[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559 Sergei Trofimovich changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution|--- |FIXED Assignee|unassigned at gcc dot gnu.org |slyfox at gcc dot gnu.org --- Comment #10 from Sergei Trofimovich --- Fixed in master. Thanks for the report!
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559
--- Comment #9 from CVS Commits ---
The master branch has been updated by Sergei Trofimovich :
https://gcc.gnu.org/g:043a6fcbc27f8721301eb2f72a7839f54f393003
commit r14-4421-g043a6fcbc27f8721301eb2f72a7839f54f393003
Author: Sergei Trofimovich
Date: Wed Sep 27 14:29:12 2023 +0100
ipa-utils: avoid uninitialized probabilities on ICF [PR111559]
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 reported by IPA profile:
$ gcc -O2 -fprofile-generate pr111559.c -o b -fopt-info
$ ./b
$ gcc -O2 -fprofile-use -fprofile-correction pr111559.c -o b -fopt-info
pr111559.c: In function 'rule1':
pr111559.c:6:13: error: probability of edge 3->4 not initialized
6 | static void rule1(void) { if (p) edge(); }
| ^
during GIMPLE pass: fixup_cfg
pr111559.c:6:13: internal compiler error: verify_flow_info failed
The change conservatively ignores updates with zero execution counts and
uses initially assigned probabilities (`always` probability in case of
the example).
PR ipa/111283
PR gcov-profile/111559
gcc/
* ipa-utils.cc (ipa_merge_profiles): Avoid producing
uninitialized probabilities when merging counters with zero
denominators.
gcc/testsuite/
* gcc.dg/tree-prof/pr111559.c: New test.
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559 --- Comment #8 from Franz Sirl --- The proposed patch on top of r14-4307 fixes the profiled bootstrap here.
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559 --- Comment #7 from Sergei Trofimovich --- Proposed conservative fix as https://gcc.gnu.org/pipermail/gcc-patches/2023-September/631526.html
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559
--- Comment #6 from Sergei Trofimovich ---
Uninitialized value comes from `ipa_merge_profiles()` for our `rule1_same()`
alias and `rule1()` functions:
// in gcc/ipa-icf.cc:
else if (create_alias)
{
alias->icf_merged = true;
/* Remove the function's body. */
ipa_merge_profiles (original, alias);
// ...
If I comment out `ipa_merge_profiles (original, alias);` call to leave
`original` as is then failure does not happen. Which means at least
`original`'s profile is fine.
Tracing through `ipa_merge_profiles()` we generate uninitialized probalility
profile when divide by zero at:
// in gcc/ipa-utils.cc
void
ipa_merge_profiles (struct cgraph_node *dst,
struct cgraph_node *src,
bool preserve_body)
// ...
/* TODO: merge also statement histograms. */
FOR_ALL_BB_FN (srcbb, srccfun)
{
unsigned int i;
if (copy_counts) { /* snip: ireelevant */ }
else
{
for (i = 0; i < EDGE_COUNT (srcbb->succs); i++)
{
edge srce = EDGE_SUCC (srcbb, i);
edge dste = EDGE_SUCC (dstbb, i);
dste->probability =
dste->probability * dstbb->count.ipa ().probability_in
(dstbb->count.ipa ()
+ srccount.ipa ())
+ srce->probability * srcbb->count.ipa ().probability_in
(dstbb->count.ipa ()
+ srccount.ipa ());
}
dstbb->count = dstbb->count.ipa () + srccount.ipa ();
}
}
// ...
Here `dstbb->count.ipa () + srccount.ipa ()` is zero.
This assert should expose it as well:
--- a/gcc/ipa-utils.cc
+++ b/gcc/ipa-utils.cc
@@ -651,13 +651,15 @@ ipa_merge_profiles (struct cgraph_node *dst,
{
edge srce = EDGE_SUCC (srcbb, i);
edge dste = EDGE_SUCC (dstbb, i);
+
+ profile_count den = dstbb->count.ipa () + srccount.ipa ();
+ gcc_assert(den.nonzero_p());
+
dste->probability =
dste->probability * dstbb->count.ipa ().probability_in
-(dstbb->count.ipa ()
- + srccount.ipa ())
+(den)
+ srce->probability * srcbb->count.ipa ().probability_in
-(dstbb->count.ipa ()
- + srccount.ipa ());
+(den);
}
dstbb->count = dstbb->count.ipa () + srccount.ipa ();
}
If we attach `gdb` it agrees we exercise these edges 0 times.
