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* [Bug tree-optimization/114823] New: Missed optimization of redundant loops
@ 2024-04-23 10:11 652023330028 at smail dot nju.edu.cn
2024-04-23 15:53 ` [Bug tree-optimization/114823] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: 652023330028 at smail dot nju.edu.cn @ 2024-04-23 10:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114823
Bug ID: 114823
Summary: Missed optimization of redundant loops
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: 652023330028 at smail dot nju.edu.cn
Target Milestone: ---
Hello, for the reduced code below, its second loop is redundant. There seems to
be a missed optimization.
https://godbolt.org/z/McqeYdnfY
int a[1024];
int b[1024];
void func()
{
for (int i = 0; i < 1024; i+=1) {
a[i] = b[i] * 2;
}
for (int i = 0; i < 1024; i+=1) {
a[i] = b[i] * 2;
}
}
GCC -O3:
func:
xor eax, eax
.L2:
movdqa xmm0, XMMWORD PTR b[rax]
add rax, 16
pslld xmm0, 1
movaps XMMWORD PTR a[rax-16], xmm0
cmp rax, 4096
jne .L2
xor eax, eax
.L3:
movdqa xmm0, XMMWORD PTR b[rax]
add rax, 16
pslld xmm0, 1
movaps XMMWORD PTR a[rax-16], xmm0
cmp rax, 4096
jne .L3
ret
Expected code:
func:
xor eax, eax
.L2:
movdqa xmm0, XMMWORD PTR b[rax]
add rax, 16
pslld xmm0, 1
movaps XMMWORD PTR a[rax-16], xmm0
cmp rax, 4096
jne .L2
ret
Thank you very much for your time and effort! We look forward to hearing from
you.
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/114823] Missed optimization of redundant loops
2024-04-23 10:11 [Bug tree-optimization/114823] New: Missed optimization of redundant loops 652023330028 at smail dot nju.edu.cn
@ 2024-04-23 15:53 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-04-23 15:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114823
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Keywords| |missed-optimization
Ever confirmed|0 |1
Last reconfirmed| |2024-04-23
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. loop fusion would detect the redundancy.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2024-04-23 10:11 [Bug tree-optimization/114823] New: Missed optimization of redundant loops 652023330028 at smail dot nju.edu.cn
2024-04-23 15:53 ` [Bug tree-optimization/114823] " rguenth at gcc dot gnu.org
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