https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117014
Bug ID: 117014
Summary: missed vectorization opportunity
Product: gcc
Version: 15.0
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, we noticed that there seems to be a missing vectorization for the code
below.
reduced code: https://godbolt.org/z/YaEPdWM3n
int data[100];
void f(int arr1[100], int arr2[100])
{
for(int i = 0; i < 100; i++){
arr2[i] = -arr1[i];
int k = arr1[i] + arr2[i];
data[i] = data[i + k] + 1;
}
}
GCC -O3 -fno-vect-cost-model -fwrapv:
f(int*, int*):
xor eax, eax
.L2:
mov ecx, DWORD PTR [rdi+rax*4]
mov edx, ecx
neg edx
mov DWORD PTR [rsi+rax*4], edx
mov edx, eax
sub edx, ecx
add edx, DWORD PTR [rdi+rax*4]
movsx rdx, edx
mov edx, DWORD PTR data[0+rdx*4]
add edx, 1
mov DWORD PTR data[0+rax*4], edx
add rax, 1
cmp rax, 100
jne .L2
ret
Possibly due to omission: _8 = _7 + _26; ==> _8 = i_22
_4 = MEM[(int *)arr1_15(D) + ivtmp.5_21 * 4];
_6 = -_4;
MEM[(int *)arr2_16(D) + ivtmp.5_21 * 4] = _6;
# DEBUG BEGIN_STMT
_7 = MEM[(int *)arr1_15(D) + ivtmp.5_21 * 4];
# DEBUG D#1 => -_4
# DEBUG k => _7 + D#1
# DEBUG BEGIN_STMT
_26 = i_22 - _4;
_8 = _7 + _26;
_9 = data[_8];
Expected code: vectorize the loop body.
For example, when assign k=0 directly ('int k = 0;'), gcc:
f(int*, int*):
lea rdx, [rdi+4]
mov eax, OFFSET FLAT:data
sub rax, rdx
cmp rax, 8
mov rax, rsi
seta cl
sub rax, rdx
cmp rax, 8
seta al
test cl, al
je .L5
mov rax, rsi
sub rax, OFFSET FLAT:data-15
cmp rax, 30
jbe .L5
pcmpeqd xmm1, xmm1
xor eax, eax
psrld xmm1, 31
.L3:
movdqu xmm3, XMMWORD PTR [rdi+rax]
pxor xmm0, xmm0
psubd xmm0, xmm3
movups XMMWORD PTR [rsi+rax], xmm0
movdqa xmm0, XMMWORD PTR data[rax]
add rax, 16
paddd xmm0, xmm1
movaps XMMWORD PTR data[rax-16], xmm0
cmp rax, 400
jne .L3
ret
.L5:
xor eax, eax
.L2:
mov edx, DWORD PTR [rdi+rax]
neg edx
mov DWORD PTR [rsi+rax], edx
add DWORD PTR data[rax], 1
add rax, 4
cmp rax, 400
jne .L2
ret
Thank you very much for your time and effort! We look forward to hearing from
you.
