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* [Bug middle-end/65474] New: sub-optimal code for __builtin_abs
@ 2015-03-19 19:21 wmi at google dot com
2015-03-19 22:53 ` [Bug target/65474] " wmi at google dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: wmi at google dot com @ 2015-03-19 19:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65474
Bug ID: 65474
Summary: sub-optimal code for __builtin_abs
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: wmi at google dot com
int foo(int x) {
return __builtin_abs(x);
}
~/workarea/gcc-r221398/build/install/bin/gcc -O2 -S 1.c -o 1.gcc.s
.cfi_startproc
movl %edi, %edx
movl %edi, %eax
sarl $31, %edx
xorl %edx, %eax
subl %edx, %eax
ret
.cfi_endproc
~/workarea/llvm-r224097/build/bin/clang -O2 -S 1.c -o 1.llvm.s
.cfi_startproc
movl %edi, %eax
negl %eax
cmovll %edi, %eax
retq
.cfi_endproc
^ permalink raw reply [flat|nested] 4+ messages in thread* [Bug target/65474] sub-optimal code for __builtin_abs 2015-03-19 19:21 [Bug middle-end/65474] New: sub-optimal code for __builtin_abs wmi at google dot com @ 2015-03-19 22:53 ` wmi at google dot com 2015-03-19 22:54 ` wmi at google dot com 2015-03-20 10:59 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: wmi at google dot com @ 2015-03-19 22:53 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65474 --- Comment #2 from wmi at google dot com --- Created attachment 35069 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35069&action=edit microbench ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/65474] sub-optimal code for __builtin_abs 2015-03-19 19:21 [Bug middle-end/65474] New: sub-optimal code for __builtin_abs wmi at google dot com 2015-03-19 22:53 ` [Bug target/65474] " wmi at google dot com @ 2015-03-19 22:54 ` wmi at google dot com 2015-03-20 10:59 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: wmi at google dot com @ 2015-03-19 22:54 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65474 --- Comment #3 from wmi at google dot com --- Thanks. You are right. I wrote a microbenchmark (attached), and tested it on different intel microarchitectures. westmere: 1.gcc.out: 19.42 1.llvm.out: 19.32 sandybridge: 1.gcc.out: 18.61 1.llvm.out: 19.16 ivybridge: 1.gcc.out: 15.79 1.llvm.out: 15.87 On sandybridge, llvm's version was slower. On other microarchitectures, they were close to each other. So gcc's choose makes sense. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/65474] sub-optimal code for __builtin_abs 2015-03-19 19:21 [Bug middle-end/65474] New: sub-optimal code for __builtin_abs wmi at google dot com 2015-03-19 22:53 ` [Bug target/65474] " wmi at google dot com 2015-03-19 22:54 ` wmi at google dot com @ 2015-03-20 10:59 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2015-03-20 10:59 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65474 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |WONTFIX --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- Thus wontfix. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2015-03-20 10:26 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2015-03-19 19:21 [Bug middle-end/65474] New: sub-optimal code for __builtin_abs wmi at google dot com 2015-03-19 22:53 ` [Bug target/65474] " wmi at google dot com 2015-03-19 22:54 ` wmi at google dot com 2015-03-20 10:59 ` rguenth at gcc dot gnu.org
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