *coverage)
 		 coverage->calls);
       else
 	fnotice (stdout, "No calls\n");
+
+    }
+
+  if (flag_conditions)
+    {
+      if (coverage->conditions)
+	fnotice (stdout, "Condition outcomes covered:%s of %d\n",
+		 format_gcov (coverage->conditions_covered,
+			      coverage->conditions, 2),
+		 coverage->conditions);
+      else
+	fnotice (stdout, "No conditions\n");
     }
 }
 
@@ -2767,6 +2903,12 @@ static void accumulate_line_info (line_info *line, source_info *src,
 	 it != line->branches.end (); it++)
       add_branch_counts (&src->coverage, *it);
 
+  if (add_coverage)
+    for (vector<block_info *>::iterator it = line->blocks.begin ();
+	 it != line->blocks.end (); it++)
+      add_condition_counts (&src->coverage, *it);
+
+
   if (!line->blocks.empty ())
     {
       /* The user expects the line count to be the number of times
@@ -2868,6 +3010,33 @@ accumulate_line_counts (source_info *src)
       }
 }
 
+static void
+output_conditions (FILE *gcov_file, const block_info *binfo)
+{
+    const condition_info& info = binfo->conditions;
+    if (info.n_terms == 0)
+	return;
+
+    const int expected = 2 * info.n_terms;
+    const int got = info.popcount ();
+
+    fnotice (gcov_file, "condition outcomes covered %d/%d\n", got, expected);
+    if (expected == got)
+	return;
+
+    for (unsigned i = 0; i < info.n_terms; i++)
+    {
+	gcov_type_unsigned index = 1;
+	index <<= i;
+	if ((index & info.truev & info.falsev))
+	    continue;
+
+	const char *t = (index & info.truev) ? "" : "true";
+	const char *f = (index & info.falsev) ? "" : " false";
+	fnotice (gcov_file, "condition %2u not covered (%s%s)\n", i, t, f + !t[0]);
+    }
+}
+
 /* Output information about ARC number IX.  Returns nonzero if
    anything is output.  */
 
@@ -3078,16 +3247,29 @@ output_line_details (FILE *f, const line_info *line, unsigned line_num)
 	  if (flag_branches)
 	    for (arc = (*it)->succ; arc; arc = arc->succ_next)
 	      jx += output_branch_count (f, jx, arc);
+
+	  if (flag_conditions)
+	      output_conditions (f, *it);
 	}
     }
-  else if (flag_branches)
+  else
     {
-      int ix;
+      if (flag_branches)
+	{
+	  int ix;
+
+	  ix = 0;
+	  for (vector<arc_info *>::const_iterator it = line->branches.begin ();
+		  it != line->branches.end (); it++)
+	      ix += output_branch_count (f, ix, (*it));
+	}
 
-      ix = 0;
-      for (vector<arc_info *>::const_iterator it = line->branches.begin ();
-	   it != line->branches.end (); it++)
-	ix += output_branch_count (f, ix, (*it));
+      if (flag_conditions)
+	{
+	  for (vector<block_info *>::const_iterator it = line->blocks.begin ();
+	       it != line->blocks.end (); it++)
+	      output_conditions (f, *it);
+	}
     }
 }
 
diff --git a/gcc/ipa-inline.cc b/gcc/ipa-inline.cc
index 14969198cde..3e37305843e 100644
--- a/gcc/ipa-inline.cc
+++ b/gcc/ipa-inline.cc
@@ -646,7 +646,7 @@ can_early_inline_edge_p (struct cgraph_edge *e)
 			 "  edge not inlinable: not in SSA form\n");
       return false;
     }
-  else if (profile_arc_flag
+  else if ((profile_arc_flag || profile_condition_flag)
 	   && ((lookup_attribute ("no_profile_instrument_function",
 				 DECL_ATTRIBUTES (caller->decl)) == NULL_TREE)
 	       != (lookup_attribute ("no_profile_instrument_function",
diff --git a/gcc/ipa-split.cc b/gcc/ipa-split.cc
index 16734617d03..07d2b17ab12 100644
--- a/gcc/ipa-split.cc
+++ b/gcc/ipa-split.cc
@@ -1929,7 +1929,8 @@ pass_split_functions::gate (function *)
   /* When doing profile feedback, we want to execute the pass after profiling
      is read.  So disable one in early optimization.  */
   return (flag_partial_inlining
-	  && !profile_arc_flag && !flag_branch_probabilities);
+      && !profile_arc_flag && !flag_branch_probabilities
+      && !profile_condition_flag);
 }
 
 } // anon namespace
diff --git a/gcc/passes.cc b/gcc/passes.cc
index 347214e81d0..907ac90aa61 100644
--- a/gcc/passes.cc
+++ b/gcc/passes.cc
@@ -352,7 +352,8 @@ finish_optimization_passes (void)
   gcc::dump_manager *dumps = m_ctxt->get_dumps ();
 
   timevar_push (TV_DUMP);
-  if (profile_arc_flag || flag_test_coverage || flag_branch_probabilities)
+  if (profile_arc_flag || profile_condition_flag || flag_test_coverage
+      || flag_branch_probabilities)
     {
       dumps->dump_start (pass_profile_1->static_pass_number, NULL);
       end_branch_prob ();
diff --git a/gcc/profile.cc b/gcc/profile.cc
index 1527a04124f..1c9a426baa8 100644
--- a/gcc/profile.cc
+++ b/gcc/profile.cc
@@ -66,9 +66,19 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfgloop.h"
 #include "sreal.h"
 #include "file-prefix-map.h"
+#include "stringpool.h"
 
 #include "profile.h"
 
+struct condcov;
+struct condcov *find_conditions (struct function*);
+unsigned cov_length (const struct condcov*);
+array_slice<basic_block> cov_blocks (struct condcov*, unsigned);
+array_slice<gcov_type_unsigned > cov_masks (struct condcov*, unsigned);
+void cov_free (struct condcov*);
+int instrument_decisions (array_slice<basic_block>, unsigned, tree*,
+			  gcov_type_unsigned*);
+
 /* Map from BBs/edges to gcov counters.  */
 vec<gcov_type> bb_gcov_counts;
 hash_map<edge,gcov_type> *edge_gcov_counts;
@@ -100,6 +110,7 @@ static int total_num_passes;
 static int total_num_times_called;
 static int total_hist_br_prob[20];
 static int total_num_branches;
+static int total_num_conds;
 
 /* Forward declarations.  */
 static void find_spanning_tree (struct edge_list *);
@@ -1155,6 +1166,12 @@ read_thunk_profile (struct cgraph_node *node)
    the flow graph that are needed to reconstruct the dynamic behavior of the
    flow graph.  This data is written to the gcno file for gcov.
 
+   When FLAG_PROFILE_CONDITIONS is nonzero, this functions instruments the
+   edges in the control flow graph to track what conditions are evaluated to in
+   order to determine what conditions are covered and have an independent
+   effect on the outcome (modified condition/decision coverage).  This data is
+   written to the gcno file for gcov.
+
    When FLAG_BRANCH_PROBABILITIES is nonzero, this function reads auxiliary
    information from the gcda file containing edge count information from
    previous executions of the function being compiled.  In this case, the
@@ -1173,6 +1190,7 @@ branch_prob (bool thunk)
   struct edge_list *el;
   histogram_values values = histogram_values ();
   unsigned cfg_checksum, lineno_checksum;
+  bool output_to_file;
 
   total_num_times_called++;
 
@@ -1397,10 +1415,18 @@ branch_prob (bool thunk)
 
   /* Write the data from which gcov can reconstruct the basic block
      graph and function line numbers (the gcno file).  */
+  output_to_file = false;
   if (coverage_begin_function (lineno_checksum, cfg_checksum))
     {
       gcov_position_t offset;
 
+      /* The condition coverage needs a deeper analysis to identify expressions
+       * of conditions, which means it is not yet ready to write to the gcno
+       * file.  It will write its entries later, but needs to know if it do it
+       * in the first place, which is controlled by the return value of
+       * coverage_begin_function.  */
+      output_to_file = true;
+
       /* Basic block flags */
       offset = gcov_write_tag (GCOV_TAG_BLOCKS);
       gcov_write_unsigned (n_basic_blocks_for_fn (cfun));
@@ -1514,29 +1540,74 @@ branch_prob (bool thunk)
 
   remove_fake_edges ();
 
+  if (profile_condition_flag || profile_arc_flag)
+      gimple_init_gcov_profiler ();
+
+  if (profile_condition_flag)
+    {
+      struct condcov *cov = find_conditions (cfun);
+      gcc_assert (cov);
+      const unsigned nconds = cov_length (cov);
+      total_num_conds += nconds;
+
+      if (coverage_counter_alloc (GCOV_COUNTER_CONDS, 2 * nconds))
+	{
+	  /* Add two extra variables to the function for the local
+	     accumulators, which are zero'd on the entry of a new conditional.
+	     The local accumulators are shared between decisions in order to
+	     use less stack space.  */
+	  tree accu[2] = {
+	    build_decl (UNKNOWN_LOCATION, VAR_DECL,
+			get_identifier ("__accu_t"), get_gcov_type ()),
+	    build_decl (UNKNOWN_LOCATION, VAR_DECL,
+			get_identifier ("__accu_f"), get_gcov_type ()),
+	  };
+
+	  gcov_position_t offset {};
+	  if (output_to_file)
+	      offset = gcov_write_tag (GCOV_TAG_CONDS);
+
+	  for (unsigned i = 0; i < nconds; ++i)
+	    {
+	      array_slice<basic_block> expr = cov_blocks (cov, i);
+	      array_slice<gcov_type_unsigned> masks = cov_masks (cov, i);
+	      gcc_assert (expr.is_valid ());
+	      gcc_assert (masks.is_valid ());
+
+	      int terms = instrument_decisions (expr, i, accu, masks.begin ());
+	      if (output_to_file)
+		{
+		  gcov_write_unsigned (expr.front ()->index);
+		  gcov_write_unsigned (terms);
+		}
+	    }
+	  if (output_to_file)
+	      gcov_write_length (offset);
+	}
+      cov_free (cov);
+    }
+
   /* For each edge not on the spanning tree, add counting code.  */
   if (profile_arc_flag
       && coverage_counter_alloc (GCOV_COUNTER_ARCS, num_instrumented))
     {
       unsigned n_instrumented;
 
-      gimple_init_gcov_profiler ();
-
       n_instrumented = instrument_edges (el);
 
       gcc_assert (n_instrumented == num_instrumented);
 
       if (flag_profile_values)
 	instrument_values (values);
-
-      /* Commit changes done by instrumentation.  */
-      gsi_commit_edge_inserts ();
     }
 
   free_aux_for_edges ();
 
