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.
