https://gcc.gnu.org/g:1d3e713dda99e2f56393232e69653c413748bf57
commit r16-2639-g1d3e713dda99e2f56393232e69653c413748bf57
Author: Jan Hubicka <j...@suse.cz>
Date: Wed Jul 30 15:05:18 2025 +0200
Fix fasle profile insonsistency error
This patch fixes false incosistent profile error message seen when building
SPEC with
-fprofile-use -fdump-ipa-profile.
The problem is that with dumping tree_esitmate_probability is run in dry run
mode to report success rates of heuristics. It however runs
determine_unlikely_bbs
which ovewrites some counts to profile_count::zero and later value
profiling sees
the mismatch.
In sane profile determine_unlikely_bbs should be almost always no-op since
it
should only drop to 0 things that are known to be unlikely executed. What
happens here is that there is a comdat where profile is lost and we see a
call with non-zero count calling function with zero count and "fix" the
profile
by making the call to have zero count, too.
I also extended unlikely prediates to avoid tampering with predictions when
prediciton is believed to be reliable. This also avoids us from dropping
all
EH regions to 0 count as tested by the testcase.
gcc/ChangeLog:
* predict.cc (unlikely_executed_edge_p): Ignore EDGE_EH if profile
is reliable.
(unlikely_executed_stmt_p): special case builtin_trap/unreachable
and
ignore other heuristics for reliable profiles.
(tree_estimate_probability): Disable unlikely bb detection when
doing dry run
gcc/testsuite/ChangeLog:
* g++.dg/tree-prof/eh1.C: New test.
Diff:
---
gcc/predict.cc | 28 ++++++++++++++++++++++++++--
gcc/testsuite/g++.dg/tree-prof/eh1.C | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 60 insertions(+), 2 deletions(-)
diff --git a/gcc/predict.cc b/gcc/predict.cc
index 872f54d957a5..5639d81d2770 100644
--- a/gcc/predict.cc
+++ b/gcc/predict.cc
@@ -245,7 +245,10 @@ unlikely_executed_edge_p (edge e)
{
return (e->src->count == profile_count::zero ()
|| e->probability == profile_probability::never ())
- || (e->flags & (EDGE_EH | EDGE_FAKE));
+ || (e->flags & EDGE_FAKE)
+ /* If we read profile and know EH edge is executed, trust it.
+ Otherwise we consider EH edges never executed. */
+ || ((e->flags & EDGE_EH) && !e->probability.reliable_p ());
}
/* Return true if edge E of function FUN is probably never executed. */
@@ -830,6 +833,26 @@ unlikely_executed_stmt_p (gimple *stmt)
{
if (!is_gimple_call (stmt))
return false;
+
+ /* Those calls are inserted by optimizers when code is known to be
+ unreachable or undefined. */
+ if (gimple_call_builtin_p (stmt, BUILT_IN_UNREACHABLE)
+ || gimple_call_builtin_p (stmt, BUILT_IN_UNREACHABLE_TRAP)
+ || gimple_call_builtin_p (stmt, BUILT_IN_TRAP))
+ return false;
+
+ /* Checks below do not need to be fully reliable. Cold attribute may be
+ misplaced by user and in the presence of comdat we may result in call to
+ function with 0 profile having non-zero profile.
+
+ We later detect that profile is lost and will drop the profile of the
+ comdat.
+
+ So if we think profile count is reliable, do not try to apply these
+ heuristics. */
+ if (gimple_bb (stmt)->count.reliable_p ()
+ && gimple_bb (stmt)->count.nonzero_p ())
+ return gimple_bb (stmt)->count == profile_count::zero ();
/* NORETURN attribute alone is not strong enough: exit() may be quite
likely executed once during program run. */
if (gimple_call_fntype (stmt)
@@ -3269,7 +3292,8 @@ tree_estimate_probability (bool dry_run)
calculate_dominance_info (CDI_POST_DOMINATORS);
/* Decide which edges are known to be unlikely. This improves later
branch prediction. */
- determine_unlikely_bbs ();
+ if (!dry_run)
+ determine_unlikely_bbs ();
bb_predictions = new hash_map<const_basic_block, edge_prediction *>;
ssa_expected_value = new hash_map<int_hash<unsigned, 0>, expected_value>;
diff --git a/gcc/testsuite/g++.dg/tree-prof/eh1.C
b/gcc/testsuite/g++.dg/tree-prof/eh1.C
new file mode 100644
index 000000000000..10a35968dc43
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-prof/eh1.C
@@ -0,0 +1,34 @@
+/* { dg-options "-O3 -fdump-ipa-profile-details -fno-inline
-fdump-tree-fixup_cfg3-details -fdump-tree-optimized-details" } */
+char a[10000];
+char b[10000];
+int sz = 1000;
+
+__attribute__((noipa))
+ void test2 ()
+{
+ throw (sz);
+}
+void
+test ()
+{
+ try
+ {
+ test2 ();
+ }
+ catch (int v)
+ {
+ __builtin_memcpy (b, a, v);
+ }
+}
+int
+main ()
+{
+ for (int i = 0; i < 100000; i++)
+ test ();
+}
+/* { dg-final-use-not-autofdo { scan-ipa-dump-times "Average value
sum:100000000" 2 "profile" } } */
+/* 1 zero count for resx block. */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "count: 0" 1 "fixup_cfg3"
} } */
+/* 2 zero count for resx block and return block since return gets duplicated
by tracer. */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "count: 0" 2 "optimized"
} } */
+/* { dg-final-use-not-autofdo { scan-tree-dump-times "Average value
sum:100000000" 1 "optimized" } } */
