[PATCH v3] gcov: Add TARGET_GCOV_TYPE_SIZE target macro

[PATCH v3] gcov: Add TARGET_GCOV_TYPE_SIZE target macro

[Sebastian Huber]

If -fprofile-update=atomic is used, then the target must provide atomic
operations for the counters of the type returned by get_gcov_type().
This is a 64-bit type for targets which have a 64-bit long long type.
On 32-bit targets this could be an issue since they may not provide
64-bit atomic operations.  Allow targets to override the default type
size with the new TARGET_GCOV_TYPE_SIZE target macro.

If a 32-bit gcov type size is used, then there is currently a warning in
libgcov-driver.c in a dead code block due to
sizeof (counter) == sizeof (gcov_unsigned_t):

libgcc/libgcov-driver.c: In function 'dump_counter':
libgcc/libgcov-driver.c:401:46: warning: right shift count >= width of type [-Wshift-count-overflow]
  401 |     dump_unsigned ((gcov_unsigned_t)(counter >> 32), dump_fn, arg);
      |                                              ^~

gcc/

	* c-family/c-cppbuiltin.c (c_cpp_builtins): Define
	__LIBGCC_GCOV_TYPE_SIZE if flag_building_libgcc is true.
	* config/sparc/rtemself.h (TARGET_GCOV_TYPE_SIZE): Redefine.
	* coverage.c (get_gcov_type): Use targetm.gcov_type_size.
	* doc/tm.texi (TARGET_GCOV_TYPE_SIZE): Add hook under "Misc".
	* doc/tm.texi.in: Regenerate.
	* target.def (gcov_type_size): New POD hook.
	* tree-profile.c (gimple_gen_edge_profiler): Use precision of
	gcov_type_node.
	(gimple_gen_time_profiler): Likewise.

libgcc/

	* libgcov.h (gcov_type): Define using __LIBGCC_GCOV_TYPE_SIZE.
	(gcov_type_unsigned): Likewise.
---
 gcc/c-family/c-cppbuiltin.c |  2 ++
 gcc/config/sparc/rtemself.h |  3 +++
 gcc/coverage.c              |  3 +--
 gcc/doc/tm.texi             | 11 +++++++++++
 gcc/doc/tm.texi.in          |  2 ++
 gcc/target.def              | 12 ++++++++++++
 gcc/tree-profile.c          |  4 ++--
 libgcc/libgcov.h            |  6 +++---
 8 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/gcc/c-family/c-cppbuiltin.c b/gcc/c-family/c-cppbuiltin.c
index f79f939bd10f..e85b60c79f49 100644
--- a/gcc/c-family/c-cppbuiltin.c
+++ b/gcc/c-family/c-cppbuiltin.c
@@ -1450,6 +1450,8 @@ c_cpp_builtins (cpp_reader *pfile)
       /* For libgcov.  */
       builtin_define_with_int_value ("__LIBGCC_VTABLE_USES_DESCRIPTORS__",
 				     TARGET_VTABLE_USES_DESCRIPTORS);
+      builtin_define_with_int_value ("__LIBGCC_GCOV_TYPE_SIZE",
+				     TARGET_GCOV_TYPE_SIZE);
     }
 
   /* For use in assembly language.  */
diff --git a/gcc/config/sparc/rtemself.h b/gcc/config/sparc/rtemself.h
index fa972af640cc..87a3ceb640c0 100644
--- a/gcc/config/sparc/rtemself.h
+++ b/gcc/config/sparc/rtemself.h
@@ -40,3 +40,6 @@
 
 /* Use the default */
 #undef LINK_GCC_C_SEQUENCE_SPEC
+
+#undef TARGET_GCOV_TYPE_SIZE
+#define TARGET_GCOV_TYPE_SIZE 32
diff --git a/gcc/coverage.c b/gcc/coverage.c
index ac9a9fdad228..6166247ad179 100644
--- a/gcc/coverage.c
+++ b/gcc/coverage.c
@@ -145,8 +145,7 @@ static void coverage_obj_finish (vec<constructor_elt, va_gc> *);
 tree
 get_gcov_type (void)
 {
-  scalar_int_mode mode
-    = smallest_int_mode_for_size (LONG_LONG_TYPE_SIZE > 32 ? 64 : 32);
+  scalar_int_mode mode = smallest_int_mode_for_size (targetm.gcov_type_size);
   return lang_hooks.types.type_for_mode (mode, false);
 }
 
