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* [Bug ipa/114703] New: Missed devirtualization in rather simple case
@ 2024-04-12 13:57 konstantin.vladimirov at gmail dot com
2024-04-12 22:01 ` [Bug ipa/114703] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: konstantin.vladimirov at gmail dot com @ 2024-04-12 13:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114703
Bug ID: 114703
Summary: Missed devirtualization in rather simple case
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: konstantin.vladimirov at gmail dot com
Target Milestone: ---
See code here:
https://godbolt.org/z/T9Ma7qe3E
struct A {
virtual int foo() { return 1; }
};
struct B : A {
int foo() override { return 2; }
virtual int foo(int i) { return i + 1; }
};
int use(int, int, int);
int main() {
B *p = new B;
#if 0
A* q = p;
#else
A* q = new B;
#endif
int result1 = p->foo(1);
int result2 = p->foo();
int result3 = q->foo();
use(result1, result2, result3);
}
clang devirtualizes just fine, gcc lacks this one.
Interesting that if you flip preprocessor switch, everything works with gcc
either.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug ipa/114703] Missed devirtualization in rather simple case
2024-04-12 13:57 [Bug ipa/114703] New: Missed devirtualization in rather simple case konstantin.vladimirov at gmail dot com
@ 2024-04-12 22:01 ` pinskia at gcc dot gnu.org
2024-04-12 22:11 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-12 22:01 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114703
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2024-04-12
Status|UNCONFIRMED |NEW
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The problem I think is we don't realize that `operator new` can't touch the
other memory that was just allocated partly because the escape analysis is not
flow sensitive .
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug ipa/114703] Missed devirtualization in rather simple case
2024-04-12 13:57 [Bug ipa/114703] New: Missed devirtualization in rather simple case konstantin.vladimirov at gmail dot com
2024-04-12 22:01 ` [Bug ipa/114703] " pinskia at gcc dot gnu.org
@ 2024-04-12 22:11 ` pinskia at gcc dot gnu.org
2024-04-15 7:53 ` rguenth at gcc dot gnu.org
2024-04-15 10:20 ` hubicka at ucw dot cz
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-12 22:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114703
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug ipa/114703] Missed devirtualization in rather simple case
2024-04-12 13:57 [Bug ipa/114703] New: Missed devirtualization in rather simple case konstantin.vladimirov at gmail dot com
2024-04-12 22:01 ` [Bug ipa/114703] " pinskia at gcc dot gnu.org
2024-04-12 22:11 ` pinskia at gcc dot gnu.org
@ 2024-04-15 7:53 ` rguenth at gcc dot gnu.org
2024-04-15 10:20 ` hubicka at ucw dot cz
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-04-15 7:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114703
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |hubicka at gcc dot gnu.org
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Yep, 'new' memory escapes.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug ipa/114703] Missed devirtualization in rather simple case
2024-04-12 13:57 [Bug ipa/114703] New: Missed devirtualization in rather simple case konstantin.vladimirov at gmail dot com
` (2 preceding siblings ...)
2024-04-15 7:53 ` rguenth at gcc dot gnu.org
@ 2024-04-15 10:20 ` hubicka at ucw dot cz
3 siblings, 0 replies; 5+ messages in thread
From: hubicka at ucw dot cz @ 2024-04-15 10:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114703
--- Comment #3 from Jan Hubicka <hubicka at ucw dot cz> ---
> Yep, 'new' memory escapes.
Yep, this is blocking a lot of propagation in common C++ code.
Here it may help to do speculative devirtualization during IPA stage
that will let the late optimization to get rid of the speculation (since
after inlning we will know that the virtual call does not overwrite
virtual table pointer). This is technically not too hard to add. We
can optimistically rule out (some) may aliases while walking the alias
oracle. I will take a look next stage1.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-04-15 10:20 UTC | newest]
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2024-04-12 13:57 [Bug ipa/114703] New: Missed devirtualization in rather simple case konstantin.vladimirov at gmail dot com
2024-04-12 22:01 ` [Bug ipa/114703] " pinskia at gcc dot gnu.org
2024-04-12 22:11 ` pinskia at gcc dot gnu.org
2024-04-15 7:53 ` rguenth at gcc dot gnu.org
2024-04-15 10:20 ` hubicka at ucw dot cz
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