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* [Bug tree-optimization/53979] New: (a^b^b) not simplified to (a) (in combination with CSE??)
@ 2012-07-16 10:41 vermaelen.wouter at gmail dot com
2020-06-03 3:18 ` [Bug tree-optimization/53979] ((a ^ b) | a) not optimized to (a | b) gabravier at gmail dot com
2021-07-28 22:19 ` pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: vermaelen.wouter at gmail dot com @ 2012-07-16 10:41 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53979
Bug #: 53979
Summary: (a^b^b) not simplified to (a) (in combination with
CSE??)
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: vermaelen.wouter@gmail.com
The following 3 functions should ideally generate identical code (and they do
when using clang).
int f1(int a, int b) {
int c = b;
return (a ^ b ^ c) | (a ^ b) | a;
}
int f2(int a, int b) {
return (a ^ b) | a;
}
int f3(int a, int b) {
return a | b;
}
I tested gcc revision trunk@189510 and it shows 2 missed optimizations:
1) (a ^ b ^ b) not simplified to (a)
Normally gcc performs this optimization, but I *guess* it misses it here
because of the CSE opportunity with (a ^ b).
2) ((a ^ b) | a) not simplified to (a | b)
Of course in this example it's easy to manually rewrite the code. But in my
original code this function was actually a template and for some instantiations
the expression for the variable 'c' simplified to just 'b'. So the first missed
optimization is something I saw in real code. The second missed optimization
only occurs in this (much) simplified variant of the function.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/53979] ((a ^ b) | a) not optimized to (a | b)
2012-07-16 10:41 [Bug tree-optimization/53979] New: (a^b^b) not simplified to (a) (in combination with CSE??) vermaelen.wouter at gmail dot com
@ 2020-06-03 3:18 ` gabravier at gmail dot com
2021-07-28 22:19 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: gabravier at gmail dot com @ 2020-06-03 3:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53979
Gabriel Ravier <gabravier at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |gabravier at gmail dot com
--- Comment #4 from Gabriel Ravier <gabravier at gmail dot com> ---
I've just checked on trunk and it looks fixed
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/53979] ((a ^ b) | a) not optimized to (a | b)
2012-07-16 10:41 [Bug tree-optimization/53979] New: (a^b^b) not simplified to (a) (in combination with CSE??) vermaelen.wouter at gmail dot com
2020-06-03 3:18 ` [Bug tree-optimization/53979] ((a ^ b) | a) not optimized to (a | b) gabravier at gmail dot com
@ 2021-07-28 22:19 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-28 22:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53979
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |7.0
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed for GCC 7.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-07-28 22:19 UTC | newest]
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2012-07-16 10:41 [Bug tree-optimization/53979] New: (a^b^b) not simplified to (a) (in combination with CSE??) vermaelen.wouter at gmail dot com
2020-06-03 3:18 ` [Bug tree-optimization/53979] ((a ^ b) | a) not optimized to (a | b) gabravier at gmail dot com
2021-07-28 22:19 ` pinskia at gcc dot gnu.org
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