[PATCH] Introduce -fprofile-update=maybe-atomic

["Martin Liška" <mliska@suse.cz>]

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Hello.

As it's very hard to guess from GCC driver whether a target supports atomic updates
for GCOV counter or not, I decided to come up with a new option value (maybe-atomic),
that would be transformed in a corresponding value (single or atomic) in tree-profile.c.
The GCC driver selects the option when -pthread is present in the command line.

That should fix all tests failures seen on AIX target.

Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.

Ready to be installed?
Martin

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From 1d00b7b4d42d080fe4d6cd51a03829b0fe525c9d Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Wed, 12 Oct 2016 15:05:49 +0200
Subject: [PATCH] Introduce -fprofile-update=maybe-atomic

gcc/ChangeLog:

2016-10-12  Martin Liska  <mliska@suse.cz>

	* common.opt: Add maybe-atomic as a new enum value for
	-fprofile-update.
	* coretypes.h: Likewise.
	* doc/invoke.texi: Document the new option value.
	* gcc.c: Replace atomic with maybe-atomic.  Remove warning.
	* tree-profile.c (tree_profiling): Select default value
	of -fprofile-update when 'maybe-atomic' is selected.

gcc/testsuite/ChangeLog:

2016-10-12  Martin Liska  <mliska@suse.cz>

	* gcc.dg/no_profile_instrument_function-attr-1.c: Update test
	to match scanned pattern.
	* gcc.dg/tree-ssa/ssa-lim-11.c: Likewise.
---
 gcc/common.opt                                     |  5 +++-
 gcc/coretypes.h                                    |  3 +-
 gcc/doc/invoke.texi                                | 11 +++++--
 gcc/gcc.c                                          |  6 +---
 .../gcc.dg/no_profile_instrument_function-attr-1.c |  2 +-
 gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-11.c         |  2 +-
 gcc/tree-profile.c                                 | 35 +++++++++++-----------
 7 files changed, 35 insertions(+), 29 deletions(-)

diff --git a/gcc/common.opt b/gcc/common.opt
index 15679c5..d6c5acd 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1937,7 +1937,7 @@ Enable correction of flow inconsistent profile data input.
 
 fprofile-update=
 Common Joined RejectNegative Enum(profile_update) Var(flag_profile_update) Init(PROFILE_UPDATE_SINGLE)
--fprofile-update=[single|atomic]	Set the profile update method.
+-fprofile-update=[single|atomic|maybe-atomic]	Set the profile update method.
 
 Enum
 Name(profile_update) Type(enum profile_update) UnknownError(unknown profile update method %qs)
@@ -1948,6 +1948,9 @@ Enum(profile_update) String(single) Value(PROFILE_UPDATE_SINGLE)
 EnumValue
 Enum(profile_update) String(atomic) Value(PROFILE_UPDATE_ATOMIC)
 
+EnumValue
+Enum(profile_update) String(maybe-atomic) Value(PROFILE_UPDATE_MAYBE_ATOMIC)
+
 fprofile-generate
 Common
 Enable common options for generating profile info for profile feedback directed optimizations.
diff --git a/gcc/coretypes.h b/gcc/coretypes.h
index fe1e984..aec2a6e 100644
--- a/gcc/coretypes.h
+++ b/gcc/coretypes.h
@@ -177,7 +177,8 @@ enum offload_abi {
 /* Types of profile update methods.  */
 enum profile_update {
   PROFILE_UPDATE_SINGLE,
-  PROFILE_UPDATE_ATOMIC
+  PROFILE_UPDATE_ATOMIC,
+  PROFILE_UPDATE_MAYBE_ATOMIC
 };
 
 /* Types of unwind/exception handling info that can be generated.  */
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c11f1d5..eb6cae3 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -10315,13 +10315,18 @@ To optimize the program based on the collected profile information, use
 
 Alter the update method for an application instrumented for profile
 feedback based optimization.  The @var{method} argument should be one of
-@samp{single} or @samp{atomic}.  The first one is useful for single-threaded
-applications, while the second one prevents profile corruption by emitting
-thread-safe code.
+@samp{single}, @samp{atomic} or @samp{maybe-atomic}.
+The first one is useful for single-threaded applications,
+while the second one prevents profile corruption by emitting thread-safe code.
 
 @strong{Warning:} When an application does not properly join all threads
 (or creates an detached thread), a profile file can be still corrupted.
 
