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[InstCombine] enhance (select X, C1, C2 --> ext X) to handle vectors
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By replacing dyn_cast of ConstantInt with m_Zero/m_One/m_AllOnes, we
allow these transforms for splat vectors.

Differential Revision: http://reviews.llvm.org/D21899

llvm-svn: 274696
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@rotateright
rotateright committed Jul 6, 2016
1 parent c1c6823 commit 65a51c2
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Showing 2 changed files with 46 additions and 27 deletions.
50 changes: 28 additions & 22 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View file
Expand Up @@ -954,32 +954,38 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
return BinaryOperator::CreateOr(TrueVal, FalseVal);
}

// Selecting between two integer constants?
if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
// select C, 1, 0 -> zext C to int
if (FalseValC->isZero() && TrueValC->getValue() == 1)
return new ZExtInst(CondVal, SI.getType());

// select C, -1, 0 -> sext C to int
if (FalseValC->isZero() && TrueValC->isAllOnesValue())
return new SExtInst(CondVal, SI.getType());

// select C, 0, 1 -> zext !C to int
if (TrueValC->isZero() && FalseValC->getValue() == 1) {
Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
return new ZExtInst(NotCond, SI.getType());
}
// Selecting between two integer or vector splat integer constants?
//
// Note that we don't handle a scalar select of vectors:
// select i1 %c, <2 x i8> <1, 1>, <2 x i8> <0, 0>
// because that may need 3 instructions to splat the condition value:
// extend, insertelement, shufflevector.
if (CondVal->getType()->isVectorTy() == SI.getType()->isVectorTy()) {
// select C, 1, 0 -> zext C to int
if (match(TrueVal, m_One()) && match(FalseVal, m_Zero()))
return new ZExtInst(CondVal, SI.getType());

// select C, -1, 0 -> sext C to int
if (match(TrueVal, m_AllOnes()) && match(FalseVal, m_Zero()))
return new SExtInst(CondVal, SI.getType());

// select C, 0, 1 -> zext !C to int
if (match(TrueVal, m_Zero()) && match(FalseVal, m_One())) {
Value *NotCond = Builder->CreateNot(CondVal, "not." + CondVal->getName());
return new ZExtInst(NotCond, SI.getType());
}

// select C, 0, -1 -> sext !C to int
if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
return new SExtInst(NotCond, SI.getType());
}
// select C, 0, -1 -> sext !C to int
if (match(TrueVal, m_Zero()) && match(FalseVal, m_AllOnes())) {
Value *NotCond = Builder->CreateNot(CondVal, "not." + CondVal->getName());
return new SExtInst(NotCond, SI.getType());
}
}

if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal))
if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
return replaceInstUsesWith(SI, V);
}

// See if we are selecting two values based on a comparison of the two values.
if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
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23 changes: 18 additions & 5 deletions llvm/test/Transforms/InstCombine/apint-select.ll
View file
Expand Up @@ -41,11 +41,11 @@ define i999 @not_sext(i1 %C) {
ret i999 %V
}

; FIXME: Vector selects of vector splat constants match APInt too.
; Vector selects of vector splat constants match APInt too.

define <2 x i41> @zext_vec(<2 x i1> %C) {
; CHECK-LABEL: @zext_vec(
; CHECK-NEXT: [[V:%.*]] = select <2 x i1> %C, <2 x i41> <i41 1, i41 1>, <2 x i41> zeroinitializer
; CHECK-NEXT: [[V:%.*]] = zext <2 x i1> %C to <2 x i41>
; CHECK-NEXT: ret <2 x i41> [[V]]
;
%V = select <2 x i1> %C, <2 x i41> <i41 1, i41 1>, <2 x i41> <i41 0, i41 0>
Expand All @@ -54,7 +54,7 @@ define <2 x i41> @zext_vec(<2 x i1> %C) {

define <2 x i32> @sext_vec(<2 x i1> %C) {
; CHECK-LABEL: @sext_vec(
; CHECK-NEXT: [[V:%.*]] = select <2 x i1> %C, <2 x i32> <i32 -1, i32 -1>, <2 x i32> zeroinitializer
; CHECK-NEXT: [[V:%.*]] = sext <2 x i1> %C to <2 x i32>
; CHECK-NEXT: ret <2 x i32> [[V]]
;
%V = select <2 x i1> %C, <2 x i32> <i32 -1, i32 -1>, <2 x i32> <i32 0, i32 0>
Expand All @@ -63,7 +63,8 @@ define <2 x i32> @sext_vec(<2 x i1> %C) {

define <2 x i999> @not_zext_vec(<2 x i1> %C) {
; CHECK-LABEL: @not_zext_vec(
; CHECK-NEXT: [[V:%.*]] = select <2 x i1> %C, <2 x i999> zeroinitializer, <2 x i999> <i999 1, i999 1>
; CHECK-NEXT: [[TMP1:%.*]] = zext <2 x i1> %C to <2 x i999>
; CHECK-NEXT: [[V:%.*]] = xor <2 x i999> [[TMP1]], <i999 1, i999 1>
; CHECK-NEXT: ret <2 x i999> [[V]]
;
%V = select <2 x i1> %C, <2 x i999> <i999 0, i999 0>, <2 x i999> <i999 1, i999 1>
Expand All @@ -72,13 +73,25 @@ define <2 x i999> @not_zext_vec(<2 x i1> %C) {

define <2 x i64> @not_sext_vec(<2 x i1> %C) {
; CHECK-LABEL: @not_sext_vec(
; CHECK-NEXT: [[V:%.*]] = select <2 x i1> %C, <2 x i64> zeroinitializer, <2 x i64> <i64 -1, i64 -1>
; CHECK-NEXT: [[NOT_C:%.*]] = xor <2 x i1> %C, <i1 true, i1 true>
; CHECK-NEXT: [[V:%.*]] = sext <2 x i1> [[NOT_C]] to <2 x i64>
; CHECK-NEXT: ret <2 x i64> [[V]]
;
%V = select <2 x i1> %C, <2 x i64> <i64 0, i64 0>, <2 x i64> <i64 -1, i64 -1>
ret <2 x i64> %V
}

; But don't touch this - we would need 3 instructions to extend and splat the scalar select condition.

define <2 x i32> @scalar_select_of_vectors(i1 %c) {
; CHECK-LABEL: @scalar_select_of_vectors(
; CHECK-NEXT: [[V:%.*]] = select i1 %c, <2 x i32> <i32 1, i32 1>, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[V]]
;
%V = select i1 %c, <2 x i32> <i32 1, i32 1>, <2 x i32> zeroinitializer
ret <2 x i32> %V
}

;; (x <s 0) ? -1 : 0 -> ashr x, 31

define i41 @test3(i41 %X) {
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