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fix the BuildVector -> unpcklps logic to not do pointless shuffles

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when the top elements of a vector are undefined.  This happens all
the time for X86-64 ABI stuff because only the low 2 elements of
a 4 element vector are defined.  For example, on:

_Complex float f32(_Complex float A, _Complex float B) {
  return A+B;
}

We used to produce (with SSE2, SSE4.1+ uses insertps):

_f32:                                   ## @f32
	movdqa	%xmm0, %xmm2
	addss	%xmm1, %xmm2
	pshufd	$16, %xmm2, %xmm2
	pshufd	$1, %xmm1, %xmm1
	pshufd	$1, %xmm0, %xmm0
	addss	%xmm1, %xmm0
	pshufd	$16, %xmm0, %xmm1
	movdqa	%xmm2, %xmm0
	unpcklps	%xmm1, %xmm0
	ret

We now produce:

_f32:                                   ## @f32
	movdqa	%xmm0, %xmm2
	addss	%xmm1, %xmm2
	pshufd	$1, %xmm1, %xmm1
	pshufd	$1, %xmm0, %xmm3
	addss	%xmm1, %xmm3
	movaps	%xmm2, %xmm0
	unpcklps	%xmm3, %xmm0
	ret

This implements rdar://8368414


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112378 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-08-28 17:28:30 +00:00
parent 6e80e44926
commit 3ddcc43040
2 changed files with 36 additions and 1 deletions
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12
lib/Target/X86/X86ISelLowering.cpp
View File

@ -4304,8 +4304,18 @@ X86TargetLowering::LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const {
// Step 2: unpcklps X, Y ==> <3, 2, 1, 0>
unsigned EltStride = NumElems >> 1;
while (EltStride != 0) {
for (unsigned i = 0; i < EltStride; ++i)
for (unsigned i = 0; i < EltStride; ++i) {
// If V[i+EltStride] is undef and this is the first round of mixing,
// then it is safe to just drop this shuffle: V[i] is already in the
// right place, the one element (since it's the first round) being
// inserted as undef can be dropped. This isn't safe for successive
// rounds because they will permute elements within both vectors.
if (V[i+EltStride].getOpcode() == ISD::UNDEF &&
EltStride == NumElems/2)
continue;
V[i] = getUnpackl(DAG, dl, VT, V[i], V[i + EltStride]);
}
EltStride >>= 1;
}
return V[0];

25
test/CodeGen/X86/sse1.ll
View File

@ -18,3 +18,28 @@ define <8 x i16> @test2(<8 x i32> %a) nounwind {
; %c = sext <4 x i16> %a to <4 x i32> ; <<4 x i32>> [#uses=1]
; ret <4 x i32> %c
;}
; This should not emit shuffles to populate the top 2 elements of the 4-element
; vector that this ends up returning.
; rdar://8368414
define <2 x float> @test4(<2 x float> %A, <2 x float> %B) nounwind {
entry:
%tmp7 = extractelement <2 x float> %A, i32 0
%tmp5 = extractelement <2 x float> %A, i32 1
%tmp3 = extractelement <2 x float> %B, i32 0
%tmp1 = extractelement <2 x float> %B, i32 1
%add.r = fadd float %tmp7, %tmp3
%add.i = fsub float %tmp5, %tmp1
%tmp11 = insertelement <2 x float> undef, float %add.r, i32 0
%tmp9 = insertelement <2 x float> %tmp11, float %add.i, i32 1
ret <2 x float> %tmp9
; CHECK: test4:
; CHECK-NOT: shufps $16
; CHECK: shufps $1,
; CHECK-NOT: shufps $16
; CHECK: shufps $1,
; CHECK-NOT: shufps $16
; CHECK: unpcklps
; CHECK-NOT: shufps $16
; CHECK: ret
}