Given the Altivec function:
vector unsigned short peepholebug(vector unsigned short a, vector unsigned
short b) {
vector unsigned short mask = (vector unsigned short)vec_cmplt(a, b);
if (vec_all_ge(a, b)) return a;
return mask;
}
XCode 2.2.1 / gcc 4.0 on PowerMac G5 generates ( with optimizer set to -os):
mfspr r0,256
stw r0,-8(r1)
oris r0,r0,0x8000
mtspr 256,r0
vcmpgtuh. v0,v3,v2
vcmpgtuh v0,v3,v2
beq cr6,L99
vor v2,v0,v0
lwz r12,-8(r1)
mtspr 256,r12
blr
Note the second "vcmpgtuh" instruction, which is completely superfluous. The
peephole optimizer should recognize this situation and remove the instruction.
(I've filed a bug with Apple; #4519214.)
--
Summary: Altivec Comparison Peephole Bug
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ben at shellandslate dot com
GCC build triplet: 4.0.0
GCC host triplet: 4.0.0
GCC target triplet: 4.0.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27212
