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* [Bug tree-optimization/114502] New: Missed sccp final value with `a = -a`
@ 2024-03-27 21:02 pinskia at gcc dot gnu.org
2024-03-27 21:07 ` [Bug tree-optimization/114502] " pinskia at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-27 21:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114502
Bug ID: 114502
Summary: Missed sccp final value with `a = -a`
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Inspired by PR 114485 and PR 114476. I noticed that SCCP is not figuring out
what happens when just doing negative of the value. These days we do handle
`^&|` so handling unary - should be in a similar way I suspect.
Testcase:
```
[[gnu::noipa]]
unsigned f(unsigned c) {
for (int i = 0; i < 1024; i ++) {
c *= -1;
}
return c;
}
```
Note non-constant loop bounds handling is in a different bug report even.
The above should be optimized to just `return -c;` for -O2; We do optimize it
at -O3 but that is because the complete loop unroller figures out the cost for
the loop is nothing.
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/114502] Missed sccp final value with `a = -a`
2024-03-27 21:02 [Bug tree-optimization/114502] New: Missed sccp final value with `a = -a` pinskia at gcc dot gnu.org
@ 2024-03-27 21:07 ` pinskia at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-27 21:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114502
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=112104
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Non-constant loop bounds is PR 112104.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2024-03-27 21:02 [Bug tree-optimization/114502] New: Missed sccp final value with `a = -a` pinskia at gcc dot gnu.org
2024-03-27 21:07 ` [Bug tree-optimization/114502] " pinskia at gcc dot gnu.org
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