https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64909
Bug ID: 64909
Summary: [4.8/5 regression] Missed vectorization
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: hubicka at gcc dot gnu.org
Hi,
the following loop (taken from firefox unicode stuff)
unsigned short a[32];
unsigned int b[32];
t()
{
int i;
for (i=0;i<12;i++)
b[i]=a[i];
}
compiles by clang to:
t: # @t
.cfi_startproc
# BB#0:
vpmovzxwd a(%rip), %xmm0
vmovdqa .LCPI0_0(%rip), %xmm1 # xmm1 = [65535,65535,65535,65535]
vpand %xmm1, %xmm0, %xmm0
vmovdqa %xmm0, b(%rip)
vpmovzxwd a+8(%rip), %xmm0
vpand %xmm1, %xmm0, %xmm0
vmovdqa %xmm0, b+16(%rip)
vpmovzxwd a+16(%rip), %xmm0
vpand %xmm1, %xmm0, %xmm0
vmovdqa %xmm0, b+32(%rip)
retq
GCC 4.7 does:
t:
.LFB0:
.cfi_startproc
movzwl a+16(%rip), %eax
vmovaps a(%rip), %xmm0
vpmovzxwd %xmm0, %xmm1
vpsrldq $8, %xmm0, %xmm0
vpmovzxwd %xmm0, %xmm0
movl %eax, b+32(%rip)
movzwl a+18(%rip), %eax
vmovaps %xmm1, b(%rip)
vmovaps %xmm0, b+16(%rip)
movl %eax, b+36(%rip)
movzwl a+20(%rip), %eax
movl %eax, b+40(%rip)
movzwl a+22(%rip), %eax
movl %eax, b+44(%rip)
ret
while 4.8 and mainline unrolls and keeps it that way:
t:
.LFB0:
.cfi_startproc
movzwl a(%rip), %eax
movl %eax, b(%rip)
movzwl a+2(%rip), %eax
movl %eax, b+4(%rip)
movzwl a+4(%rip), %eax
movl %eax, b+8(%rip)
movzwl a+6(%rip), %eax
movl %eax, b+12(%rip)
movzwl a+8(%rip), %eax
movl %eax, b+16(%rip)
movzwl a+10(%rip), %eax
movl %eax, b+20(%rip)
movzwl a+12(%rip), %eax
movl %eax, b+24(%rip)
movzwl a+14(%rip), %eax
movl %eax, b+28(%rip)
movzwl a+16(%rip), %eax
movl %eax, b+32(%rip)
movzwl a+18(%rip), %eax
movl %eax, b+36(%rip)
movzwl a+20(%rip), %eax
movl %eax, b+40(%rip)
movzwl a+22(%rip), %eax
movl %eax, b+44(%rip)
ret