   values.release ();
   free_edge_list (el);
+  /* Commit changes done by instrumentation.  */
+  gsi_commit_edge_inserts ();
+
   coverage_end_function (lineno_checksum, cfg_checksum);
   if (flag_branch_probabilities
       && (profile_status_for_fn (cfun) == PROFILE_READ))
@@ -1666,6 +1737,7 @@ init_branch_prob (void)
   total_num_passes = 0;
   total_num_times_called = 0;
   total_num_branches = 0;
+  total_num_conds = 0;
   for (i = 0; i < 20; i++)
     total_hist_br_prob[i] = 0;
 }
@@ -1705,5 +1777,7 @@ end_branch_prob (void)
 		     (total_hist_br_prob[i] + total_hist_br_prob[19-i]) * 100
 		     / total_num_branches, 5*i, 5*i+5);
 	}
+      fprintf (dump_file, "Total number of conditions: %d\n",
+	       total_num_conds);
     }
 }
diff --git a/gcc/testsuite/g++.dg/gcov/gcov-18.C b/gcc/testsuite/g++.dg/gcov/gcov-18.C
new file mode 100644
index 00000000000..310ed5297c0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/gcov/gcov-18.C
@@ -0,0 +1,234 @@
+/* { dg-options "--coverage -fprofile-conditions -std=c++11" } */
+/* { dg-do run { target native } } */
+
+#include <vector>
+#include <stdexcept>
+
+class nontrivial_destructor
+{
+public:
+    explicit nontrivial_destructor (int v) : val (v) {}
+    ~nontrivial_destructor () {}
+
+    explicit operator bool() const { return bool(val); }
+
+    int val;
+};
+
+int identity (int x) { return x; }
+int throws (int) { throw std::runtime_error("exception"); }
+
+int throw_if (int x)
+{
+    if (x) /* conditions(1/2) true(0) */
+	   /* conditions(end) */
+	throw std::runtime_error("exception");
+    return x;
+}
+
+/* used for side effects to insert nodes in conditional bodies etc. */
+int x = 0;
+
+/* conditionals work in the presence of non-trivial destructors */
+void mcdc001a (int a)
+{
+    nontrivial_destructor v (a);
+
+    if (v.val > 0) /* conditions(2/2) */
+	x = v.val;
+    else
+	x = -v.val;
+}
+
+/* non-trivial destructor in-loop temporary */
+nontrivial_destructor
+mcdc002a (int a, int b)
+{
+    for (int i = 0; i < a; i++) /* conditions(2/2) */
+    {
+	nontrivial_destructor tmp (a);
+	if (tmp.val % b) /* conditions(2/2) */
+	    return nontrivial_destructor (0);
+	x += i;
+    } /* conditions(suppress) */
+      /* conditions(end) */
+
+    return nontrivial_destructor (a * b);
+}
+
+/* conditional in constructor */
+void mcdc003a (int a)
+{
+    class C
+    {
+    public:
+	explicit C (int e) : v (e)
+	{
+	    if (e) /* conditions(1/2) false(0) */
+		v = x - e;
+	}
+	int v;
+    };
+
+    C c (a);
+    if (c.v > 2) /* conditions(1/2) true(0) */
+		 /* conditions(end) */
+	x = c.v + a;
+}
+
+/* conditional in destructor */
+void mcdc004a (int a)
+{
+    class C
+    {
+    public:
+	explicit C (int e) : v (e) {}
+	~C ()
+	{
+	    if (v) /* conditions(2/2) */
+		x = 2 * v;
+	}
+	int v;
+    };
+
+    C c (a);
+    x = 1; // arbitrary action between ctor+dtor
+}
+
+/* conditional in try */
+void mcdc005a (int a)
+{
+    try
+    {
+	if (a) /* conditions(1/2) true(0) */
+	       /* conditions(end) */
+	    x = 2 * identity (a);
+	else
+	    x = 1;
+    }
+    catch (...)
+    {
+	x = 0;
+    }
+}
+
+/* conditional in catch */
+void mcdc006a (int a) {
+    try
+    {
+	throws (a);
+    }
+    catch (std::exception&)
+    {
+	if (a) /* conditions(1/2) false(0) */
+	       /* conditions(end) */
+	    x = identity (a);
+	else
+	    x = 0;
+    }
+}
+
+void mcdc006b (int a)
+{
+    if (a) /* conditions(1/2) true(0) */
+	   /* conditions(end) */
+	throws (a);
+    else
+	x = 1;
+}
+
+void mcdc006c (int a) try
+{
+    throws (a);
+}
+catch (...) {
+    if (a) /* conditions(2/2) */
+	x = 5;
+}
+
+/* temporary with destructor as term */
+void mcdc007a (int a, int b)
+{
+    x = a && nontrivial_destructor (b); /* conditions(3/4) false(1) destructor() */
+}
+
+void mcdc007b (int a, int b)
+{
+    if (a || throw_if (b)) /* conditions(3/4) true(1) destructor() */
+	x = -1;
+    else
+	x = 1;
+}
+
+void mcdc007c (int a, int b)
+{
+    if (throw_if (a) || throw_if (b)) /* conditions(2/4) true(0 1) destructor() */
+	x = -1;
+    else
+	x = 1;
+}
+
+/* destructor with delete */
+void mcdc008a (int a)
+{
+    class C
+    {
+    public:
+        int size = 5;
+        int* ptr = nullptr;
+
+        explicit C (int v) : size (v + 5), ptr (new int[size]) /* conditions(suppress) */
+							       /* conditions(end) */
+        {
+	    for (int i = 0; i < size; i++) /* conditions(2/2) */
+		ptr[i] = i + 1;
+        }
+        ~C()
+        {
+	    // delete with implicit nullptr check
+	    delete ptr; /* conditions(1/2) false(0) */
+			/* conditions(end) */
+	}
+    };
+
+    C c (a);
+    if (c.ptr[a + 1]) /* conditions(1/2) false(0) */
+	x = a;
+}
+
+int
+main (void)
+{
+    mcdc001a (0);
+    mcdc001a (1);
+
+    mcdc002a (1, 1);
+    mcdc002a (1, 2);
+
+    mcdc003a (1);
+
+    mcdc004a (0);
+    mcdc004a (1);
+
+    mcdc005a (0);
+
+    mcdc006a (1);
+
+    mcdc006b (0);
+
+    mcdc006c (0);
+    mcdc006c (1);
+
+    mcdc007a (0, 0);
+    mcdc007a (1, 1);
+
+    mcdc007b (0, 0);
+    mcdc007b (1, 0);
+
+    mcdc007c (0, 0);
+
+    mcdc008a (1);
+
+}
+
+/* { dg-final { run-gcov conditions { --conditions gcov-18.C } } } */
diff --git a/gcc/testsuite/gcc.misc-tests/gcov-19.c b/gcc/testsuite/gcc.misc-tests/gcov-19.c
new file mode 100644
index 00000000000..1adff7c76f4
--- /dev/null
+++ b/gcc/testsuite/gcc.misc-tests/gcov-19.c
@@ -0,0 +1,1250 @@
+/* { dg-options "-fprofile-conditions -ftest-coverage" } */
+/* { dg-do run { target native } } */
+
+/* some side effect to stop branches from being pruned */
+int x = 0;
+
+/* || works */
+void
+mcdc001a (int a, int b)
+{
+    if (a || b) /* conditions(1/4) true(0) false(0 1) */
+		/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc001b (int a, int b)
+{
+    if (a || b) /* conditions(3/4) true(0) */
+		/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc001c (int a, int b)
+{
+    if (a || b) /* conditions(4/4) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc001d (int a, int b, int c)
+{
+    if (a || b || c) /* conditions(2/6) false(0 1 2) true(2) */
+		     /* conditions(end) */
+	x = 1;
+}
+
+/* && works */
+void
+mcdc002a (int a, int b)
+{
+    if (a && b) /* conditions(1/4) true(0 1) false(0) */
+		/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc002b (int a, int b)
+{
+    if (a && b) /* conditions(3/4) false(0) */
+		/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc002c (int a, int b)
+{
+    if (a && b) /* conditions(4/4) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc002d (int a, int b, int c)
+{
+    if (a && b && c) /* conditions(4/6) false(0 2) */
+		     /* conditions(end) */
+	x = 1;
+}
+
+/* negation works */
+void
+mcdc003a (int a, int b)
+{
+    if (!a || !b) /* conditions(2/4) false(0 1) */
+		  /* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+/* single conditionals with and without else */
+void
+mcdc004a (int a)
+{
+    if (a) /* conditions(1/2) true(0) */
+	   /* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc004b (int a)
+{
+    if (a) /* conditions(2/2) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc004c (int a)
+{
+    if (a) /* conditions(1/2) false(0) */
+	   /* conditions(end) */
+	x = 1;
+}
+
+void
+mcdc004d (int a, int b, int c)
+{
+    /* With no else this is interpreted as (a && (b || c)) */
+    if (a)  /* conditions(3/6) true(2) false(1 2)*/
+    {
+	if (b || c)
+	    x = a + b + c;
+    }
+}
+
+void
+mcdc004e (int a, int b, int c)
+{
+    /* With the else, this is interpreted as 2 expressions */
+    if (a)  /* conditions(2/2) */
+    {
+	if (b || c) /* conditions(1/4) true(1) false(0 1) */
+	    x = a + b + c;
+    }
+    else
+    {
+	x = c;
+    }
+}
+
+/* mixing && and || works */
+void
+mcdc005a (int a, int b, int c)
+{
+    if ((a && b) || c) /* conditions(1/6) true(0 1) false(0 1 2) */
+		       /* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc005b (int a, int b, int c, int d)
+{
+    /* This is where masking MC/DC gets unintuitive:
+
+       1 1 0 0 => covers 1 (d = 0) as && 0 masks everything to the left
+       1 0 0 0 => covers 2 (b = 0, c = 0) as (a && 0) masks a and d is never
+       evaluated. */
+    if ((a && (b || c)) && d) /* conditions(3/8) true(0 1 2 3) false(0) */
+			      /* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc005c (int a, int b, int c, int d)
+{
+    if (a || (b && c) || d) /* conditions(2/8) true(0 3) false(0 1 2 3) */
+			    /* conditions(end) */
+        x = a + b + c + d;
+}
+
+void
+mcdc005d (int a, int b, int c, int d)
+{
+    /* This test is quite significant - it has a single input
+       (1, 0, 0, 0) and tests specifically for when a multi-term left operand
+       is masked. d = 0 should mask a || b and for the input there are no other
+       sources for masking a (since b = 0). */
+    if ((a || b) && (c || d)) /* conditions(2/8) true(0 1 2 3) false(0 1) */
+			      /* conditions(end) */
+	x = a + b;
+    else
+	x = c + d;
+}
+
+/* nested conditionals */
+void
+mcdc006a (int a, int b, int c, int d, int e)
+{
+    if (a) /* conditions(2/2) */
+    {
+	if (b && c) /* conditions(3/4) false(1) */
+		    /* conditions(end) */
+	    x = 1;
+	else
+	    x = 2;
+    }
+    else
+    {
+	if (c || d) /* conditions(2/4) true(0 1) */
+		    /* conditions(end) */
+	    x = 3;
+	else
+	    x = 4;
+    }
+}
+
+void
+mcdc006b (int a, int b, int c)
+{
+    if (a) /* conditions(6/6) */
+	if (b)
+	    if (c)
+		x = a + b + c;
+}
+
+void
+mcdc006c (int a, int b, int c)
+{
+    if (a) /* conditions(2/2) */
+    {
+	if (b) /*conditions(2/2) */
+	{
+	    if (c) /* conditions(2/2) */
+	    {
+		x = a + b + c;
+	    }
+	}
+	else
+	{
+	    x = b;
+	}
+    }
+    else
+    {
+	x = a;
+    }
+}
+
+/* else/if */
+void
+mcdc007a (int a, int b, int c, int d)
+{
+    if (a) /* conditions(2/2) */
+    {
+	if (b) /* conditions(1/2) true(0) */
+	       /* conditions(end) */
+	    x = 1;
+	else
+	    x = 2;
+    }
+    else if (c) /* conditions(2/2) */
+    {
+	if (d) /* conditions(1/2) true(0) */
+	       /* conditions(end) */
+	    x = 3;
+	else
+	    x = 4;
+    }
+}
+
+void
+mcdc007b (int a, int b, int c)
+{
+    goto begin;
+then:
+    x = 1;
+    return;
+begin:
+    /* Evaluates to if (a || b || c) x = 1 */
+    if (a)	    /* conditions(5/6) true(2) */
+		    /* conditions(end) */
+	goto then;
+    else if (b)
+	goto then;
+    else if (c)
+	goto then;
+}
+
+void
+mcdc007c (int a, int b, int c)
+{
+    goto begin;
+then1:
+    x = 1;
+    return;
+then2:
+    x = 1;
+    return;
+then3:
+    x = 1;
+    return;
+begin:
+    /* similar to if (a || b || c) x = 1 */
+    if (a) /* conditions(2/2) */
+	goto then1;
+    else if (b) /* conditions(2/2) */
+	goto then2;
+    else if (c) /* conditions(1/2) true(0) */
+		/* conditions(end) */
+	goto then3;
+}
+
+/* while loop */
+void
+mcdc008a (int a)
+{
+    while (a < 10) /* conditions(2/2) */
+	x = a++;
+}
+
+void
+mcdc008b (int a)
+{
+    while (a > 10) /* conditions(1/2) true(0) */
+		   /* conditions(end) */
+	x = a--;
+}
+
+void
+mcdc008c (int a)
+{
+    // should work, even with no body
+    while (a) /* conditions(2/2) */
+	break;
+}
+
+void
+mcdc008d (int a, int b, int c, int d)
+{
+    /* multi-term loop conditional */
+    while ((a && (b || c)) && d) /* conditions(8/8) */
+	a = b = c = d = 0;
+}
+
+void
+mcdc009a (int a, int b)
+{
+    while (a > 0 && b > 0) /* conditions(3/4) false(1) */
+			   /* conditions(end) */
+	x = a--;
+}
+
+/* for loop */
+void
+mcdc010a(int a, int b)
+{
+    for (int i = 0; i < b; i++) /* conditions(2/2) */
+    {
+	if (a < b) /* conditions(2/2) */
+	    x = 1;
+	else
+	    x = a += 2;
+    }
+}
+
+void
+mcdc010b ()
+{
+    for (int a = 0; a <= 1; ++a) /* conditions(2/2) */
+    {
+	x = a;
+    }
+}
+
+int always (int x) { (void) x; return 1; }
+
+/* no-condition infinite loops */
+void
+mcdc010c (int a)
+{
+    for (;;)
+    {
+	if (always(a)) /* conditions(1/2) false(0) */
+		       /* conditions(end) */
+	{
+	    x = a;
+	    break;
+	}
+	x += a + 1;
+    }
+}
+
+/* conditionals without control flow constructs work */
+void
+mcdc011a (int a, int b, int c)
+{
+    x = (a && b) || c; /* conditions(5/6) false(1) */
+		       /* conditions(end) */
+}
+
+/* sequential expressions are handled independently */
+void
+mcdc012a (int a, int b, int c)
+{
+    if (a || b) /* conditions(3/4) true(0) */
+		/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+
+    if (c) /* conditions(2/2) */
+	x = 1;
+}
+
+/*
+ * cannot ever satisfy MC/DC, even with all input combinations, because not all
+ * variables independently affect the decision
+ */
+void
+mcdc013a (int a, int b, int c)
+{
+    (void)b;
+    /*
+     * Specification: (a && b) || c
+     *
+     * But the expression was implemented wrong. This has branch coverage, but
+     * not MC/DC
+     */
+    if ((a && !c) || c) /* conditions(5/6) false(1) */
+	/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+void
+mcdc014a ()
+{
+    int conds[64] = { 0 };
+    /* conditions(64/128) true(0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63) */
+    x = conds[ 0] || conds[ 1] || conds[ 2] || conds[ 3] || conds[ 4] ||
+	conds[ 5] || conds[ 6] || conds[ 7] || conds[ 8] || conds[ 9] ||
+	conds[10] || conds[11] || conds[12] || conds[13] || conds[14] ||
+	conds[15] || conds[16] || conds[17] || conds[18] || conds[19] ||
+	conds[20] || conds[21] || conds[22] || conds[23] || conds[24] ||
+	conds[25] || conds[26] || conds[27] || conds[28] || conds[29] ||
+	conds[30] || conds[31] || conds[32] || conds[33] || conds[34] ||
+	conds[35] || conds[36] || conds[37] || conds[38] || conds[39] ||
+	conds[40] || conds[41] || conds[42] || conds[43] || conds[44] ||
+	conds[45] || conds[46] || conds[47] || conds[48] || conds[49] ||
+	conds[50] || conds[51] || conds[52] || conds[53] || conds[54] ||
+	conds[55] || conds[56] || conds[57] || conds[58] || conds[59] ||
+	conds[60] || conds[61] || conds[62] || conds[63]
+	;  /* conditions(end) */
+}
+
+/* early returns */
+void
+mcdc015a (int a, int b)
+{
+    if (a) /* conditions(2/2) */
+	return;
+
+    if (b) /* conditions(1/2) true(0) */
+	   /* conditions(end) */
+	x = 1;
+}
+
+void
+mcdc015b (int a, int b)
+{
+    for (int i = 5; i > a; i--) /* conditions(2/2) */
+    {
+	if (i == b) /* conditions(2/2) */
+	    return;
+	x = i;
+    }
+}
+
+void
+mcdc015c (int a, int b)
+{
+    for (int i = 5; i > a; i--) /* conditions(2/2) */
+    {
+	if (i == b) /* conditions(2/2) */
+	{
+	    x = 0;
+	    return;
+	}
+	else
+	{
+	    x = 1;
+	    return;
+	}
+
+	x = i;
+    }
+}
+
+
+/* check nested loops */
+void
+mcdc016a (int a, int b)
+{
+    for (int i = 0; i < a; i++) /* conditions(2/2) */
+	for (int k = 0; k < b; k++) /* conditions(2/2) */
+	    x = i + k;
+}
+
+void
+mcdc016b (int a, int b)
+{
+    for (int i = 0; i < a; i++) /* conditions(2/2) */
+    {
+	if (a > 5) /* conditions(2/2) */
+	    break;
+
+	for (int k = 0; k < b; k++) /* conditions(2/2) */
+	    x = i + k;
+    }
+}
+
+void
+mcdc016c (int a, int b)
+{
+    for (int i = 0; i < a; i++) /* conditions(2/2) */
+    {
+	if (a > 5) /* conditions(1/2) true(0) */
+		   /* conditions(end) */
+	    return;
+
+	for (int k = 0; k < b; k++) /* conditions(2/2) */
+	    x = i + k;
+    }
+}
+
+void
+mcdc016d (int a, int b)
+{
+    for (int i = 0; i < a; i++) /* conditions(2/2) */
+    {
+	for (int k = 0; k < 5; k++) /* conditions(2/2) */
+	{
+	    if (b > 5) /* conditions(1/2) true(0) */
+		       /* conditions(end) */