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index a30fdcbbf3d6..429e7edf0e9d 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -12588,3 +12588,14 @@ Return an RTX representing @var{tagged_pointer} with its tag set to zero.
 Store the result in @var{target} if convenient.
 The default clears the top byte of the original pointer.
 @end deftypefn
+
+@deftypevr {Target Hook} HOST_WIDE_INT TARGET_GCOV_TYPE_SIZE
+The gcov type size in bits.  This type is used for example for counters
+incremented by profiling and code-coverage events.  The default value is 64,
+if the type size of long long is greater than 32, otherwise the default
+value is 32.  A 64-bit type is recommended to avoid overflows of the
+counters.  If the @option{-fprofile-update=atomic} is used, then the
+counters are incremented using atomic operations.  Targets not supporting
+64-bit atomic operations may override the default value and request a 32-bit
+type.
+@end deftypevr
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 611fc500ac86..fdf16b901c53 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -8180,3 +8180,5 @@ maintainer is familiar with.
 @hook TARGET_MEMTAG_EXTRACT_TAG
 
 @hook TARGET_MEMTAG_UNTAGGED_POINTER
+
+@hook TARGET_GCOV_TYPE_SIZE
diff --git a/gcc/target.def b/gcc/target.def
index 7676d5e626e3..b94c2c40dcf1 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -7104,6 +7104,18 @@ DEFHOOK
  void, (void),
  NULL)
 
+DEFHOOKPOD
+(gcov_type_size,
+ "The gcov type size in bits.  This type is used for example for counters\n\
+incremented by profiling and code-coverage events.  The default value is 64,\n\
+if the type size of long long is greater than 32, otherwise the default\n\
+value is 32.  A 64-bit type is recommended to avoid overflows of the\n\
+counters.  If the @option{-fprofile-update=atomic} is used, then the\n\
+counters are incremented using atomic operations.  Targets not supporting\n\
+64-bit atomic operations may override the default value and request a 32-bit\n\
+type.",
+ HOST_WIDE_INT, (LONG_LONG_TYPE_SIZE > 32 ? 64 : 32))
+
 /* Close the 'struct gcc_target' definition.  */
 HOOK_VECTOR_END (C90_EMPTY_HACK)
 
