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

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

1 files changed, 25 insertions, 0 deletions

diff --git a/test/CodeGen/X86/sse1.ll b/test/CodeGen/X86/sse1.ll
index 6e7aad84de..73f88aec64 100644
--- a/test/CodeGen/X86/sse1.ll
+++ b/test/CodeGen/X86/sse1.ll
@@ -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
+}