+		return;
+	    x = i + k;
+	}
+
+    }
+}
+
+/* do-while loops */
+void
+mcdc017a (int a)
+{
+    do
+    {
+	a--;
+    } while (a > 0); /* conditions(2/2) */
+}
+
+void
+noop () {}
+
+void
+mcdc017b (int a, int b)
+{
+    do
+    {
+	/*
+	 * This call is important; it can add more nodes to the body in the
+	 * CFG, which has changes how close exits and breaks are to the loop
+	 * conditional.
+	 */
+	noop ();
+	a--;
+	if (b) /* conditions(2/2) */
+	    break;
+
+    } while (a > 0); /* conditions(2/2) */
+}
+
+void
+mcdc017c (int a, int b)
+{
+    int left = 0;
+    int right = 0;
+    int n = a + b;
+    do
+    {
+	if (a) /* conditions(1/2) false(0) */
+	       /* conditions(end) */
+	{
+	    left = a > left ? b : left; /* conditions(2/2) */
+	}
+	if (b) /* conditions(1/2) false(0) */
+	{
+	    right = b > right ? a : right; /* conditions(2/2) */
+	}
+    } while (n-- > 0); /* conditions(2/2) */
+}
+
+int id  (int x) { return  x; }
+int inv (int x) { return !x; }
+
+/* collection of odd cases lifted-and-adapted from real-world code */
+int mcdc018a (int a, int b, int c, int d, int e, int f, int g, int len)
+{
+    int n;
+    /* adapted from zlib/gz_read */
+    do
+    {
+	n = -1;
+	if (n > len) /* conditions(2/2) */
+	    n = len;
+
+	if (b) /* conditions(2/2) */
+	{
+	    if (b < 5) /* conditions(2/2) */
+		x = 1;
+	    noop();
+	}
+	else if (c && d) /* conditions(3/4) false(1) */
+	{
+	    x = 2;
+	    break;
+	}
+	else if (e || f) /* conditions(2/4) false(0 1) */
+			 /* conditions(end) */
+	{
+	    if (id(g)) /* conditions(2/2) */
+		return 0;
+	    continue;
+	}
+    } while (a-- > 0); /* conditions(2/2) */
+
+    return 1;
+}
+
+void
+mcdc018b (int a, int b, int c)
+{
+    int n;
+    while (a) /* conditions(2/2) */
+    {
+	/* else block does not make a difference for the problem, but ensures
+	   loop termination. */
+	if (b) /* conditions(2/2) */
+	    n = c ? 0 : 0; // does not show up in CFG (embedded in the block)
+	else
+	    n = 0;
+	a = n;
+    }
+}
+
+/* Adapted from zlib/compress2 */
+void
+mcdc018c (int a, int b)
+{
+    int err;
+    do
+    {
+	a = inv (a);
+	err = a;
+    } while (err); /* conditions(1/2) true(0) */
+		   /* conditions(end) */
+
+    a = id (a);
+    if (a) /* conditions(1/2) true(0) */
+	x *= a + 1;
+}
+
+/* too many conditions, coverage gives up */
+void
+mcdc019a ()
+{
+    int conds[65] = { 0 };
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wcoverage-too-many-conditions"
+    x = conds[ 0] || conds[ 1] || conds[ 2] || conds[ 3] || conds[ 4] ||
+	conds[ 5] || conds[ 6] || conds[ 7] || conds[ 8] || conds[ 9] ||
+	conds[10] || conds[11] || conds[12] || conds[13] || conds[14] ||
+	conds[15] || conds[16] || conds[17] || conds[18] || conds[19] ||
+	conds[20] || conds[21] || conds[22] || conds[23] || conds[24] ||
+	conds[25] || conds[26] || conds[27] || conds[28] || conds[29] ||
+	conds[30] || conds[31] || conds[32] || conds[33] || conds[34] ||
+	conds[35] || conds[36] || conds[37] || conds[38] || conds[39] ||
+	conds[40] || conds[41] || conds[42] || conds[43] || conds[44] ||
+	conds[45] || conds[46] || conds[47] || conds[48] || conds[49] ||
+	conds[50] || conds[51] || conds[52] || conds[53] || conds[54] ||
+	conds[55] || conds[56] || conds[57] || conds[58] || conds[59] ||
+	conds[60] || conds[61] || conds[62] || conds[63] || conds[64]
+	;
+    #pragma GCC diagnostic pop
+}
+
+/* ternary */
+void
+mcdc020a (int a)
+{
+    // special case, this can be reduced to:
+    // _1 = argc != 0;
+    // e = (int) _1;
+    x = a ? 1 : 0;
+
+    // changing to different int makes branch
+    x = a ? 2 : 1; /* conditions(2/2) */
+}
+
+void
+mcdc020b (int a, int b)
+{
+    x = (a || b) ? 1 : 0; /* conditions(3/4) true(1) */
+}
+
+void
+mcdc020c (int a, int b)
+{
+    x = a ? 0
+	: b ? 1 /* conditions(2/2) */
+	: 2;    /* conditions(1/2) false(0) */
+		/* conditions(end) */
+}
+
+/* Infinite loop (no exit-edge), this should not be called, but it should
+   compile fine */
+void
+mcdc021a ()
+{
+    while (1)
+	;
+}
+
+/* Computed goto can give all sorts of problems, including difficult path
+   contractions. */
+void
+mcdc021b ()
+{
+  void *op = &&dest;
+dest:
+  if (op) /* conditions(0/2) true(0) false(0) */
+	  /* conditions(end) */
+    goto * 0;
+}
+
+int __sigsetjmp ();
+
+/* This should compile, but not called. */
+void
+mcdc021c ()
+{
+  while (x) /* conditions(0/2) true(0) false(0)*/
+	    /* conditions(end) */
+     __sigsetjmp ();
+}
+
+/* If edges are not properly contracted the a && id (b) will be interpreted as
+   two independent expressions. */
+void
+mcdc021d (int a, int b, int c, int d)
+{
+    if (a && id (b)) /* conditions(1/4) true(0 1) false(0) */
+		     /* conditions(end) */
+	x = 1;
+    else if (c && id (d)) /* conditions(1/4) true(0 1) false(0) */
+			  /* conditions(end) */
+	x = 2;
+    else
+	x = 3;
+}
+
+/* Adapted from linux arch/x86/tools/relocs.c
+   With poor edge contracting this became an infinite loop. */
+void
+mcdc022a (int a, int b)
+{
+    for (int i = 0; i < 5; i++) /* conditions(2/2) */
+    {
+	x = i;
+	for (int j = i; j < 5; j++) /* conditions(2/2) */
+	{
+	    if (id (id (a)) || id (b)) /* conditions(3/4) true(0) */
+				       /* conditions(end) */
+		continue;
+	    b = inv(b);
+	}
+    }
+}
+
+int
+mcdc022b (int a)
+{
+    int devt;
+    if (a) /* conditions(2/2) */
+    {
+	x = a * 2;
+	if (x != a / 10 || x != a % 10) /* conditions(1/4) true(1) false(0 1) */
+					/* conditions(end) */
+	    return 0;
+    } else {
+	devt = id (a);
+	if (devt) /* conditions(1/2) true(0) */
+		  /* conditions(end) */
+	    return 0;
+    }
+
+    return devt;
+}
+
+/* Adapted from linux arch/x86/events/intel/ds.c
+
+   It broken sorting so that the entry block was not the first node after
+   sorting. */
+void
+mcdc022c (int a)
+{
+    if (!a) /* conditions(2/2) */
+	return;
+
+    for (int i = 0; i < 5; i++) /* conditions(2/2) */
+    {
+	if (id (a + i) || inv (a - 1)) /* conditions(1/4) false(0 1) true(1) */
+				       /* conditions(end) */
+	    x = a + i;
+	if (inv (a)) /* conditions(1/2) true(0) */
+		     /* conditions(end) */
+	    break;
+    }
+}
+
+void
+mcdc022d (int a)
+{
+    int i;
+    for (i = 0; i < id (a); i++) /* conditions(1/2) false(0) */
+    {
+	if (!inv (a)) /* conditions(1/2) false(0)*/
+		      /* conditions(end) */
+	    break;
+    }
+
+    if (i < a) /* conditions(1/2) false(0) */
+	       /* conditions(end) */
+	x = a + 1;
+}
+
+/* 023 specifically tests that masking works correctly, which gets complicated
+   fast with a mix of operators and deep subexpressions.  These tests violates
+   the style guide slightly to emphasize the nesting.  They all share the same
+   implementation and only one input is given to each function to obtain clean
+   coverage results. */
+void
+mcdc023a (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    // [a m n] = 0, [b, ...] = 1
+    // a is masked by b and the remaining terms should be short circuited
+    if (/* conditions(1/24) true(0 2 3 4 5 6 7 8 9 10 11) false(0 1 2 3 4 5 6 7 8 9 10 11) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc023b (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    // [a b d h] = 0, [c, ...] = 1
+    // h = 0 => false but does not mask (a || b) or (c && d). d = 0 masks c.
+    if (/* conditions(4/24) true(0 1 2 3 4 5 6 7 8 9 10 11) false(2 4 5 6 8 9 10 11) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc023c (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    /* [m n a b] = 0, [...] = 1
+       n,m = 0 should mask all other terms than a, b */
+    if (/* conditions(4/24) true(0 1 2 3 4 5 6 7 8 9 10 11) false(2 3 4 5 6 7 8 9) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc023d (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    /* [a b] = 0, [h, ...] = 1
+       n,m = 0 should mask all other terms than a, b */
+    if (/* conditions(4/24) true(0 1 2 3 4 5 6 7 8 9 10 11) false(2 3 4 5 6 7 10 11) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc023e (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    /* [a b d] = 0, [c h, ...] = 1
+       h = 1 should mask c, d, leave other terms intact.
+       If [k l m n] were false then h itself would be masked.
+       [a b] are masked as collateral by [m n]. */
+    if (/* conditions(5/24) true(0 1 2 3 6 9 11) false(0 1 2 3 4 5 6 7 8 9 10 11) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc023f (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    /* [a b c f g] = 0, [e, ...] = 1
+       [f g] = 0 should mask e, leave [c d] intact. */
+    if (/* conditions(5/24) true(0 1 2 3 4 5 6 7 8 9 10 11) false(3 4 7 8 9 10 11) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc023g (int a, int b, int c, int d, int e, int f, int g, int h, int i, int k,
+	  int l, int m, int n)
+{
+    /* [a b d f g] = 0, [e c, ...] = 1
+       Same as 023f but with [c d] flipped so d masks c rather than c
+       short-circuits.  This should not be lost. */
+    if (/* conditions(5/24) true(0 1 2 3 4 5 6 7 8 9 10 11) false(2 4 7 8 9 10 11) */
+	/* conditions(end) */
+	   (a || b)
+	|| (   ((c && d) || (e && (f || g) && h))
+	    && (k || l)
+	    && (m || n)))
+	x = a + b;
+    else
+	x = b + c;
+}
+
+void
+mcdc024a (int a, int b)
+{
+    if (a && b) /* conditions(1/4) true(0 1) false(1) */
+		/* conditions(end) */
+    {
+label1:
+	x = 1;
+    }
+    else
+    {
+	x = 2;
+    }
+
+    if (a || b) /* conditions(2/4) true(0 1) */
+		/* conditions(end) */
+    {
+label2:
+	x = 1;
+    }
+    else
+    {
+	x = 2;
+    }
+}
+
+void
+mcdc024b (int a, int b)
+{
+
+    if (a && b) /* conditions(1/4) true(0 1) false(1) */
+		/* conditions(end) */
+    {
+	x = 1;
+    }
+    else
+    {
+label1:
+	x = 2;
+    }
+
+    if (a || b) /* conditions(2/4) true(0 1) */
+		/* conditions(end) */
+    {
+	x = 1;
+    }
+    else
+    {
+label2:
+	x = 2;
+    }
+}
+
+void
+mcdc024c (int a, int b)
+{
+    if (a && b) /* conditions(1/4) true(0 1) false(1) */
+		/* conditions(end) */
+    {
+label1:
+	x = 1;
+    }
+    else
+    {
+label2:
+	x = 2;
+    }
+
+    if (a || b) /* conditions(2/4) true(0 1) */
+		/* conditions(end) */
+    {
+label3:
+	x = 1;
+    }
+    else
+    {
+label4:
+	x = 2;
+    }
+}
+
+int main ()
+{
+    mcdc001a (0, 1);
+
+    mcdc001b (0, 1);
+    mcdc001b (0, 0);
+
+    mcdc001c (0, 1);
+    mcdc001c (0, 0);
+    mcdc001c (1, 1);
+
+    mcdc001d (1, 1, 1);
+    mcdc001d (0, 1, 0);
+
+    mcdc002a (1, 0);
+
+    mcdc002b (1, 0);
+    mcdc002b (1, 1);
+
+    mcdc002c (0, 0);
+    mcdc002c (1, 1);
+    mcdc002c (1, 0);
+
+    mcdc002d (1, 1, 1);
+    mcdc002d (1, 0, 0);
+
+    mcdc003a (0, 0);
+    mcdc003a (1, 0);
+
+    mcdc004a (0);
+    mcdc004b (0);
+    mcdc004b (1);
+    mcdc004c (1);
+
+    mcdc004d (0, 0, 0);
+    mcdc004d (1, 1, 1);
+
+    mcdc004e (0, 0, 0);
+    mcdc004e (1, 1, 1);
+
+    mcdc005a (1, 0, 1);
+
+    mcdc005b (1, 1, 0, 0);
+    mcdc005b (1, 0, 0, 0);
+
+    mcdc005c (0, 1, 1, 0);
+
+    mcdc005d (1, 0, 0, 0);
+
+    mcdc006a (0, 0, 0, 0, 0);
+    mcdc006a (1, 0, 0, 0, 0);
+    mcdc006a (1, 1, 1, 0, 0);
+
+    mcdc006b (0, 0, 0);
+    mcdc006b (1, 0, 0);
+    mcdc006b (1, 1, 0);
+    mcdc006b (1, 1, 1);
+
+    mcdc006c (0, 0, 0);
+    mcdc006c (1, 0, 0);
+    mcdc006c (1, 1, 0);
+    mcdc006c (1, 1, 1);
+
+    mcdc007a (0, 0, 0, 0);
+    mcdc007a (1, 0, 0, 0);
+    mcdc007a (0, 0, 1, 0);
+
+    mcdc007b (0, 0, 0);
+    mcdc007b (0, 1, 1);
+    mcdc007b (1, 0, 1);
+
+    mcdc007c (0, 0, 0);
+    mcdc007c (0, 1, 1);
+    mcdc007c (1, 0, 1);
+
+    mcdc008a (0);
+
+    mcdc008b (0);
+
+    mcdc008c (0);
+    mcdc008c (1);
+
+    mcdc008d (0, 0, 0, 0);
+    mcdc008d (1, 0, 0, 0);
+    mcdc008d (1, 0, 1, 0);
+    mcdc008d (1, 0, 1, 1);
+    mcdc008d (1, 1, 1, 1);
+
+    mcdc009a (0, 0);
+    mcdc009a (1, 1);
+
+    mcdc010a (0, 0);
+    mcdc010a (0, 9);
+    mcdc010a (2, 1);
+
+    mcdc010b ();
+
+    mcdc010c (1);
+
+    mcdc011a (0, 0, 0);
+    mcdc011a (1, 1, 0);
+    mcdc011a (1, 0, 1);
+
+    mcdc012a (0, 0, 0);
+    mcdc012a (0, 1, 1);
+
+    mcdc013a (0, 0, 0);
+    mcdc013a (0, 0, 1);
+    mcdc013a (0, 1, 0);
+    mcdc013a (0, 1, 1);
+    mcdc013a (1, 0, 0);
+    mcdc013a (1, 0, 1);
+    mcdc013a (1, 1, 0);
+    mcdc013a (1, 1, 1);
+
+    mcdc014a ();
+
+    mcdc015a (0, 0);
+    mcdc015a (1, 0);
+
+    mcdc015b (0, 0);
+    mcdc015b (0, 1);
+    mcdc015b (6, 1);
+
+    mcdc015c (0, 0);
+    mcdc015c (0, 5);
+    mcdc015c (6, 1);
+
+    mcdc016a (5, 5);
+
+    mcdc016b (5, 5);
+    mcdc016b (6, 5);
+
+    mcdc016c (5, 5);
+
+    mcdc016d (1, 0);
+
+    mcdc017a (0);
+    mcdc017a (2);
+
+    mcdc017b (2, 0);
+    mcdc017b (0, 1);
+
+    mcdc017c (1, 1);
+
+    mcdc018a (0, 0, 1, 1, 0, 0, 0, 0);
+    mcdc018a (0, 1, 0, 0, 0, 0, 1, -2);
+    mcdc018a (0, 6, 0, 0, 0, 0, 1, -2);
+    mcdc018a (0, 6, 0, 0, 0, 0, 1, -2);
+    mcdc018a (0, 0, 0, 1, 0, 1, 1, 0);
+    mcdc018a (1, 0, 0, 0, 1, 1, 0, 0);
+
+    mcdc018b (1, 0, 0);
+    mcdc018b (1, 1, 0);
+
+    mcdc018c (1, 1);
+
+    mcdc019a ();
+
+    mcdc020a (0);
+    mcdc020a (1);
+
+    mcdc020b (0, 0);
+    mcdc020b (1, 0);
+
+    mcdc020c (0, 1);
+    mcdc020c (1, 1);
+
+    mcdc021d (1, 0, 1, 0);
+
+    mcdc022a (0, 0);
+
+    mcdc022b (0);
+    mcdc022b (1);
+
+    mcdc022c (0);
+    mcdc022c (1);
+
+    mcdc022d (1);
+
+    mcdc023a (0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1);
+    mcdc023b (0, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1);
+    mcdc023c (0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0);
+    mcdc023d (0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1);
+    mcdc023e (0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1);
+    mcdc023f (0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1);
+    mcdc023g (0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1);
+
+    mcdc024a (0, 0);
+    mcdc024b (0, 0);
+    mcdc024c (0, 0);
+}
+
+/* { dg-final { run-gcov conditions { --conditions gcov-19.c } } } */
diff --git a/gcc/testsuite/gcc.misc-tests/gcov-20.c b/gcc/testsuite/gcc.misc-tests/gcov-20.c
new file mode 100644
index 00000000000..847dae495db
--- /dev/null
+++ b/gcc/testsuite/gcc.misc-tests/gcov-20.c
@@ -0,0 +1,22 @@
+/* { dg-options "-fprofile-conditions -ftest-coverage -fprofile-update=atomic" } */
+/* { dg-do run { target native } } */
+
+/* some side effect to stop branches from being pruned */
+int x = 0;
+
+void
+conditions_atomic001 (int a, int b)
+{
+    if (a || b) /* conditions(1/4) true(0) false(0 1) */
+		/* conditions(end) */
+	x = 1;
+    else
+	x = 2;
+}
+
+int main ()
+{
+    conditions_atomic001 (0, 1);
+}
+
+/* { dg-final { run-gcov conditions { --conditions gcov-20.c } } } */
diff --git a/gcc/testsuite/gcc.misc-tests/gcov-21.c b/gcc/testsuite/gcc.misc-tests/gcov-21.c
new file mode 100644
index 00000000000..978be3276a2
--- /dev/null
+++ b/gcc/testsuite/gcc.misc-tests/gcov-21.c
@@ -0,0 +1,16 @@
+/* { dg-options "-fprofile-conditions" } */
+
+/* https://gcc.gnu.org/pipermail/gcc-patches/2022-April/592927.html */
+char trim_filename_name;
+int r;
+
+void trim_filename() {
+    if (trim_filename_name)
+	r = 123;
+    while (trim_filename_name)
+	;
+}
+
+int main ()
+{
+}
diff --git a/gcc/testsuite/lib/gcov.exp b/gcc/testsuite/lib/gcov.exp
index 9d5b2cdb86b..69168d67d03 100644
--- a/gcc/testsuite/lib/gcov.exp
+++ b/gcc/testsuite/lib/gcov.exp
@@ -174,6 +174,184 @@ proc verify-branches { testname testcase file } {
     return $failed
 }
 
