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* [Bug target/106420] New: Missed optimization for comparisons
@ 2022-07-23 9:25 zero at smallinteger dot com
2022-07-23 9:38 ` [Bug target/106420] " zero at smallinteger dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: zero at smallinteger dot com @ 2022-07-23 9:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106420
Bug ID: 106420
Summary: Missed optimization for comparisons
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: zero at smallinteger dot com
Target Milestone: ---
Created attachment 53339
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53339&action=edit
Sample code
When comparing different variables to the same constants, in some cases the
compiler could first combine the variables and then do a single compare. In
the sample given, two variables are compared against 7. In the slow path, GCC
produces the following with -O2.
cmp edi, 7
setg al
cmp esi, 7
setg dl
or eax, edx
movzx eax, al
ret
In the fast path, GCC produces this instead.
or edi, esi
xor eax, eax
cmp edi, 7
setg al
ret
Although the expression a > 7 || b > 7 is the same as (a | b) > 7, the latter
is better because it results in fewer instructions. A quick experiment shows
the latter also runs quite faster.
Verified with Godbolt for GCC trunk. Clang, ICC, and MSVC latest versions also
miss this opportunity as per Godbolt.
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug target/106420] Missed optimization for comparisons 2022-07-23 9:25 [Bug target/106420] New: Missed optimization for comparisons zero at smallinteger dot com @ 2022-07-23 9:38 ` zero at smallinteger dot com 2022-07-25 2:12 ` [Bug tree-optimization/106420] " crazylht at gmail dot com ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: zero at smallinteger dot com @ 2022-07-23 9:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106420 --- Comment #1 from zero at smallinteger dot com --- (it should be possible to massage the output further to use test and setne, which ICC prefers to e.g. cmp and seta) ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/106420] Missed optimization for comparisons 2022-07-23 9:25 [Bug target/106420] New: Missed optimization for comparisons zero at smallinteger dot com 2022-07-23 9:38 ` [Bug target/106420] " zero at smallinteger dot com @ 2022-07-25 2:12 ` crazylht at gmail dot com 2022-07-25 2:23 ` pinskia at gcc dot gnu.org 2022-07-25 2:35 ` zero at smallinteger dot com 3 siblings, 0 replies; 5+ messages in thread From: crazylht at gmail dot com @ 2022-07-25 2:12 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106420 Hongtao.liu <crazylht at gmail dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |crazylht at gmail dot com --- Comment #2 from Hongtao.liu <crazylht at gmail dot com> --- > Although the expression a > 7 || b > 7 is the same as (a | b) > 7, the Shoudn't the optimization be available for unsigned type only? ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/106420] Missed optimization for comparisons 2022-07-23 9:25 [Bug target/106420] New: Missed optimization for comparisons zero at smallinteger dot com 2022-07-23 9:38 ` [Bug target/106420] " zero at smallinteger dot com 2022-07-25 2:12 ` [Bug tree-optimization/106420] " crazylht at gmail dot com @ 2022-07-25 2:23 ` pinskia at gcc dot gnu.org 2022-07-25 2:35 ` zero at smallinteger dot com 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-07-25 2:23 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106420 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This can only be done for unsigned types as if either one was negative, then the check becames invalid. It is already done since GCC 11 (most likely the patch which fixed PR 95731). So this is invalid. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/106420] Missed optimization for comparisons 2022-07-23 9:25 [Bug target/106420] New: Missed optimization for comparisons zero at smallinteger dot com ` (2 preceding siblings ...) 2022-07-25 2:23 ` pinskia at gcc dot gnu.org @ 2022-07-25 2:35 ` zero at smallinteger dot com 3 siblings, 0 replies; 5+ messages in thread From: zero at smallinteger dot com @ 2022-07-25 2:35 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106420 --- Comment #4 from zero at smallinteger dot com --- Sorry about that :/. ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-07-25 2:35 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-07-23 9:25 [Bug target/106420] New: Missed optimization for comparisons zero at smallinteger dot com 2022-07-23 9:38 ` [Bug target/106420] " zero at smallinteger dot com 2022-07-25 2:12 ` [Bug tree-optimization/106420] " crazylht at gmail dot com 2022-07-25 2:23 ` pinskia at gcc dot gnu.org 2022-07-25 2:35 ` zero at smallinteger dot com
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