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* [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple
@ 2021-11-19 1:35 pinskia at gcc dot gnu.org
2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-19 1:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325
Bug ID: 103325
Summary: 1 << -1 is never reduced to a constant during gimple
Product: gcc
Version: 12.0
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: ---
Take:
int main() {
return 1 >> (-1);
}
GCC is the only compiler I have tried (MSVC, ICC and clang/LLVM) which does not
remove the shift.
Yes this is undefined behavior but really I think it is best to reduce to
something rather than keeping around the shift. Even converting it to
__builtin_unreachable will be ok in my book.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple
2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org
@ 2021-11-19 1:36 ` pinskia at gcc dot gnu.org
2021-11-19 7:48 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-19 1:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I should note I noticed this while working on PR 103314.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple
2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org
2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org
@ 2021-11-19 7:48 ` rguenth at gcc dot gnu.org
2021-11-19 12:14 ` pinskia at gcc dot gnu.org
2023-05-28 4:21 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-11-19 7:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-11-19
Ever confirmed|0 |1
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think we used to constant fold this as 1<<1. GCC 7 does
> gcc-7 -S t.c -fdump-tree-original
t.c: In function 'main':
t.c:2:12: warning: right shift count is negative [-Wshift-count-negative]
return 1 >> (-1);
^~
> cat t.c.003t.original
;; Function main (null)
;; enabled by -tree-original
{
return 2;
}
return 0;
but IIRC that behavior was removed from {int_const,wide}_int_binop at some
point, maybe also to enable sanitization.
gimple-ssa-isolate-paths.c would be one place to turn such code into
unreachable or traps (see other PRs to make the behavior configurable).
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple
2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org
2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org
2021-11-19 7:48 ` rguenth at gcc dot gnu.org
@ 2021-11-19 12:14 ` pinskia at gcc dot gnu.org
2023-05-28 4:21 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-19 12:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=96929
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #2)
> but IIRC that behavior was removed from {int_const,wide}_int_binop at some
> point, maybe also to enable sanitization.
This was only done in GCC 11 by r11-5271-g4866b2f5db117f9 (PR96929).
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple
2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org
` (2 preceding siblings ...)
2021-11-19 12:14 ` pinskia at gcc dot gnu.org
@ 2023-05-28 4:21 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-05-28 4:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Target Milestone|--- |12.3
Status|NEW |RESOLVED
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed for GCC 12.3.0 by r12-9091-g9dccaeaa586a16 (aka PR 108306 ). So closing
as fixed.
Note DOM and VRP both do it so it is done at -O1 and -O2.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-05-28 4:21 UTC | newest]
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2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org
2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org
2021-11-19 7:48 ` rguenth at gcc dot gnu.org
2021-11-19 12:14 ` pinskia at gcc dot gnu.org
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