http://llvm.org/bugs/show_bug.cgi?id=11210
Summary: [AVX] opportunity for better code with masked stores
Product: new-bugs
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
(Trying again, with description text this time).
Consider the following bitcode:
declare <8 x float> @llvm.x86.avx.maskload.ps.256(i8 *, <8 x float> %mask)
declare void @llvm.x86.avx.maskstore.ps.256(i8 *, <8 x float>, <8 x float>)
define void @foo(i8 * %ptr, <8 x float> %val, <8 x float> %mask) {
%v0 = call <8 x float> @llvm.x86.avx.maskload.ps.256(i8 * %ptr, <8 x float>
%mask)
%v1 = fadd <8 x float> %v0, %v0
call void @llvm.x86.avx.maskstore.ps.256(i8 * %ptr, <8 x float> %mask, <8 x
float> %val)
call void @llvm.x86.avx.maskstore.ps.256(i8 * %ptr, <8 x float> %mask, <8 x
float> %v1)
ret void
}
llc -mattr=+avx generates the following:
vmaskmovps (%rdi), %ymm1, %ymm2
vmaskmovps %ymm0, %ymm1, (%rdi)
vaddps %ymm2, %ymm2, %ymm0
vmaskmovps %ymm0, %ymm1, (%rdi)
Here, the first "vmaskmovps %ymm0, %ymm1, (%rdi)" instruction has no effect, as
the vmaskmovps after the vaddps overwrites the exact same locations (since it's
using the same mask as the first store).
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