diff --git a/gcc/tree-profile.c b/gcc/tree-profile.c
index 5a74cc96e132..cf46912631cb 100644
--- a/gcc/tree-profile.c
+++ b/gcc/tree-profile.c
@@ -250,7 +250,7 @@ gimple_gen_edge_profiler (int edgeno, edge e)
     {
       /* __atomic_fetch_add (&counter, 1, MEMMODEL_RELAXED); */
       tree addr = tree_coverage_counter_addr (GCOV_COUNTER_ARCS, edgeno);
-      tree f = builtin_decl_explicit (LONG_LONG_TYPE_SIZE > 32
+      tree f = builtin_decl_explicit (TYPE_PRECISION (gcov_type_node) > 32
 				      ? BUILT_IN_ATOMIC_FETCH_ADD_8:
 				      BUILT_IN_ATOMIC_FETCH_ADD_4);
       gcall *stmt = gimple_build_call (f, 3, addr, one,
@@ -525,7 +525,7 @@ gimple_gen_time_profiler (unsigned tag)
 			  tree_time_profiler_counter);
       gassign *assign = gimple_build_assign (ptr, NOP_EXPR, addr);
       gsi_insert_before (&gsi, assign, GSI_NEW_STMT);
-      tree f = builtin_decl_explicit (LONG_LONG_TYPE_SIZE > 32
+      tree f = builtin_decl_explicit (TYPE_PRECISION (gcov_type_node) > 32
 				      ? BUILT_IN_ATOMIC_ADD_FETCH_8:
 				      BUILT_IN_ATOMIC_ADD_FETCH_4);
       gcall *stmt = gimple_build_call (f, 3, ptr, one,
diff --git a/libgcc/libgcov.h b/libgcc/libgcov.h
index 9c537253293f..f6354a7a0705 100644
--- a/libgcc/libgcov.h
+++ b/libgcc/libgcov.h
@@ -52,7 +52,7 @@
 #if __CHAR_BIT__ == 8
 typedef unsigned gcov_unsigned_t __attribute__ ((mode (SI)));
 typedef unsigned gcov_position_t __attribute__ ((mode (SI)));
-#if LONG_LONG_TYPE_SIZE > 32
+#if __LIBGCC_GCOV_TYPE_SIZE > 32
 typedef signed gcov_type __attribute__ ((mode (DI)));
 typedef unsigned gcov_type_unsigned __attribute__ ((mode (DI)));
 #else
@@ -63,7 +63,7 @@ typedef unsigned gcov_type_unsigned __attribute__ ((mode (SI)));
 #if __CHAR_BIT__ == 16
 typedef unsigned gcov_unsigned_t __attribute__ ((mode (HI)));
 typedef unsigned gcov_position_t __attribute__ ((mode (HI)));
-#if LONG_LONG_TYPE_SIZE > 32
+#if __LIBGCC_GCOV_TYPE_SIZE > 32
 typedef signed gcov_type __attribute__ ((mode (SI)));
 typedef unsigned gcov_type_unsigned __attribute__ ((mode (SI)));
 #else
@@ -73,7 +73,7 @@ typedef unsigned gcov_type_unsigned __attribute__ ((mode (HI)));
 #else
 typedef unsigned gcov_unsigned_t __attribute__ ((mode (QI)));
 typedef unsigned gcov_position_t __attribute__ ((mode (QI)));
-#if LONG_LONG_TYPE_SIZE > 32
+#if __LIBGCC_GCOV_TYPE_SIZE > 32
 typedef signed gcov_type __attribute__ ((mode (HI)));
 typedef unsigned gcov_type_unsigned __attribute__ ((mode (HI)));
 #else
-- 
2.26.2

Re: [PATCH v3] gcov: Add TARGET_GCOV_TYPE_SIZE target macro

[Joseph Myers]

On Wed, 11 Aug 2021, Sebastian Huber wrote:

> 64-bit atomic operations.  Allow targets to override the default type
> size with the new TARGET_GCOV_TYPE_SIZE target macro.

Hook, not macro.

> diff --git a/gcc/c-family/c-cppbuiltin.c b/gcc/c-family/c-cppbuiltin.c
> index f79f939bd10f..e85b60c79f49 100644
> --- a/gcc/c-family/c-cppbuiltin.c
> +++ b/gcc/c-family/c-cppbuiltin.c
> @@ -1450,6 +1450,8 @@ c_cpp_builtins (cpp_reader *pfile)
>        /* For libgcov.  */
>        builtin_define_with_int_value ("__LIBGCC_VTABLE_USES_DESCRIPTORS__",
>  				     TARGET_VTABLE_USES_DESCRIPTORS);
> +      builtin_define_with_int_value ("__LIBGCC_GCOV_TYPE_SIZE",
> +				     TARGET_GCOV_TYPE_SIZE);

The TARGET_* macros used to initialize targetm may only be defined to 
their final values in the architecture-specific .c file that actually 
defines targetm.  All other files should access the hook via targetm, not 
the TARGET_* macros.  (TARGET_VTABLE_USES_DESCRIPTORS in the diff context 
is a target macro, not a hook at all.)

> +DEFHOOKPOD
> +(gcov_type_size,
> + "The gcov type size in bits.  This type is used for example for counters\n\
> +incremented by profiling and code-coverage events.  The default value is 64,\n\
> +if the type size of long long is greater than 32, otherwise the default\n\
> +value is 32.  A 64-bit type is recommended to avoid overflows of the\n\
> +counters.  If the @option{-fprofile-update=atomic} is used, then the\n\
> +counters are incremented using atomic operations.  Targets not supporting\n\
> +64-bit atomic operations may override the default value and request a 32-bit\n\
> +type.",
> + HOST_WIDE_INT, (LONG_LONG_TYPE_SIZE > 32 ? 64 : 32))

LONG_LONG_TYPE_SIZE may depend on command-line options passed to the 
compiler (it does for AVR).  The hook thus needs to be a function 
returning the desired size.

-- 
Joseph S. Myers
joseph@codesourcery.com