https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84106
Bug ID: 84106
Summary: gcc is not able to vectorize code for 1D array, but
does so for 2D array of the same size
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bugzi...@poradnik-webmastera.com
Target Milestone: ---
[code]
#define N 9
int a1[N][N];
int a2[N][N];
int b1[N*N];
int b2[N*N];
void test1()
{
for (int i = 0; i < N; ++i)
{
for (int j = 0; j < N; ++j)
{
a2[i][j] = a1[i][j];
}
}
}
void test2()
{
for (int i = 0; i < N*N; ++i)
{
b2[i] = b1[i];
}
}
[/code]
This code compiled using gcc 8.0 (trunk) with "-O3 -mavx2" produces following
result. For some reason gcc is not able to vectorize code for test2 function. I
also tried to add "__attribute__((aligned(32)))" to all arrays, but it did not
help.
Similar code is also generated when compiling with "-O3 -mavx512f -mavx512vl
-mavx512bw -mavx512dq -mavx512cd" - gcc still generates code which uses YMM
registers, instead of ZMM ones.
[out]
test1():
vmovdqa ymm0, YMMWORD PTR a1[rip]
vmovdqa ymm1, YMMWORD PTR a1[rip+32]
vmovdqa ymm2, YMMWORD PTR a1[rip+64]
vmovdqa ymm3, YMMWORD PTR a1[rip+96]
vmovdqa YMMWORD PTR a2[rip], ymm0
vmovdqa ymm4, YMMWORD PTR a1[rip+128]
vmovdqa ymm5, YMMWORD PTR a1[rip+160]
vmovdqa YMMWORD PTR a2[rip+32], ymm1
vmovdqa ymm6, YMMWORD PTR a1[rip+192]
vmovdqa ymm7, YMMWORD PTR a1[rip+224]
vmovdqa ymm0, YMMWORD PTR a1[rip+256]
vmovdqa ymm1, YMMWORD PTR a1[rip+288]
vmovdqa YMMWORD PTR a2[rip+64], ymm2
mov eax, DWORD PTR a1[rip+320]
vmovdqa YMMWORD PTR a2[rip+96], ymm3
vmovdqa YMMWORD PTR a2[rip+128], ymm4
vmovdqa YMMWORD PTR a2[rip+160], ymm5
vmovdqa YMMWORD PTR a2[rip+192], ymm6
vmovdqa YMMWORD PTR a2[rip+224], ymm7
vmovdqa YMMWORD PTR a2[rip+256], ymm0
vmovdqa YMMWORD PTR a2[rip+288], ymm1
mov DWORD PTR a2[rip+320], eax
vzeroupper
ret
test2():
mov esi, OFFSET FLAT:b1
mov edi, OFFSET FLAT:b2
mov ecx, 40
rep movsq
mov eax, DWORD PTR [rsi]
mov DWORD PTR [rdi], eax
ret
b2:
.zero 324
b1:
.zero 324
a2:
.zero 324
a1:
.zero 324
[/out]
