public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors
@ 2024-04-12 14:32 xxs_chy at outlook dot com
2024-04-12 22:34 ` [Bug tree-optimization/114704] " pinskia at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: xxs_chy at outlook dot com @ 2024-04-12 14:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
Bug ID: 114704
Summary: Missed optimization : eliminate store if the value is
known in all predecessors
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: xxs_chy at outlook dot com
Target Milestone: ---
Godbolt link: https://godbolt.org/z/KEeGTM49E
For code like:
```
void src(int *p){
if(*p == 0)
goto then;
else {
dummy();
if(*p == 0)
goto then;
else
return;
}
then:
*p = 0; // *p is already 0, it's dead now
}
```
In then basic block, *p is known to be 0 in all predecessors, thus the store
"*p = 0" is redundant.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/114704] Missed optimization : eliminate store if the value is known in all predecessors
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
@ 2024-04-12 22:34 ` pinskia at gcc dot gnu.org
2024-04-12 22:39 ` pinskia at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-12 22:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Keywords| |missed-optimization
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/114704] Missed optimization : eliminate store if the value is known in all predecessors
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
2024-04-12 22:34 ` [Bug tree-optimization/114704] " pinskia at gcc dot gnu.org
@ 2024-04-12 22:39 ` pinskia at gcc dot gnu.org
2024-04-12 22:41 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-12 22:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
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> ---
Confirmed. A more general testcase:
```
void dummy();
void src(int *p, int a){
int t = *p;
if(t == a)
goto then;
else {
dummy();
t = *p;
if(t == a)
goto then;
else
return;
}
then:
*p = t; // *p is already a, it's dead now
}
```
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/114704] Missed optimization : eliminate store if the value is known in all predecessors
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
2024-04-12 22:34 ` [Bug tree-optimization/114704] " pinskia at gcc dot gnu.org
2024-04-12 22:39 ` pinskia at gcc dot gnu.org
@ 2024-04-12 22:41 ` pinskia at gcc dot gnu.org
2024-04-13 13:39 ` xxs_chy at outlook dot com
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-12 22:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=20999
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Related to PR 20999.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/114704] Missed optimization : eliminate store if the value is known in all predecessors
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
` (2 preceding siblings ...)
2024-04-12 22:41 ` pinskia at gcc dot gnu.org
@ 2024-04-13 13:39 ` xxs_chy at outlook dot com
2024-04-13 18:20 ` pinskia at gcc dot gnu.org
2024-04-15 7:59 ` rguenth at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: xxs_chy at outlook dot com @ 2024-04-13 13:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
--- Comment #3 from XChy <xxs_chy at outlook dot com> ---
(In reply to Andrew Pinski from comment #1)
> Confirmed. A more general testcase:
> ```
> void dummy();
>
> void src(int *p, int a){
> int t = *p;
> if(t == a)
> goto then;
> else {
> dummy();
> t = *p;
> if(t == a)
> goto then;
> else
> return;
> }
>
> then:
> *p = t; // *p is already a, it's dead now
> }
>
> ```
Do you mean "*p = a" at the end?
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/114704] Missed optimization : eliminate store if the value is known in all predecessors
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
` (3 preceding siblings ...)
2024-04-13 13:39 ` xxs_chy at outlook dot com
@ 2024-04-13 18:20 ` pinskia at gcc dot gnu.org
2024-04-15 7:59 ` rguenth at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-13 18:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to XChy from comment #3)
> Do you mean "*p = a" at the end?
In this case a and t should be the same value :). So it does not matter. I was
showing that sometimes gcc messes up when using the original value.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/114704] Missed optimization : eliminate store if the value is known in all predecessors
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
` (4 preceding siblings ...)
2024-04-13 18:20 ` pinskia at gcc dot gnu.org
@ 2024-04-15 7:59 ` rguenth at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-04-15 7:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114704
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
We're not handling "phi translation" in the lookup phase when determining if
there's a redundant store (PHI translation for the virtual operand). In
particular value-numbering never considers whether an expression
in multiple paths into a CFG merge value-numbers the same. This is only
done as part of PRE which figures some extra fully redundant expressions.
But the redundant store removal is something done after-the-fact using
just the VN machinery.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-04-15 7:59 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-04-12 14:32 [Bug tree-optimization/114704] New: Missed optimization : eliminate store if the value is known in all predecessors xxs_chy at outlook dot com
2024-04-12 22:34 ` [Bug tree-optimization/114704] " pinskia at gcc dot gnu.org
2024-04-12 22:39 ` pinskia at gcc dot gnu.org
2024-04-12 22:41 ` pinskia at gcc dot gnu.org
2024-04-13 13:39 ` xxs_chy at outlook dot com
2024-04-13 18:20 ` pinskia at gcc dot gnu.org
2024-04-15 7:59 ` rguenth at gcc dot gnu.org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).