+Using @samp{maybe-atomic} would be transformed either to @samp{atomic},
+when supported by a target, or to @samp{single} otherwise. The GCC driver
+automatically selects @samp{maybe-atomic} when @option{-pthread}
+is present in the command line.
+
 @item -fsanitize=address
 @opindex fsanitize=address
 Enable AddressSanitizer, a fast memory error detector.
diff --git a/gcc/gcc.c b/gcc/gcc.c
index 5213cb0..1959fc7 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -1144,11 +1144,7 @@ static const char *cc1_options =
  %{coverage:-fprofile-arcs -ftest-coverage}\
  %{fprofile-arcs|fprofile-generate*|coverage:\
    %{!fprofile-update=single:\
-     %{pthread:-fprofile-update=atomic}}}\
- %{fprofile-update=single:\
-   %{fprofile-arcs|fprofile-generate*|coverage:\
-     %{pthread:%n-fprofile-update=atomic should be used\
- for a multithreaded application}}}";
+     %{pthread:-fprofile-update=maybe-atomic}}}";
 
 static const char *asm_options =
 "%{-target-help:%:print-asm-header()} "
diff --git a/gcc/testsuite/gcc.dg/no_profile_instrument_function-attr-1.c b/gcc/testsuite/gcc.dg/no_profile_instrument_function-attr-1.c
index c93d171..29bffd90 100644
--- a/gcc/testsuite/gcc.dg/no_profile_instrument_function-attr-1.c
+++ b/gcc/testsuite/gcc.dg/no_profile_instrument_function-attr-1.c
@@ -1,4 +1,4 @@
-/* { dg-options "-O2 -fprofile-generate -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fprofile-generate -fprofile-update=single -fdump-tree-optimized" } */
 
 __attribute__ ((no_profile_instrument_function))
 int foo()
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-11.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-11.c
index e4c11aa..4c38982 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-11.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-11.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fprofile-arcs -fdump-tree-lim2-details" } */
+/* { dg-options "-O -fprofile-arcs -fprofile-update=single -fdump-tree-lim2-details" } */
 /* { dg-require-profiling "-fprofile-generate" } */
 
 struct thread_param
diff --git a/gcc/tree-profile.c b/gcc/tree-profile.c
index 1f45b99..fcef2e5 100644
--- a/gcc/tree-profile.c
+++ b/gcc/tree-profile.c
@@ -534,25 +534,26 @@ tree_profiling (void)
   struct cgraph_node *node;
 
   /* Verify whether we can utilize atomic update operations.  */
-  if (flag_profile_update == PROFILE_UPDATE_ATOMIC)
+  bool can_support_atomic = false;
+  unsigned HOST_WIDE_INT gcov_type_size
+    = tree_to_uhwi (TYPE_SIZE_UNIT (get_gcov_type ()));
+  if (gcov_type_size == 4)
+    can_support_atomic
+      = HAVE_sync_compare_and_swapsi || HAVE_atomic_compare_and_swapsi;
+  else if (gcov_type_size == 8)
+    can_support_atomic
+      = HAVE_sync_compare_and_swapdi || HAVE_atomic_compare_and_swapdi;
+
+  if (flag_profile_update == PROFILE_UPDATE_ATOMIC
+      && !can_support_atomic)
     {
-      bool can_support = false;
-      unsigned HOST_WIDE_INT gcov_type_size
-	= tree_to_uhwi (TYPE_SIZE_UNIT (get_gcov_type ()));
-      if (gcov_type_size == 4)
-	can_support
-	  = HAVE_sync_compare_and_swapsi || HAVE_atomic_compare_and_swapsi;
-      else if (gcov_type_size == 8)
-	can_support
-	  = HAVE_sync_compare_and_swapdi || HAVE_atomic_compare_and_swapdi;
-
-      if (!can_support)
-      {
-	warning (0, "target does not support atomic profile update, "
-		 "single mode is selected");
-	flag_profile_update = PROFILE_UPDATE_SINGLE;
-      }
+      warning (0, "target does not support atomic profile update, "
+	       "single mode is selected");
+      flag_profile_update = PROFILE_UPDATE_SINGLE;
     }
+  else if (flag_profile_update == PROFILE_UPDATE_MAYBE_ATOMIC)
+    flag_profile_update = can_support_atomic
+      ? PROFILE_UPDATE_ATOMIC : PROFILE_UPDATE_SINGLE;
 
   /* This is a small-ipa pass that gets called only once, from
      cgraphunit.c:ipa_passes().  */
-- 
2.9.2