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* [Bug tree-optimization/114737] New: Missed optimization : fail to optimize load with select clobber
@ 2024-04-16 7:55 xxs_chy at outlook dot com
2024-04-16 10:47 ` [Bug tree-optimization/114737] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: xxs_chy at outlook dot com @ 2024-04-16 7:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114737
Bug ID: 114737
Summary: Missed optimization : fail to optimize load with
select clobber
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/3e5sfvfKj
```
char src(void** p, char* p1, bool c) {
char* tostore1 = p1 + 1;
char* tostore2 = p1 + 4;
*p = tostore1;
*p1 = 0;
char* tostore = (c ? tostore1 : tostore2) + 1;
*tostore = 1;
return *p1;
}
```
"return *p1" can be optimized into "return 0" here.
```
char tgt(void** p, char* p1, bool c) {
char* tostore1 = p1 + 1;
char* tostore2 = p1 + 4;
*p = tostore1;
*p1 = 0;
char* tostore = (c ? tostore1 : tostore2) + 1;
*tostore = 1;
return 0;
}
```
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/114737] Missed optimization : fail to optimize load with select clobber
2024-04-16 7:55 [Bug tree-optimization/114737] New: Missed optimization : fail to optimize load with select clobber xxs_chy at outlook dot com
@ 2024-04-16 10:47 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-04-16 10:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114737
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2024-04-16
Status|UNCONFIRMED |NEW
Keywords| |alias, missed-optimization
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. points-to analysis does not track pointer offsets for the final
points-to sets, so tostore and p1 point to the same object. Specifically
pointer offset gathering when setting up the ao_ref for *to_store_1
doesn't look through PHIs:
<bb 3> :
# PT = nonlocal null
tostore_11 = p1_2(D) + 2;
goto <bb 5>; [INV]
<bb 4> :
# PT = nonlocal null
tostore_10 = p1_2(D) + 5;
<bb 5> :
# PT = nonlocal null
# tostore_1 = PHI <tostore_11(3), tostore_10(4)>
*tostore_1 = 1;
what in this case would help a little bit is if this were
<bb 3> :
goto <bb 5>; [INV]
<bb 4> :
<bb 5> :
# PT = nonlocal null
# offset_3 = PHI <2(3), 5(4)>
# PT = nonlocal null
tostore_1 = p1_2(D) + offset_3;
*tostore_1 = 1;
then eventually range-info for offset_3 could be used to constrain the
ao_ref.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2024-04-16 7:55 [Bug tree-optimization/114737] New: Missed optimization : fail to optimize load with select clobber xxs_chy at outlook dot com
2024-04-16 10:47 ` [Bug tree-optimization/114737] " rguenth at gcc dot gnu.org
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