+#
+# verify-conditions -- check that conditions are checked as expected
+#
+# TESTNAME is the name of the test, including unique flags.
+# TESTCASE is the name of the test file.
+# FILE is the name of the gcov output file.
+#
+# Checks are based on comments in the source file. Condition coverage comes
+# with with two types of output, a summary and a list of the uncovered
+# conditions. Both must be checked to pass the test
+#
+# To check for conditions, add a comment the line of a conditional:
+# /* conditions(n/m) true(0 1) false(1) */
+#
+# where n/m are the covered and total conditions in the expression. The true()
+# and false() take the indices expected *not* covered.
+#
+# This means that all coverage statements should have been seen:
+# /* conditions(end) */
+#
+# If all conditions are covered i.e. n == m, then conditions(end) can be
+# omitted. If either true() or false() are empty they can be omitted too.
+#
+# C++ can insert conditionals in the CFG that are not present in source code.
+# These must be manually suppressed since unexpected and unhandled conditions
+# are an error (to help combat regressions). Output can be suppressed with
+# conditions(suppress) and conditions(end). suppress should usually be on a
+# closing brace.
+#
+# Some expressions, when using unnamed temporaries as operands, will have
+# destructors in expressions. The coverage of the destructor will be reported
+# on the same line as the expression itself, but suppress() would also swallow
+# the expected tested-for messages. To handle these, use the destructor() [1]
+# which will suppress everything from and including the second "conditions
+# covered".
+#
+# [1] it is important that the destructor() is *on the same line* as the
+#     conditions(m/n)
+proc verify-conditions { testname testcase file } {
+    set failed 0
+    set suppress 0
+    set destructor 0
+    set should ""
+    set shouldt ""
+    set shouldf ""
+    set shouldall ""
+    set fd [open $file r]
+    set n 0
+    set keywords {"end" "suppress"}
+    while {[gets $fd line] >= 0} {
+	regexp "^\[^:\]+: *(\[0-9\]+):" "$line" all n
+	set prefix "$testname line $n"
+
+	if {![regexp "condition" $line]} {
+	    continue
+	}
+
+	# Missing coverage for both true and false will cause a failure, but
+	# only count it once for the report.
+	set ok 1
+	if [regexp {conditions *\(([0-9a-z/]+)\)} "$line" all e] {
+	    # *Very* coarse sanity check: conditions() should either be a
+	    # keyword or n/m, anything else means a buggy test case. end is
+	    # optional for cases where all conditions are covered, since it
+	    # only expects a single line of output.
+	    if {([lsearch -exact $keywords $e] >= 0 || [regexp {\d+/\d+} "$e"]) == 0} {
+		fail "$prefix: expected conditions (n/m), (suppress) or (end); was ($e)"
+		incr failed
+		continue
+	    }
+
+	    # Any keyword means a new context. Set the error flag if not all
+	    # expected output has been seen, and reset the state.
+
+	    if {[llength $shouldt] != 0} {
+		fail "$prefix: expected 'not covered (true)' for terms: $shouldt"
+		set ok 0
+	    }
+
+	    if {[llength $shouldf] != 0} {
+		fail "$prefix: expected 'not covered (false)' for terms: $shouldf"
+		set ok 0
+	    }
+
+	    if {$shouldall ne ""} {
+		fail "$prefix: coverage summary not found; expected $shouldall"
+		set ok 0
+	    }
+
+	    set suppress 0
+	    set destructor 0
+	    set should ""
+	    set shouldt ""
+	    set shouldf ""
+	    set shouldall ""
+	    set newt ""
+	    set newf ""
+
+	    if [regexp {destructor\(\)} "$line"] {
+		set destructor 1
+	    }
+
+	    if [regexp {(\d+)/(\d+)} "$e" all i k] {
+		regexp {true\(([0-9 ]+)\)}  "$line" all newt
+		regexp {false\(([0-9 ]+)\)} "$line" all newf
+
+		# Sanity check - if the true() and false() vectors should have
+		# m-n elements to cover all uncovered conditions. Because of
+		# masking it can sometimes be surprising what terms are
+		# independent, so this makes for more robust test at the cost
+		# of being slightly more annoying to write.
+		set nterms [expr [llength $newt] + [llength $newf]]
+		set nexpected [expr {$k - $i}]
+		if {$nterms != $nexpected} {
+		    fail "$prefix: expected $nexpected uncovered terms; got $nterms"
+		    set ok 0
+		}
+		set shouldall $e
+		set shouldt $newt
+		set shouldf $newf
+	    } elseif {$e == "end"} {
+		# no-op - state has already been reset, and errors flagged
+	    } elseif {$e == "suppress"} {
+		set suppress 1
+	    } else {
+		# this should be unreachable, 
+		fail "$prefix: unhandled control ($e), should be unreachable"
+		set ok 0
+	    }
+	} elseif {$suppress == 1} {
+	    # ignore everything in a suppress block. C++ especially can insert
+	    # conditionals in exceptions and destructors which would otherwise
+	    # be considered unhandled.
+	    continue
+	} elseif [regexp {condition +(\d+) not covered \((.*)\)} "$line" all cond condv] {
+	    foreach v {true false} {
+		if [regexp $v $condv] {
+		    if {"$v" == "true"} {
+			set should shouldt
+		    } else {
+			set should shouldf
+		    }
+
+		    set i [lsearch [set $should] $cond]
+		    if {$i != -1} {
+			set $should [lreplace [set $should] $i $i]
+		    } else {
+			fail "$testname line $n: unexpected uncovered term $cond ($v)"
+			set ok 0
+		    }
+		}
+	    }
+	} elseif [regexp {condition outcomes covered (\d+/\d+)} "$line" all cond] {
+	    # the destructor-generated "conditions covered" lines will be
+	    # written after all expression-related output. Handle these by
+	    # turning on suppression if the destructor-suppression is
+	    # requested.
+	    if {$shouldall == "" && $destructor == 1} {
+		set suppress 1
+		continue
+	    }
+
+	    if {$cond == $shouldall} {
+		set shouldall ""
+	    } else {
+		fail "$testname line $n: unexpected summary $cond"
+		set ok 0
+	    }
+	}
+
+	if {$ok != 1} {
+	    incr failed
+	}
+    }
+    close $fd
+    return $failed
+}
+
 #
 # verify-calls -- check that call return percentages are as expected
 #
@@ -321,6 +499,7 @@ proc run-gcov { args } {
     set gcov_args ""
     set gcov_verify_calls 0
     set gcov_verify_branches 0
+    set gcov_verify_conditions 0
     set gcov_verify_lines 1
     set gcov_verify_intermediate 0
     set gcov_remove_gcda 0
@@ -331,10 +510,13 @@ proc run-gcov { args } {
 	  set gcov_verify_calls 1
 	} elseif { $a == "branches" } {
 	  set gcov_verify_branches 1
+	} elseif { $a == "conditions" } {
+	  set gcov_verify_conditions 1
 	} elseif { $a == "intermediate" } {
 	  set gcov_verify_intermediate 1
 	  set gcov_verify_calls 0
 	  set gcov_verify_branches 0
+	  set gcov_verify_conditions 0
 	  set gcov_verify_lines 0
 	} elseif { $a == "remove-gcda" } {
 	  set gcov_remove_gcda 1
@@ -404,6 +586,11 @@ proc run-gcov { args } {
     } else {
 	set bfailed 0
     }
+    if { $gcov_verify_conditions } {
+	set cdfailed [verify-conditions $testname $testcase $testcase.gcov]
+    } else {
+	set cdfailed 0
+    }
     if { $gcov_verify_calls } {
 	set cfailed [verify-calls $testname $testcase $testcase.gcov]
     } else {
@@ -418,12 +605,12 @@ proc run-gcov { args } {
 
