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* [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally
@ 2020-08-19 13:03 gabravier at gmail dot com
2020-08-19 13:08 ` [Bug tree-optimization/96707] " gabravier at gmail dot com
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: gabravier at gmail dot com @ 2020-08-19 13:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
Bug ID: 96707
Summary: Failure to optimize right shift+unsigned compare of
two variables optimally
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
bool f(unsigned x, unsigned y)
{
return (x >> y) <= x;
}
This can be optimized to `return true;`. This transformation is done by LLVM,
but not by GCC.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
@ 2020-08-19 13:08 ` gabravier at gmail dot com
2020-08-24 22:32 ` pinskia at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: gabravier at gmail dot com @ 2020-08-19 13:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
--- Comment #1 from Gabriel Ravier <gabravier at gmail dot com> ---
PS: This transformation can also be done with a very similar pattern where the
return statement is replaced with this : `return (x / y) <= x;`
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
2020-08-19 13:08 ` [Bug tree-optimization/96707] " gabravier at gmail dot com
@ 2020-08-24 22:32 ` pinskia at gcc dot gnu.org
2020-08-25 11:07 ` rguenth at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2020-08-24 22:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
2020-08-19 13:08 ` [Bug tree-optimization/96707] " gabravier at gmail dot com
2020-08-24 22:32 ` pinskia at gcc dot gnu.org
@ 2020-08-25 11:07 ` rguenth at gcc dot gnu.org
2021-01-02 9:14 ` jakub at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-08-25 11:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-08-25
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
` (2 preceding siblings ...)
2020-08-25 11:07 ` rguenth at gcc dot gnu.org
@ 2021-01-02 9:14 ` jakub at gcc dot gnu.org
2021-01-04 15:00 ` amacleod at redhat dot com
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-01-02 9:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |amacleod at redhat dot com,
| |jakub at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think another case for ranger symbolic ranges?
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
` (3 preceding siblings ...)
2021-01-02 9:14 ` jakub at gcc dot gnu.org
@ 2021-01-04 15:00 ` amacleod at redhat dot com
2022-01-12 2:00 ` amacleod at redhat dot com
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: amacleod at redhat dot com @ 2021-01-04 15:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
--- Comment #3 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Jakub Jelinek from comment #2)
> I think another case for ranger symbolic ranges?
indeed.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
` (4 preceding siblings ...)
2021-01-04 15:00 ` amacleod at redhat dot com
@ 2022-01-12 2:00 ` amacleod at redhat dot com
2022-01-13 18:52 ` cvs-commit at gcc dot gnu.org
2022-01-13 18:52 ` amacleod at redhat dot com
7 siblings, 0 replies; 9+ messages in thread
From: amacleod at redhat dot com @ 2022-01-12 2:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
--- Comment #4 from Andrew Macleod <amacleod at redhat dot com> ---
The IL generated is:
_1 = x_2(D) >> y_3(D);
_4 = _1 <= x_2(D);
return _4;
All that should be needed is for the right shift operator in range-ops to
implement lhs_op1_relation() to indicate that if the range of op2 is >=0, then
return LE_EXPR.
this will automatically register the relation _1 <= x_2 at the def point for
_1, and then _4 should simply fold away as true.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
` (5 preceding siblings ...)
2022-01-12 2:00 ` amacleod at redhat dot com
@ 2022-01-13 18:52 ` cvs-commit at gcc dot gnu.org
2022-01-13 18:52 ` amacleod at redhat dot com
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-01-13 18:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Andrew Macleod <amacleod@gcc.gnu.org>:
https://gcc.gnu.org/g:27e4260166950b784fe270ba4f0cae9a66faf1c4
commit r12-6558-g27e4260166950b784fe270ba4f0cae9a66faf1c4
Author: Andrew MacLeod <amacleod@redhat.com>
Date: Wed Jan 12 13:28:55 2022 -0500
Add relation to unsigned right shift.
If the first operand and the shift value of a right shift operation are
both
>= 0, then we know the LHS of the operation is <= the first operand.
PR tree-optimization/96707
gcc/
* range-op.cc (operator_rshift::lhs_op1_relation): New.
gcc/testsuite/
* g++.dg/pr96707.C: New.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/96707] Failure to optimize right shift+unsigned compare of two variables optimally
2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
` (6 preceding siblings ...)
2022-01-13 18:52 ` cvs-commit at gcc dot gnu.org
@ 2022-01-13 18:52 ` amacleod at redhat dot com
7 siblings, 0 replies; 9+ messages in thread
From: amacleod at redhat dot com @ 2022-01-13 18:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96707
Andrew Macleod <amacleod at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #6 from Andrew Macleod <amacleod at redhat dot com> ---
fixed.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2020-08-19 13:03 [Bug tree-optimization/96707] New: Failure to optimize right shift+unsigned compare of two variables optimally gabravier at gmail dot com
2020-08-19 13:08 ` [Bug tree-optimization/96707] " gabravier at gmail dot com
2020-08-24 22:32 ` pinskia at gcc dot gnu.org
2020-08-25 11:07 ` rguenth at gcc dot gnu.org
2021-01-02 9:14 ` jakub at gcc dot gnu.org
2021-01-04 15:00 ` amacleod at redhat dot com
2022-01-12 2:00 ` amacleod at redhat dot com
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