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Prefer shuffles to selects. Backends love shuffles!

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164763 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2012-09-27 08:33:56 +00:00
parent 37d3ef3140
commit 466e0f38d3
3 changed files with 55 additions and 2 deletions
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20
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -903,7 +903,7 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
return &SI;
}
if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
if (VectorType *VecTy = dyn_cast<VectorType>(SI.getType())) {
unsigned VWidth = VecTy->getNumElements();
APInt UndefElts(VWidth, 0);
APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
@ -912,6 +912,24 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
return ReplaceInstUsesWith(SI, V);
return &SI;
}
if (ConstantVector *CV = dyn_cast<ConstantVector>(CondVal)) {
// Form a shufflevector instruction.
SmallVector<Constant *, 8> Mask(VWidth);
Type *Int32Ty = Type::getInt32Ty(CV->getContext());
for (unsigned i = 0; i != VWidth; ++i) {
Constant *Elem = cast<Constant>(CV->getOperand(i));
if (ConstantInt *E = dyn_cast<ConstantInt>(Elem))
Mask[i] = ConstantInt::get(Int32Ty, i + (E->isZero() ? VWidth : 0));
else if (isa<UndefValue>(Elem))
Mask[i] = UndefValue::get(Int32Ty);
else
return 0;
}
Constant *MaskVal = ConstantVector::get(Mask);
Value *V = Builder->CreateShuffleVector(TrueVal, FalseVal, MaskVal);
return ReplaceInstUsesWith(SI, V);
}
}
return 0;

2
test/Transforms/InstCombine/vec_demanded_elts.ll
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@ -196,7 +196,7 @@ define <4 x float> @test_select(float %f, float %g) {
; CHECK-NOT: insertelement
; CHECK: %a3 = insertelement <4 x float> %a0, float 3.000000e+00, i32 3
; CHECK-NOT: insertelement
; CHECK: %ret = select <4 x i1> <i1 true, i1 false, i1 false, i1 true>, <4 x float> %a3, <4 x float> <float undef, float 4.000000e+00, float 5.000000e+00, float undef>
; CHECK: shufflevector <4 x float> %a3, <4 x float> <float undef, float 4.000000e+00, float 5.000000e+00, float undef>, <4 x i32> <i32 0, i32 5, i32 6, i32 3>
%a0 = insertelement <4 x float> undef, float %f, i32 0
%a1 = insertelement <4 x float> %a0, float 1.000000e+00, i32 1
%a2 = insertelement <4 x float> %a1, float 2.000000e+00, i32 2

35
test/Transforms/InstCombine/vec_shuffle.ll
View File

@ -153,3 +153,38 @@ define <8 x i8> @test12a(<8 x i8> %tmp6, <8 x i8> %tmp2) nounwind {
ret <8 x i8> %tmp3
}
; We should form a shuffle out of a select with constant condition.
define <4 x i16> @test13a(<4 x i16> %lhs, <4 x i16> %rhs) {
; CHECK: @test13a
; CHECK-NEXT: shufflevector <4 x i16> %lhs, <4 x i16> %rhs, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
; CHECK-NEXT: ret
%A = select <4 x i1> <i1 true, i1 false, i1 true, i1 false>,
<4 x i16> %lhs, <4 x i16> %rhs
ret <4 x i16> %A
}
define <4 x i16> @test13b(<4 x i16> %lhs, <4 x i16> %rhs) {
; CHECK: @test13b
; CHECK-NEXT: ret <4 x i16> %lhs
%A = select <4 x i1> <i1 true, i1 undef, i1 true, i1 true>,
<4 x i16> %lhs, <4 x i16> %rhs
ret <4 x i16> %A
}
define <4 x i16> @test13c(<4 x i16> %lhs, <4 x i16> %rhs) {
; CHECK: @test13c
; CHECK-NEXT: shufflevector <4 x i16> %lhs, <4 x i16> %rhs, <4 x i32> <i32 0, i32 undef, i32 2, i32 7>
; CHECK-NEXT: ret
%A = select <4 x i1> <i1 true, i1 undef, i1 true, i1 false>,
<4 x i16> %lhs, <4 x i16> %rhs
ret <4 x i16> %A
}
define <4 x i16> @test13d(<4 x i16> %lhs, <4 x i16> %rhs) {
; CHECK: @test13d
; CHECK: select
; CHECK-NEXT: ret
%A = select <4 x i1> <i1 true, i1 icmp ugt (<4 x i16>(<4 x i16>, <4 x i16>)* @test13a, <4 x i16>(<4 x i16>, <4 x i16>)* @test13b), i1 true, i1 false>,
<4 x i16> %lhs, <4 x i16> %rhs
ret <4 x i16> %A
}