     # Report whether the gcov test passed or failed.  If there were
     # multiple failures then the message is a summary.
-    set tfailed [expr $lfailed + $bfailed + $cfailed + $ifailed]
+    set tfailed [expr $lfailed + $bfailed + $cdfailed + $cfailed + $ifailed]
     if { $xfailed } {
 	setup_xfail "*-*-*"
     }
     if { $tfailed > 0 } {
-	fail "$testname gcov: $lfailed failures in line counts, $bfailed in branch percentages, $cfailed in return percentages, $ifailed in intermediate format"
+	fail "$testname gcov: $lfailed failures in line counts, $bfailed in branch percentages, $cdfailed in condition/decision, $cfailed in return percentages, $ifailed in intermediate format"
 	if { $xfailed } {
 	    clean-gcov $testcase
 	}
diff --git a/gcc/tree-profile.cc b/gcc/tree-profile.cc
index 2beb49241f2..766b269f661 100644
--- a/gcc/tree-profile.cc
+++ b/gcc/tree-profile.cc
@@ -58,6 +58,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "alloc-pool.h"
 #include "symbol-summary.h"
 #include "symtab-thunks.h"
+#include "cfganal.h"
+#include "cfgloop.h"
 
 static GTY(()) tree gcov_type_node;
 static GTY(()) tree tree_interval_profiler_fn;
@@ -73,6 +75,1046 @@ static GTY(()) tree ic_tuple_var;
 static GTY(()) tree ic_tuple_counters_field;
 static GTY(()) tree ic_tuple_callee_field;
 
