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some notes about suboptimal insertps's

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107613 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-07-05 05:48:41 +00:00
parent 598751ed25
commit c06cbad141
1 changed files with 31 additions and 0 deletions
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31
lib/Target/X86/README-SSE.txt
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@ -846,3 +846,34 @@ This would be better kept in the SSE unit by treating XMM0 as a 4xfloat and
doing a shuffle from v[1] to v[0] then a float store.
//===---------------------------------------------------------------------===//
On SSE4 machines, we compile this code:
define <2 x float> @test2(<2 x float> %Q, <2 x float> %R,
<2 x float> *%P) nounwind {
%Z = fadd <2 x float> %Q, %R
store <2 x float> %Z, <2 x float> *%P
ret <2 x float> %Z
}
into:
_test2: ## @test2
## BB#0:
insertps $0, %xmm2, %xmm2
insertps $16, %xmm3, %xmm2
insertps $0, %xmm0, %xmm3
insertps $16, %xmm1, %xmm3
addps %xmm2, %xmm3
movq %xmm3, (%rdi)
movaps %xmm3, %xmm0
pshufd $1, %xmm3, %xmm1
## kill: XMM1<def> XMM1<kill>
ret
The insertps's of $0 are pointless complex copies.
//===---------------------------------------------------------------------===//