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* [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore
@ 2022-04-14 13:47 denis.campredon at gmail dot com
2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: denis.campredon at gmail dot com @ 2022-04-14 13:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276
Bug ID: 105276
Summary: [12 Regression] executed once loop not optimized
anymore
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: denis.campredon at gmail dot com
Target Milestone: ---
bool foo(unsigned i) {
bool result = true;
while (i) {
i = i % 3;
i = i - (i==2 ? 2 : i ? 1 : 0);
result = !result;
}
return result;
}
--------------
compiled with g++ 11.2 and -O2 it produces:
-----------------
foo(unsigned int):
test edi, edi
sete al
ret
----------------
With current trunk and -02 lots of instructions are generated, the loop is
still present, about 30 instructions are produced.
Also, when compiled with -Os trunk produces loopless assembly:
------------------
foo(unsigned int):
mov dl, 1
test edi, edi
je .L1
xor edx, edx
.L1:
mov eax, edx
ret
-------------------
Whereas using -Os and g++ 11.2 it uses one less register:
------------------
foo(unsigned int):
mov al, 1
test edi, edi
je .L4
xor eax, eax
.L4:
ret
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore
2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com
@ 2022-04-19 8:29 ` rguenth at gcc dot gnu.org
2022-04-20 15:38 ` jakub at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-04-19 8:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization,
| |needs-bisection
Component|c |tree-optimization
Target Milestone|--- |12.0
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
likely jump threading changes
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore
2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com
2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org
@ 2022-04-20 15:38 ` jakub at gcc dot gnu.org
2022-04-21 15:46 ` amacleod at redhat dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-04-20 15:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|needs-bisection |
CC| |amacleod at redhat dot com,
| |jakub at gcc dot gnu.org
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2022-04-20
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r12-5688-gcb137e85720654e41db370d952df226654e576a6
The difference starts in vrp2, where the actual IL change is:
- _5 = (bool) i_16;
- _12 = i_16;
+ _5 = i_16 != 0;
+ _12 = (unsigned int) _5;
and the ranges changes are:
-i_1 : unsigned int [0, 1]
+i_1 : unsigned int [0, 2]
i_7 : unsigned int [0, 2]
-i_8 : unsigned int [0, 1][+INF, +INF]
+i_8 : unsigned int [0, 2][+INF, +INF]
_12 : unsigned int [0, 1]
i_13 : unsigned int [1, +INF]
-i_14 : unsigned int [1, 1][+INF, +INF]
-i_16 : unsigned int [0, 1]
+i_14 : unsigned int [1, 2][+INF, +INF]
+i_16 : unsigned int [0, 2]
The old ranges were narrower and I think correct.
i_7 = i_13 % 3;
...
if (i_7 != 2)
...
# i_16 = PHI <i_7(3), i_1(5)>
_5 = i_16 != 0;
_12 = (unsigned int) _5;
i_8 = i_16 - _12;
if (i_8 != 0)
...
# i_14 = PHI <i_8(4)>
i_1 = i_14 % 3;
Now, that
i = i % 3;
(i==2 ? 2 : i ? 1 : 0)
in the source is just an obfuscated way of saying i = i % 3; i
so obviously the loop will iterate at most once (0 times if i is 0, otherwise
there will be i = i - i; and it will be zero at the end of the first
iteration).
That is something the ranger doesn't need to decipher obviously, but the
above means i_7 is [0, 2], on i_16 PHI i_7 is known to be [0, 1], so assuming
it comes from that edge, i_8 is [0, 1][+INF, +INF] aka ~[2, 0xfffffffe],
for 0 it doesn't even jump to i_14 PHI (but 0 % 3 is 0), for i_14 == 1 is 1 % 3
1 and for i_14 == -1U is -1U % 3 == 0. So, i_1 is in [0, 1] range and loops,
so the original assumptions that i_16 is [0, 1] don't change.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore
2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com
2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org
2022-04-20 15:38 ` jakub at gcc dot gnu.org
@ 2022-04-21 15:46 ` amacleod at redhat dot com
2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org
2022-04-25 14:27 ` amacleod at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: amacleod at redhat dot com @ 2022-04-21 15:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276
--- Comment #3 from Andrew Macleod <amacleod at redhat dot com> ---
Created attachment 52848
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52848&action=edit
proposed patch
When I removed the recursion from range_of_stmt, I neglected to incorporate the
existing known global range for an ssa-name into the calculated value.
Range_of_stmt does this, but the prefill calculation missed it. This patch
fixes that oversight.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore
2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com
` (2 preceding siblings ...)
2022-04-21 15:46 ` amacleod at redhat dot com
@ 2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org
2022-04-25 14:27 ` amacleod at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-04-25 13:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276
--- Comment #4 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:362e2a9c6297203bcf7f66bfb51dffb82b42d3b3
commit r12-8246-g362e2a9c6297203bcf7f66bfb51dffb82b42d3b3
Author: Andrew MacLeod <amacleod@redhat.com>
Date: Mon Apr 25 09:56:35 2022 -0400
Retain existing range knowledge when prefilling statements.
When range_of_stmt was adjusted to avoid large recursion depth, we need to
intersect the calculated range whth the any known range to avoid losing
info. Range_of_stmt does this, but the new prefill code missed it.
PR tree-optimization/105276
gcc/
* gimple-range.cc (gimple_ranger::prefill_stmt_dependencies):
Include
existing global range with calculated value.
gcc/testsuite/
* g++.dg/pr105276.C: New.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore
2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com
` (3 preceding siblings ...)
2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org
@ 2022-04-25 14:27 ` amacleod at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: amacleod at redhat dot com @ 2022-04-25 14:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276
Andrew Macleod <amacleod at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #5 from Andrew Macleod <amacleod at redhat dot com> ---
fixed.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com
2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org
2022-04-20 15:38 ` jakub at gcc dot gnu.org
2022-04-21 15:46 ` amacleod at redhat dot com
2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org
2022-04-25 14:27 ` amacleod at redhat dot com
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