+namespace
+{
+/* Some context and reused instances between function calls.  Large embedded
+   buffers are used to up-front request enough memory for most programs and
+   merge them into a single allocation at the cost of using more memory in the
+   average case.  Some numbers from linux v5.13 which is assumed to be a
+   reasonably diverse code base: 75% of the functions in linux have less than
+   16 nodes in the CFG and approx 2.5% have more than 64 nodes.  The functions
+   that go beyond a few dozen nodes tend to be very large (>100) and so 64
+   seems like a good balance.
+
+   This is really just a performance balance of the cost of allocation and
+   wasted memory.  */
+struct conds_ctx
+{
+    /* Bitmap of the processed blocks.  Bit n set means basic_block->index has
+       been processed either explicitly or as a part of an expression.  */
+    auto_sbitmap marks;
+
+    /* This is both a reusable shared allocation which is also used to return
+       single expressions, which means it for most code should only hold a
+       couple of elements.  */
+    auto_vec<basic_block, 32> blocks;
+
+    /* Map from basic_block->index to an ordering so that for a single
+       expression (a || b && c) => index_map[a] < index_map[b] < index_map[c].
+       The values do not have to be consecutive and can be interleaved by
+       values from other expressions, so comparisons only make sense for blocks
+       that belong to the same expression.  */
+    auto_vec<int, 64> index_map;
+
+    /* Pre-allocate bitmaps and vectors for per-function book keeping.  This is
+       pure instance reuse and the bitmaps carry no data between function
+       calls.  */
+    auto_vec<basic_block, 64> B1;
+    auto_vec<basic_block, 64> B2;
+    auto_sbitmap G1;
+    auto_sbitmap G2;
+    auto_sbitmap G3;
+
+    explicit conds_ctx (unsigned size) noexcept (true) : marks (size),
+    G1 (size), G2 (size), G3 (size)
+    {
+	bitmap_clear (marks);
+    }
+
+    /* Mark a node as processed so nodes are not processed twice for example in
+       loops, gotos.  */
+    void mark (const basic_block b) noexcept (true)
+    {
+	gcc_assert (!bitmap_bit_p (marks, b->index));
+	bitmap_set_bit (marks, b->index);
+    }
+
+    /* Mark nodes as processed so they are not processed twice.  */
+    void mark (const vec<basic_block>& bs) noexcept (true)
+    {
+	for (const basic_block b : bs)
+	    mark (b);
+    }
+
+    /* Check if all nodes are marked.  A successful run should visit & mark
+       every reachable node exactly once.  */
+    bool all_marked (const vec<basic_block>& reachable) const noexcept (true)
+    {
+	for (const basic_block b : reachable)
+	    if (!bitmap_bit_p (marks, b->index))
+		return false;
+	return true;
+    }
+};
+
+/* Only instrument terms with fewer than number of bits in a (wide) gcov
+   integer, which is probably 64.  The algorithm itself does not impose this
+   limitation, but it makes for a simpler implementation.
+
+   * Allocating the output data structure (coverage_counter_alloc ()) can
+     assume pairs of gcov_type_unsigned and not use a separate length field.
+   * A pair gcov_type_unsigned can be used as accumulators.
+   * Updating accumulators is can use the bitwise operations |=, &= and not
+     custom operators that work for arbitrary-sized bit-sets.
+
+   Most real-world code should be unaffected by this, but it is possible
+   (especially for generated code) to exceed this limit.  */
+#define CONDITIONS_MAX_TERMS (sizeof (gcov_type_unsigned) * BITS_PER_UNIT)
+#define EDGE_CONDITION (EDGE_TRUE_VALUE | EDGE_FALSE_VALUE)
+
+/* Compare two basic blocks by their order in the expression i.e. for (a || b)
+   then cmp_index_map (a, b, ...) < 0.  The result is undefined if lhs, rhs
+   belong to different expressions.  */
+int
+cmp_index_map (const void *lhs, const void *rhs, void *index_map)
+{
+    const_basic_block l = *(const basic_block*) lhs;
+    const_basic_block r = *(const basic_block*) rhs;
+    const vec<int>* im = (const vec<int>*) index_map;
+    return (*im)[l->index] - (*im)[r->index];
+}
+
+/* Find the index of needle in blocks; return -1 if not found.  This has two
+   uses, sometimes for the index and sometimes for set member c hecks.  Sets are
+   typically very small (number of conditions, >8 is uncommon) so linear search
+   should be very fast.  */
+int
+index_of (const basic_block needle, array_slice<basic_block> blocks)
+{
+    for (size_t i = 0; i < blocks.size (); i++)
+	if (blocks[i] == needle)
+	    return int (i);
+    return -1;
+}
+
+/* Returns true if this is a conditional node, i.e. it has outgoing true and
+   false edges.  */
+bool
+block_conditional_p (const basic_block b)
+{
+    unsigned t = 0;
+    unsigned f = 0;
+    for (edge e : b->succs)
+    {
+	t |= (e->flags & EDGE_TRUE_VALUE);
+	f |= (e->flags & EDGE_FALSE_VALUE);
+    }
+    return t && f;
+}
+
+/* Check if the edge is a conditional.  */
+bool
+edge_conditional_p (const edge e)
+{
+    return e->flags & EDGE_CONDITION;
+}
+
+/* Special cases of the single_*_p and single_*_edge functions in basic-block.h
+   that don't consider exception handling or other complex edges.  This helps
+   create a view of the CFG with only normal edges - if a basic block has both
+   an outgoing fallthrough and exceptional edge [1], it should be considered a
+   single-successor.
+
+   [1] if this is not possible, these functions can be removed and replaced by
+       their basic-block.h cousins.  */
+bool
+single (const vec<edge, va_gc> *edges)
+{
+    int n = EDGE_COUNT (edges);
+    if (n == 0)
+	return false;
+
+    for (edge e : edges)
+	if (e->flags & EDGE_COMPLEX)
+	    n -= 1;
+
+    return n == 1;
+}
+
+/* Get the single, non-complex edge.  Behavior is undefined edges have more
+   than 1 non-complex edges.  */
+edge
+single_edge (const vec<edge, va_gc> *edges)
+{
+    for (edge e : edges)
+    {
+	if (e->flags & EDGE_COMPLEX)
+	    continue;
+	return e;
+    }
+    return NULL;
+}
+
+/* Sometimes, for example with function calls and C++ destructors, the CFG gets
+   extra nodes that are essentially single-entry-single-exit in the middle of
+   boolean expressions.  For example:
+
+      x || can_throw (y)
+
+               A
+              /|
+             / |
+            B  |
+            |  |
+            C  |
+           / \ |
+          /   \|
+         F     T
+
+   Without the extra node inserted by the function + exception it becomes a
+   proper 2-term graph, not 2 single-term graphs.
+
+               A
+              /|
+             C |
+            / \|
+           F   T
+
+   contract_edge ignores the series of intermediate nodes and makes a virtual
+   edge A -> C without having to construct a new simplified CFG explicitly.  It
+   gets more complicated as non-conditional edges is how the body of the
+   then/else blocks are separated from the boolean expression, so only edges
+   that are inserted because of function calls in the expression itself must be
+   merged.
+
+   Only chains of single-exit single-entry nodes that end with a condition
+   should be contracted.  */
+edge
+contract_edge (edge e)
+{
+    edge source = e;
+    while (true)
+    {
+	basic_block dest = e->dest;
+	if (!single (dest->preds))
+	    return source;
+	if (e->flags & EDGE_DFS_BACK)
+	    return source;
+	if (block_conditional_p (dest))
+	    return e;
+
+	e = single_edge (dest->succs);
+	if (!e)
+	    return source;
+    }
+}
+
+/* This is the predecessor dual of contract_edge; it collapses the predecessor
+   blocks between two operands in a boolean expression.  */
+edge
+contract_edge_up (edge e)
+{
+    while (true)
+    {
+	basic_block src = e->src;
+	if (edge_conditional_p (e))
+	    return e;
+	if (!single (src->preds))
+	    return e;
+	e = single_edge (src->preds);
+    }
+}
+
+/* "Undo" an edge split.  Sometimes the sink of a boolean expression will be
+   split into multiple blocks to accurately track line coverage, for example
+   when there is a goto-label at the top of the then/else block:
+
+    if (a && b)
+    {
+	l1:
+	...
+    }
+    else
+    {
+	l2:
+	...
+    }
+
+    and the corresponding CFG where a1 and b1 are created in edge splits to the
+    same destination (F):
+
+    a
+    |\
+    | a1
+    b  \
+    |\  |
+    | b1|
+    |  \|
+    T   F
+
+    This function recognizes this shape and returns the "merges" the split
+    outcome block by returning their common successor.  In all other cases it is
+    the identity function.  */
+basic_block
+merge_split_outcome (basic_block b)
+{
+    if (!single (b->succs))
+	return b;
+    if (!single (b->preds))
+	return b;
+
+    const unsigned flag = single_edge (b->preds)->flags & EDGE_CONDITION;
+    if (!flag)
+	return b;
+
+    edge e = single_edge (b->succs);
+    for (edge pred : e->dest->preds)
+    {
+	if (!single (pred->src->preds))
+	    return b;
+	if (!(single_edge (pred->src->preds)->flags & flag))
+	    return b;
+    }
+    return e->dest;
+}
+
+
+/* Find the set {ancestors (p) intersect G} where ancestors is the recursive
+   set of predecessors for p.  Limiting to the ancestors that are also in G
+   (see cond_reachable_from) and by q is an optimization as ancestors outside G
+   have no effect when isolating expressions.
+
+   dfs_enumerate_from () does not work as the filter function needs edge
+   information and dfs_enumerate_from () only considers blocks.  */
+void
+ancestors_of (basic_block p, basic_block q, const sbitmap G, sbitmap ancestors)
+{
+    if (!bitmap_bit_p (G, p->index))
+	return;
+
+    bitmap_set_bit (ancestors, p->index);
+    bitmap_set_bit (ancestors, q->index);
+    if (p == q)
+	return;
+
+    auto_vec<basic_block, 16> stack;
+    stack.safe_push (p);
+
+    while (!stack.is_empty ())
+    {
+	basic_block b = stack.pop ();
+	if (single (b->preds))
+	{
+	    edge e = single_edge (b->preds);
+	    e = contract_edge_up (e);
+	    b = e->dest;
+	}
+
+	for (edge e : b->preds)
+	{
+	    basic_block src = e->src;
+	    if (bitmap_bit_p (ancestors, e->src->index))
+		continue;
+	    if (!bitmap_bit_p (G, e->src->index))
+		continue;
+	    bitmap_set_bit (ancestors, src->index);
+	    stack.safe_push (src);
+	}
+    }
+}
+
+/* A simple struct for storing/returning outcome block pairs.  Either both
+   blocks are set or both are NULL.  */
+struct outcomes
+{
+    basic_block t = NULL;
+    basic_block f = NULL;
+
+    operator bool () const noexcept (true)
+    {
+	return t && f;
+    }
+};
+
+/* Get the true/false successors of a basic block.  If b is not a conditional
+   block both edges are NULL.  */
+outcomes
+conditional_succs (const basic_block b)
+{
+    outcomes c;
+    for (edge e : b->succs)
+    {
+	if (e->flags & EDGE_TRUE_VALUE)
+	    c.t = merge_split_outcome (e->dest);
+	if (e->flags & EDGE_FALSE_VALUE)
+	    c.f = merge_split_outcome (e->dest);
+    }
+
+    gcc_assert ((c.t && c.f) || (!c.t && !c.f));
+    return c;
+}
+
+/* Get the index or offset of a conditional flag, 0 for true and 1 for false.
+   These indices carry no semantics but must be consistent as they are used to
+   index into data structures in code generation and gcov.  */
+unsigned
+condition_index (unsigned flag)
+{
+    return (flag & EDGE_CONDITION) == EDGE_TRUE_VALUE ? 0 : 1;
+}
+
+/* Compute the masking vector.
+
+   Masking and short circuiting are deeply connected - masking occurs when
+   control flow reaches a state that is also reachable with short circuiting.
+   In fact, masking corresponds to short circuiting in the CFG for the reversed
+   expression.  This means we can find the limits, the last term in preceeding
+   subexpressions, by following the edges that short circuit to the same
+   outcome.
+
+   In the simplest case a || b:
+
+   a
+   |\
+   | b
+   |/ \
+   T   F
+
+   T has has multiple incoming edges and is the outcome of a short circuit,
+   with top = a, bot = b.  The top node (a) is masked when the edge (b, T) is
+   taken.
+
+   The names "top" and "bot" refer to a pair of nodes with a shared
+   destination.  The top is always the node corresponding to the left-most
+   operand of the two it holds that index_map[top] < index_map[bot].
+
+   Now consider (a && b) || (c && d) and its masking vectors:
+
+   a
+   |\
+   b \
+   |\|
+   | c
+   | |\
+   | d \
+   |/ \|
+   T   F
+
+   a[0] = {}
+   a[1] = {}
+   b[0] = {a}
+   b[1] = {}
+   c[0] = {}
+   c[1] = {}
+   d[0] = {c}
+   d[1] = {a,b}
+
+   Note that 0 and 1 are indices and not boolean values - a[0] is the index in
+   the masking vector when a takes the true edge.
+
+   b[0] and d[0] are identical to the a || b example, and d[1] is the bot in
+   the triangle [d, b] -> T.  b is the top node in the [d, b] relationship and
+   last term in (a && b).  To find the other terms masked we use the fact that
+   all nodes in an expression have outgoing edges to either the outcome or some
+   other node in the expression.  The "bot" node is also the last term in a
+   masked subexpression, so the problem becomes finding the subgraph where all
+   paths end up in the successors to bot.
+
+   We find the terms by marking the outcomes (in this case c, T) and walk the
+   predecessors starting at top (in this case b) and masking nodes when both
+   successors are marked.
+
+   The masking vector is represented as two bitfields per term in the
+   expression with the index corresponding to the term in the source
+   expression.  a || b && c becomes the term vector [a b c] and the masking
+   vectors [a[0] a[1] b[0] ...].  The kth bit of a masking vector is set if the
+   the kth term is masked by taking the edge.  */
+void
+masking_vectors (conds_ctx& ctx, array_slice<basic_block> blocks,
+		 array_slice<gcov_type_unsigned> masks)
+{
+    gcc_assert (blocks.is_valid ());
+    gcc_assert (!blocks.empty ());
+    gcc_assert (masks.is_valid ());
+
+    sbitmap marks = ctx.G1;
+    sbitmap expr = ctx.G2;
+    vec<basic_block>& queue = ctx.B1;
+    vec<basic_block>& body = ctx.B2;
+    const vec<int>& index_map = ctx.index_map;
+    bitmap_clear (expr);
+
+    for (const basic_block b : blocks)
+	bitmap_set_bit (expr, b->index);
+
+    /* Set up for the iteration - include two outcome nodes in the traversal and
+       ignore the leading term since it cannot mask anything.  The algorithm is
+       not sensitive to the traversal order.  */
+    body.truncate (0);
+    body.reserve (blocks.size () + 2);
+    for (const basic_block b : blocks)
+	body.quick_push (b);
+
+    outcomes out = conditional_succs (blocks.back ());
+    body.quick_push (out.t);
+    body.quick_push (out.f);
+    body[0] = body.pop ();
+
+    for (const basic_block b : body)
+    {
+	for (edge e1 : b->preds)
+	for (edge e2 : b->preds)
+	{
+	    const basic_block top = e1->src;
+	    const basic_block bot = e2->src;
+	    const unsigned cond = e1->flags & e2->flags & (EDGE_CONDITION);
+
+	    if (!cond)
+		continue;
+	    if (e1 == e2)
+		continue;
+	    if (!bitmap_bit_p (expr, top->index))
+		continue;
+	    if (!bitmap_bit_p (expr, bot->index))
+		continue;
+	    if (index_map[top->index] > index_map[bot->index])
+		continue;
+
+	    outcomes out = conditional_succs (top);
+	    gcc_assert (out);
+	    bitmap_clear (marks);
+	    bitmap_set_bit (marks, out.t->index);
+	    bitmap_set_bit (marks, out.f->index);
+	    queue.truncate (0);
+	    queue.safe_push (top);
+
+	    // The edge bot -> outcome triggers the masking
+	    const int m = 2*index_of (bot, blocks) + condition_index (cond);
+	    while (!queue.is_empty ())
+	    {
+		basic_block q = queue.pop ();
+		/* q may have been processed & completed by being added to the
+		   queue multiple times, so check that there is still work to
+		   do before continuing.  */
+		if (bitmap_bit_p (marks, q->index))
+		    continue;
+
+		outcomes succs = conditional_succs (q);
+		if (!bitmap_bit_p (marks, succs.t->index))
+		    continue;
+		if (!bitmap_bit_p (marks, succs.f->index))
+		    continue;
+
+		const int index = index_of (q, blocks);
+		gcc_assert (index != -1);
+		masks[m] |= gcov_type_unsigned (1) << index;
+		bitmap_set_bit (marks, q->index);
+
+		for (edge e : q->preds)
+		{
+		    e = contract_edge_up (e);
+		    if (!edge_conditional_p (e))
+			continue;
+		    if (e->flags & EDGE_DFS_BACK)
+			continue;
+		    if (bitmap_bit_p (marks, e->src->index))
+			continue;
+		    if (!bitmap_bit_p (expr, e->src->index))
+			continue;
+		    queue.safe_push (e->src);
+		}
+	    }
+	}
+    }
+}
+
