From: Sergei Trofimovich <[email protected]>
r14-3459-g0c78240fd7d519 "Check that passes do not forget to define profile"
exposed check failures in cases when gcc produces uninitialized profile
probabilities. In case of PR/111559 uninitialized profile is generated
by edges executed 0 times during profile:
__attribute__((noipa)) static void edge(void) {}
int p = 0;
__attribute__((noinline))
static void rule1(void) { if (p) edge(); }
__attribute__((noinline))
static void rule1_same(void) { if (p) edge(); }
__attribute__((noipa)) int main(void) {
rule1();
rule1_same();
}
$ gcc -O2 -fprofile-generate bug.c -o b -fopt-info
$ ./b
$ gcc -O2 -fprofile-use -fprofile-correction bug.c -o b -fopt-info
bug.c: In function 'rule1':
bug.c:6:13: error: probability of edge 3->4 not initialized
6 | static void rule1(void) { if (p) edge(); }
| ^~~~~
during GIMPLE pass: fixup_cfg
bug.c:6:13: internal compiler error: verify_flow_info failed
The change conservatively ignores updates with uninitialized values and
uses initially assigned probabilities (`always` probability in case of
the example).
gcc/
PR/111283
PR/111559
* ipa-utils.cc (ipa_merge_profiles): Avoid producing
uninitialized probabilities when merging counters with zero
denominators.
---
gcc/ipa-utils.cc | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/gcc/ipa-utils.cc b/gcc/ipa-utils.cc
index 956c6294fd7..7c53ae9dd45 100644
--- a/gcc/ipa-utils.cc
+++ b/gcc/ipa-utils.cc
@@ -651,13 +651,17 @@ ipa_merge_profiles (struct cgraph_node *dst,
{
edge srce = EDGE_SUCC (srcbb, i);
edge dste = EDGE_SUCC (dstbb, i);
- dste->probability =
+ profile_probability merged =
dste->probability * dstbb->count.ipa ().probability_in
(dstbb->count.ipa ()
+ srccount.ipa ())
+ srce->probability * srcbb->count.ipa ().probability_in
(dstbb->count.ipa ()
+ srccount.ipa ());
+ /* We produce uninitialized probabilities when
+ denominator is zero: https://gcc.gnu.org/PR111559. */
+ if (merged.initialized_p ())
+ dste->probability = merged;
}
dstbb->count = dstbb->count.ipa () + srccount.ipa ();
}
--
2.42.0