(gdb) call dstbb->count.debug()
0 (precise)
(gdb) call srccount.ipa ().debug()
0 (precise)
For comparison we are trying to clobber `always` probability with `undefined`:
(gdb) call dste->probability.debug()
always
What edge is that?
(gdb) call debug_edge(srce)
edge (bb_3, bb_4)
__attribute__((noinline))
void rule1 ()
{
int p.0_1;
[count: 2]:
p.0_1 = p;
if (p.0_1 != 0)
goto ; [0.00%]
else
goto ; [100.00%]
[count: 0]:
edge ();
[count: 2]:
return;
}
`always` should valid for `bb_3->bb_4`. But for our data input it's `never`.
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559
--- Comment #5 from Sergei Trofimovich ---
Slightly shorter example that does not rely on inline:
// $ cat bug.c
__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();
}
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
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559
--- Comment #4 from Sergei Trofimovich ---
Looks like identical code folding creates uninitialized profile counters if
there are any edges in folded functions.
I think cvise did a decent job extracting the reproducer below. Here is a
single-file trigger on `--enable-checking=yes` `gcc` from `master`:
```
// $ cat bug.c
__attribute__((noipa)) static void edge(void) {}
static void rule1(int *p) {
edge();
if (*p) edge();
}
static void rule1_same(int *p) {
edge();
if (*p) edge();
}
__attribute__((noipa)) int main(void) {
int p = 0;
rule1();
rule1_same();
}
```
Trigger:
```
$ echo PG
$ gcc -O2 -fprofile-generate bug.c -o b -fopt-info
$ echo RUN
$ ./b
$ echo PU
$ gcc -O2 -fprofile-use -fprofile-correction bug.c -o b -fopt-info
```
Running:
```
PG
$ gcc -O2 -fprofile-generate bug.c -o b -fopt-info
bug.c:15:5: optimized: Inlined rule1.constprop/28 into main/3 which now has
time 75.28 and size 51, net change of -6.
bug.c:16:5: optimized: Inlined rule1_same.constprop/27 into main/3 which now
has time 94.56 and size 72, net change of -6.
RUN
$ ./b
PU
$ gcc -O2 -fprofile-use -fprofile-correction bug.c -o b -fopt-info
bug.c:3:13: optimized: Semantic equality hit:rule1/1->rule1_same/2
bug.c:3:13: optimized: Assembler symbol names:rule1/1->rule1_same/2
bug.c:15:5: optimized: Inlined rule1.constprop/5 into main/3 which now has
time 26.00 and size 10, net change of +2.
bug.c:16:5: optimized: Inlined rule1.constprop/4 into main/3 which now has
time 27.00 and size 12, net change of -6.
bug.c: In function 'main':
bug.c:13:28: error: probability of edge 3->4 not initialized
13 | __attribute__((noipa)) int main(void) {
|^~~~
bug.c:13:28: error: probability of edge 5->6 not initialized
during IPA pass: inline
bug.c:13:28: internal compiler error: verify_flow_info failed
```
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559 Franz Sirl changed: What|Removed |Added CC||sirl at gcc dot gnu.org --- Comment #3 from Franz Sirl --- Looks like a dup of the profiledbootstrap fail bug 111283
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559 Sergei Trofimovich changed: What|Removed |Added CC||slyfox at gcc dot gnu.org --- Comment #2 from Sergei Trofimovich --- Possibly exposed by r14-3459-g0c78240fd7d519 "Check that passes do not forget to define profile"
[Bug gcov-profile/111559] [14 regression] ICE when building Python with PGO
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111559 Andrew Pinski changed: What|Removed |Added CC||hubicka at gcc dot gnu.org Target Milestone|--- |14.0