+/* Find the nodes reachable from p by following only (possibly contracted)
+   condition edges dominated by p and ignore DFS back edges.  From a high level
+   this is partitioning the CFG into subgraphs by removing all non-condition
+   edges and selecting a single connected subgraph.  This creates a cut C = (G,
+   G') where G is the returned explicitly by this function.
+
+   It is assumed that all paths from p go through q (q post-dominates p).  p
+   must always be the first term in an expression and a condition node.
+
+   If |G| = 1 then this is a single term expression.  If |G| > 1 then either
+   this is a multi-term expression or the first block in the then/else block is
+   a conditional expression as well.
+
+   Only nodes dominated by p is added - under optimization some blocks may be
+   merged and multiple independent conditions may share the same outcome
+   (making successors misidentified as a right operands), but true right-hand
+   operands are always dominated by the first term.
+
+   The function outputs both a bitmap and a vector as both are useful to the
+   caller.  */
+void
+cond_reachable_from (basic_block p, basic_block q, sbitmap expr,
+		     vec<basic_block>& out)
+{
+    out.safe_push (p);
+    bitmap_set_bit (expr, p->index);
+    for (unsigned pos = 0; pos < out.length (); pos++)
+    {
+	for (edge e : out[pos]->succs)
+	{
+	    basic_block dest = contract_edge (e)->dest;
+	    if (dest == q)
+		continue;
+	    if (!dominated_by_p (CDI_DOMINATORS, dest, p))
+		continue;
+	    if (!block_conditional_p (dest))
+		continue;
+	    if (bitmap_bit_p (expr, dest->index))
+		continue;
+	    if (e->flags & EDGE_DFS_BACK)
+		continue;
+
+	    bitmap_set_bit (expr, dest->index);
+	    out.safe_push (dest);
+	}
+    }
+}
+
+/* Find the neighborhood of the graph G = [blocks, blocks+n), the
+   successors of nodes in G that are not also in G.  In the cut C = (G, G')
+   these are the nodes in G' with incoming edges that cross the span.  */
+void
+neighborhood (const vec<basic_block>& blocks, sbitmap G, vec<basic_block>& out)
+{
+    for (const basic_block b : blocks)
+    {
+	for (edge e : b->succs)
+	{
+	    basic_block dest = contract_edge (e)->dest;
+	    if (bitmap_bit_p (G, dest->index))
+		continue;
+	    if (!out.contains (dest))
+		out.safe_push (dest);
+	}
+    }
+
+    /* Fix the neighborhood by correcting edge splits to the outcome nodes.  */
+    for (unsigned i = 0; i != out.length (); i++)
+    {
+	basic_block prev = out[i];
+	basic_block next = merge_split_outcome (prev);
+	if (next->index != prev->index)
+	{
+	    bitmap_set_bit (G, prev->index);
+	    out[i] = next;
+	}
+    }
+}
+
+/* Find and isolate the expression starting at p.
+
+   Make a cut C = (G, G') following only condition edges.  G is a superset of
+   the expression B, but the walk may include expressions from the then/else
+   blocks if they start with conditions.  Only the subgraph B is the ancestor
+   of *both* the then/else outcome, which means B is the intersection of the
+   ancestors of the nodes in the neighborhood N(G).  */
+void
+isolate_expression (conds_ctx &ctx, basic_block p, vec<basic_block>& out)
+{
+    sbitmap expr = ctx.G1;
+    sbitmap reachable = ctx.G2;
+    sbitmap ancestors = ctx.G3;
+    bitmap_clear (expr);
+    bitmap_clear (reachable);
+
+    vec<basic_block>& G = ctx.B1;
+    vec<basic_block>& NG = ctx.B2;
+    G.truncate (0);
+    NG.truncate (0);
+
+    basic_block post = get_immediate_dominator (CDI_POST_DOMINATORS, p);
+    cond_reachable_from (p, post, reachable, G);
+    if (G.length () == 1)
+    {
+	out.safe_push (p);
+	return;
+    }
+
+    neighborhood (G, reachable, NG);
+    bitmap_copy (expr, reachable);
+
+    for (const basic_block neighbor : NG)
+    {
+	bitmap_clear (ancestors);
+	for (edge e : neighbor->preds)
+	    ancestors_of (e->src, p, reachable, ancestors);
+	bitmap_and (expr, expr, ancestors);
+    }
+
+    for (const basic_block b : G)
+	if (bitmap_bit_p (expr, b->index))
+	    out.safe_push (b);
+    out.sort (cmp_index_map, &ctx.index_map);
+}
+
+/* Emit lhs = op1 <op> op2 on edges.  This emits non-atomic instructions and
+   should only be used on the local accumulators.  */
+void
+emit_bitwise_op (edge e, tree lhs, tree op1, tree_code op, tree op2)
+{
+    tree tmp;
+    gassign *read;
+    gassign *bitw;
+    gimple *write;
+
+    tmp = make_temp_ssa_name (gcov_type_node, NULL, "__conditions_tmp");
+    read = gimple_build_assign (tmp, op1);
+    tmp = make_temp_ssa_name (gcov_type_node, NULL, "__conditions_tmp");
+    bitw = gimple_build_assign (tmp, op, gimple_assign_lhs (read), op2);
+    write = gimple_build_assign (lhs, gimple_assign_lhs (bitw));
+
+    gsi_insert_on_edge (e, read);
+    gsi_insert_on_edge (e, bitw);
+    gsi_insert_on_edge (e, write);
+}
+
+/* Visitor for make_index_map.  */
+void
+make_index_map_visit (basic_block b, vec<basic_block>& L, vec<int>& marks)
+{
+    if (marks[b->index])
+	return;
+
+    for (edge e : b->succs)
+	if (!(e->flags & EDGE_DFS_BACK))
+	    make_index_map_visit (e->dest, L, marks);
+
+    marks[b->index] = 1;
+    L.quick_push (b);
+}
+
+/* Find a topological sorting of the blocks in a function so that left operands
+   are before right operands including subexpressions.  Sorting on block index
+   does not guarantee this property and the syntactical order of terms is very
+   important to the condition coverage.  The sorting algorithm is from Cormen
+   et al (2001) but with back-edges ignored and thus there is no need for
+   temporary marks (for cycle detection).
+
+   It is important to select unvisited nodes in DFS order to ensure the
+   roots/leading terms of boolean expressions are visited first (the other
+   terms being covered by the recursive step), but the visiting order of
+   individual boolean expressions carries no significance.
+
+   For the expression (a || (b && c) || d) the blocks should be [a b c d].  */
+void
+make_index_map (const vec<basic_block>& blocks, int max_index,
+		vec<basic_block>& L, vec<int>& index_map)
+{
+    L.truncate (0);
+    L.reserve (max_index);
+
+    /* Use of the output map as a temporary for tracking visited status.  */
+    index_map.truncate (0);
+    index_map.safe_grow_cleared (max_index);
+    for (const basic_block b : blocks)
+	make_index_map_visit (b, L, index_map);
+
+    /* Insert canaries - if there are unreachable nodes (for example infinite
+       loops) then the unreachable nodes should never be needed for comparison,
+       and L.length () < max_index.  An index mapping should also never be
+       recorded twice.  */
+    for (unsigned i = 0; i < index_map.length (); i++)
+	index_map[i] = -1;
+
+    gcc_assert (blocks.length () == L.length ());
+    L.reverse ();
+    const unsigned nblocks = L.length ();
+    for (unsigned i = 0; i < nblocks; i++)
+    {
+	gcc_assert (L[i]->index != -1);
+	index_map[L[i]->index] = int (i);
+    }
+}
+
+/* Walk the CFG and collect conditionals.
+
+   1.  Collect a candidate set G by walking from the root following all
+       (contracted) condition edges.
+   2.  This creates a cut C = (G, G'); find the neighborhood N(G).
+   3.  For every node in N(G), follow the edges across the cut and collect all
+       ancestors (that are also in G).
+   4.  The intersection of all these ancestor sets is the boolean expression B
+       that starts in root.
+
+   Walking is not guaranteed to find nodes in the order of the expression, it
+   might find (a || b) && c as [a c b], so the result must be sorted by the
+   index map.  */
+const vec<basic_block>&
+collect_conditions (conds_ctx& ctx, const basic_block block)
+{
+    vec<basic_block>& blocks = ctx.blocks;
+    blocks.truncate (0);
+
+    if (bitmap_bit_p (ctx.marks, block->index))
+	return blocks;
+
+    if (!block_conditional_p (block))
+    {
+	ctx.mark (block);
+	return blocks;
+    }
+
+    isolate_expression (ctx, block, blocks);
+    ctx.mark (blocks);
+
+    if (blocks.length () > CONDITIONS_MAX_TERMS)
+    {
+	location_t loc = gimple_location (gsi_stmt (gsi_last_bb (block)));
+	warning_at (loc, OPT_Wcoverage_too_many_conditions,
+		    "Too many conditions (found %u); giving up coverage",
+		    blocks.length ());
+	blocks.truncate (0);
+    }
+    return blocks;
+}
+
+/* Used for dfs_enumerate_from () to include all reachable nodes.  */
+bool
+yes (const_basic_block, const void *)
+{
+    return true;
+}
+
+}
+
+struct condcov {
+    explicit condcov (unsigned nblocks) noexcept (true) : ctx (nblocks)
+    {}
+    auto_vec<int, 128> m_index;
+    auto_vec<basic_block, 256> m_blocks;
+    auto_vec<gcov_type_unsigned, 512> m_masks;
+    conds_ctx ctx;
+};
+
+unsigned
+cov_length (const struct condcov* cov)
+{
+    if (cov->m_index.is_empty ())
+	return 0;
+    return cov->m_index.length () - 1;
+}
+
+array_slice<basic_block>
+cov_blocks (struct condcov* cov, unsigned n)
+{
+    if (n >= cov->m_index.length ())
+	return array_slice<basic_block>::invalid ();
+
+    basic_block *begin = cov->m_blocks.begin () + cov->m_index[n];
+    basic_block *end = cov->m_blocks.begin () + cov->m_index[n + 1];
+    return array_slice<basic_block> (begin, end - begin);
+}
+
+array_slice<gcov_type_unsigned>
+cov_masks (struct condcov* cov, unsigned n)
+{
+    if (n >= cov->m_index.length ())
+	return array_slice<gcov_type_unsigned>::invalid ();
+
+    gcov_type_unsigned *begin = cov->m_masks.begin () + 2*cov->m_index[n];
+    gcov_type_unsigned *end = cov->m_masks.begin () + 2*cov->m_index[n + 1];
+    return array_slice<gcov_type_unsigned> (begin, end - begin);
+}
+
+void
+cov_free (struct condcov* cov)
+{
+    delete cov;
+}
+
+/* Condition coverage (MC/DC)
+
+   Algorithm
+   ---------
+   Whalen, Heimdahl, De Silva in "Efficient Test Coverage Measurement for
+   MC/DC" describe an algorithm for modified condition/decision coverage based
+   on AST analysis.  This algorithm analyses the control flow graph to analyze
+   expressions and compute masking vectors, but is inspired by their marking
+   functions for recording outcomes.  The individual phases are described in
+   more detail closer to the implementation.
+
+   The CFG is traversed in DFS order.  It is important that the first basic
+   block in an expression is the first one visited, but the order of
+   independent expressions does not matter.  When the function terminates,
+   every node in the dfs should have been processed and marked exactly once.
+   If there are unreachable nodes they are ignored and not instrumented.
+
+   The CFG is broken up into segments between dominators.  This isn't strictly
+   necessary, but since boolean expressions cannot cross dominators it makes
+   for a nice way to introduce limits to searches.
+
+   The coverage only considers the positions, not the symbols, in a
+   conditional, e.g. !A || (!B && A) is a 3-term conditional even though A
+   appears twice.  Subexpressions have no effect on term ordering:
+   (a && (b || (c && d)) || e) comes out as [a b c d e].
+
+   The output for gcov is a vector of pairs of unsigned integers, interpreted
+   as bit-sets, where the bit index corresponds to the index of the condition
+   in the expression.  */
+struct condcov*
+find_conditions (struct function *fn)
+{
+    record_loop_exits ();
+    mark_dfs_back_edges (fn);
+
+    const bool have_dom = dom_info_available_p (fn, CDI_DOMINATORS);
+    const bool have_post_dom = dom_info_available_p (fn, CDI_POST_DOMINATORS);
+    if (!have_dom)
+	calculate_dominance_info (CDI_DOMINATORS);
+    if (!have_post_dom)
+	calculate_dominance_info (CDI_POST_DOMINATORS);
+
+    const unsigned nblocks = n_basic_blocks_for_fn (fn);
+    condcov *cov = new condcov (nblocks);
+    conds_ctx& ctx = cov->ctx;
+
+    auto_vec<basic_block, 16> dfs;
+    dfs.safe_grow (nblocks);
+    const basic_block entry = ENTRY_BLOCK_PTR_FOR_FN (fn);
+    const basic_block exit = ENTRY_BLOCK_PTR_FOR_FN (fn);
+    int n = dfs_enumerate_from (entry, 0, yes, dfs.address (), nblocks, exit);
+    dfs.truncate (n);
+    make_index_map (dfs, nblocks, ctx.B1, ctx.index_map);
+
+    /* Visit all reachable nodes and collect conditions.  DFS order is
+       important so the first node of a boolean expression is visited first
+       (it will mark subsequent terms).  */
+    cov->m_index.safe_push (0);
+    for (const basic_block b : dfs)
+    {
+	const vec<basic_block>& expr = collect_conditions (ctx, b);
+	if (!expr.is_empty ())
+	{
+	    cov->m_blocks.safe_splice (expr);
+	    cov->m_index.safe_push (cov->m_blocks.length ());
+	}
+    }
+    gcc_assert (ctx.all_marked (dfs));
+
+    if (!have_dom)
+	free_dominance_info (fn, CDI_DOMINATORS);
+    if (!have_post_dom)
+	free_dominance_info (fn, CDI_POST_DOMINATORS);
+
+    cov->m_masks.safe_grow_cleared (2 * cov->m_index.last());
+    const unsigned length = cov_length (cov);
+    for (unsigned i = 0; i < length; i++)
+	masking_vectors (ctx, cov_blocks (cov, i), cov_masks (cov, i));
+
+    return cov;
+}
+
+int
+instrument_decisions (array_slice<basic_block> expr, unsigned condno,
+		      tree *accu, gcov_type_unsigned *masks)
+{
+    /* Zero the local accumulators.  */
+    tree zero = build_int_cst (get_gcov_type (), 0);
+    for (edge e : expr[0]->succs)
+    {
+	gsi_insert_on_edge (e, gimple_build_assign (accu[0], zero));
+	gsi_insert_on_edge (e, gimple_build_assign (accu[1], zero));
+    }
+    /* Add instructions for updating the function-local accumulators.  */
+    for (size_t i = 0; i < expr.size (); i++)
+    {
+	for (edge e : expr[i]->succs)
+	{
+	    if (!edge_conditional_p (e))
+		continue;
+
+	    /* accu |= expr[i] */
+	    const int k = condition_index (e->flags);
+	    tree rhs = build_int_cst (gcov_type_node, 1ULL << i);
+	    emit_bitwise_op (e, accu[k], accu[k], BIT_IOR_EXPR, rhs);
+
+	    if (masks[2*i + k] == 0)
+		continue;
+
+	    /* accu &= mask[i] */
+	    tree mask = build_int_cst (gcov_type_node, ~masks[2*i + k]);
+	    for (int j = 0; j < 2; j++)
+		emit_bitwise_op (e, accu[j], accu[j], BIT_AND_EXPR, mask);
+	}
+    }
+
+    const bool atomic = flag_profile_update == PROFILE_UPDATE_ATOMIC;
+    const tree atomic_ior = builtin_decl_explicit
+	(TYPE_PRECISION (gcov_type_node) > 32
+	 ? BUILT_IN_ATOMIC_FETCH_OR_8
+	 : BUILT_IN_ATOMIC_FETCH_OR_4);
+
+    /* Add instructions for flushing the local accumulators.
+
+       It is important that the flushes happen on on the outcome's incoming
+       edges, otherwise flushes could be lost to exception handling.
+
+       void fn (int a)
+       {
+	   if (a)
+	    fclose ();
+	   exit ();
+       }
+
+       Can yield the CFG:
+       A
+       |\
+       | B
+       |/
+       e
+
+       This typically only happen in optimized builds, but gives linker errors
+       because the counter is left as an undefined symbol.  */
+
+    outcomes out = conditional_succs (expr.back ());
+    const basic_block outcome_blocks[] = { out.t, out.t, out.f, out.f, };
+    const int outcome[] = { 0, 1, 0, 1 };
+    for (int i = 0; i < 4; i++)
+    {
+	const int k = outcome[i];
+	for (edge e : outcome_blocks[i]->preds)
+	{
+	    /* The outcome may have been split and we want to check if the
+	       edge is sourced from inside the expression, so contract it to
+	       find the source conditional edge.  */
+	    e = contract_edge_up (e);
+
+	    /* Only instrument edges from inside the expression.  Sometimes
+	       complicated control flow (like sigsetjmp and gotos) add
+	       predecessors that don't come from the boolean expression.  */
+	    if (index_of (e->src, expr) == -1)
+		continue;
+
+	    tree ref = tree_coverage_counter_ref (GCOV_COUNTER_CONDS,
+						  2*condno + k);
+	    tree tmp = make_temp_ssa_name (gcov_type_node, NULL,
+					   "__conditions_tmp");
+	    if (atomic)
+	    {
+		tree relaxed = build_int_cst (integer_type_node,
+					      MEMMODEL_RELAXED);
+		ref = unshare_expr (ref);
+		gassign *read = gimple_build_assign (tmp, accu[k]);
+		gcall *flush = gimple_build_call (atomic_ior, 3,
+						  build_addr (ref),
+						  gimple_assign_lhs (read),
+						  relaxed);
+
+		gsi_insert_on_edge (e, read);
+		gsi_insert_on_edge (e, flush);
+	    }
+	    else
+	    {
+		gassign *read = gimple_build_assign (tmp, ref);
+		tmp = gimple_assign_lhs (read);
+		gsi_insert_on_edge (e, read);
+		ref = unshare_expr (ref);
+		emit_bitwise_op (e, ref, accu[k], BIT_IOR_EXPR, tmp);
+	    }
+	}
+    }
+    return expr.size ();
+}
+
+#undef CONDITIONS_MAX_TERMS
+#undef EDGE_CONDITION
+
 /* Do initialization work for the edge profiler.  */
 
