http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57601
Bug ID: 57601
Summary: Vector lowering could use larger modes
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: glisse at gcc dot gnu.org
Target: x86_64-linux-gnu
typedef int vec __attribute__((vector_size(2*sizeof(int))));
vec f(vec a, vec b){
return a-b;
}
vmovq %xmm0, %rcx
vmovq %xmm1, %rdx
movl %ecx, %eax
shrq $32, %rcx
subl %edx, %eax
shrq $32, %rdx
subl %edx, %ecx
vmovd %eax, %xmm2
vpinsrd $1, %ecx, %xmm2, %xmm0
(with -Ofast -mavx2) whereas if I change the size to 4, I get:
vpsubd %xmm1, %xmm0, %xmm0
which seems valid to me even for size 2. It is not clear to me how to model
that at tree level, maybe it would be easier to just implement V2SI operations
in the backend?
