https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88547
Bug ID: 88547
Summary: missed optimization for vector comparisons
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: rth at gcc dot gnu.org
Target Milestone: ---
typedef signed svec __attribute__((vector_size(16)));
typedef unsigned uvec __attribute__((vector_size(16)));
svec les(svec x, svec y) {
return x <= y;
}
uvec leu(uvec x, uvec y) {
return x <= y;
}
currently assemble to
les:
vpcmpgtd %xmm1, %xmm0, %xmm0
vpcmpeqd %xmm1, %xmm1, %xmm1
vpandn %xmm1, %xmm0, %xmm0
leu:
vmovdqa64 .LC0(%rip), %xmm2
vpsubd %xmm2, %xmm1, %xmm1
vpsubd %xmm2, %xmm0, %xmm0
vpcmpgtd %xmm1, %xmm0, %xmm0
vpcmpeqd %xmm1, %xmm1, %xmm1
vpandn %xmm1, %xmm0, %xmm0
By using the transformation min(x, y) == x we can produce
les:
vpminsd %xmm1, %xmm0, %xmm1
vpcmpeqd %xmm1, %xmm0, %xmm0
leu:
vpminud %xmm1, %xmm0, %xmm1
vpcmpeqd %xmm0, %xmm1, %xmm0
This can be used to reduce unsigned comparisons without requiring
the use of a constant bias vector. At least when the given min insn
is available in the architecture.
