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XCode 2.2.1 / gcc 4.0 Peephole Bug

Subject: XCode 2.2.1 / gcc 4.0 Peephole Bug
From: Ben Weiss <email@hidden>
Date: Wed, 19 Apr 2006 01:11:04 -0700
Delivered-to: email@hidden
Delivered-to: email@hidden

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 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.) Anyone know if more recent versions of gcc are able to do this? I have some bottleneck code that could seriously benefit from this, and I'd rather avoid assembly if I can...

Thanks,
Ben
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