 /* Add code:
@@ -758,7 +1800,7 @@ tree_profiling (void)
 	  thunk = true;
 	  /* When generate profile, expand thunk to gimple so it can be
 	     instrumented same way as other functions.  */
-	  if (profile_arc_flag)
+	  if (profile_arc_flag || profile_condition_flag)
 	    expand_thunk (node, false, true);
 	  /* Read cgraph profile but keep function as thunk at profile-use
 	     time.  */
@@ -803,7 +1845,7 @@ tree_profiling (void)
   release_profile_file_filtering ();
 
   /* Drop pure/const flags from instrumented functions.  */
-  if (profile_arc_flag || flag_test_coverage)
+  if (profile_arc_flag || profile_condition_flag || flag_test_coverage)
     FOR_EACH_DEFINED_FUNCTION (node)
       {
 	if (!gimple_has_body_p (node->decl)
@@ -897,7 +1939,7 @@ pass_ipa_tree_profile::gate (function *)
      disabled.  */
   return (!in_lto_p && !flag_auto_profile
 	  && (flag_branch_probabilities || flag_test_coverage
-	      || profile_arc_flag));
+	      || profile_arc_flag || profile_condition_flag));
 }
 
 } // anon namespace
diff --git a/libgcc/libgcov-merge.c b/libgcc/libgcov-merge.c
index 89741f637e1..9e3e8ee5657 100644
--- a/libgcc/libgcov-merge.c
+++ b/libgcc/libgcov-merge.c
@@ -33,6 +33,11 @@ void __gcov_merge_add (gcov_type *counters  __attribute__ ((unused)),
                        unsigned n_counters __attribute__ ((unused))) {}
 #endif
 
+#ifdef L_gcov_merge_ior
+void __gcov_merge_ior (gcov_type *counters  __attribute__ ((unused)),
+		       unsigned n_counters __attribute__ ((unused))) {}
+#endif
+
 #ifdef L_gcov_merge_topn
 void __gcov_merge_topn (gcov_type *counters  __attribute__ ((unused)),
 			unsigned n_counters __attribute__ ((unused))) {}
-- 
2.34.0


             reply	other threads:[~2022-12-05  1:41 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-05  1:40 Jørgen Kvalsvik [this message]
2022-12-20  0:31 ` Ping " Jørgen Kvalsvik
2023-03-06  1:47 ` Jørgen Kvalsvik
2023-04-11  6:23 ` Jørgen Kvalsvik
2023-05-15  7:26   ` Ping^ " Jørgen Kvalsvik
2023-05-29  1:04   ` Ping^^ " Jørgen Kvalsvik

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