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Change instcombine's getShuffleMask to represent undef with negative values.

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This code had previously used 2*N, where N is the mask length, to represent
undef.  That is not safe because the shufflevector operands may have more
than N elements -- they don't have to match the result type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117721 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson 2010-10-29 22:03:05 +00:00
parent 46455096be
commit 822cb58d08
2 changed files with 49 additions and 40 deletions
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76
lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -53,22 +53,20 @@ static bool CheapToScalarize(Value *V, bool isConstant) {
return false;
}
/// Read and decode a shufflevector mask.
///
/// It turns undef elements into values that are larger than the number of
/// elements in the input.
static std::vector<unsigned> getShuffleMask(const ShuffleVectorInst *SVI) {
/// getShuffleMask - Read and decode a shufflevector mask.
/// Turn undef elements into negative values.
static std::vector<int> getShuffleMask(const ShuffleVectorInst *SVI) {
unsigned NElts = SVI->getType()->getNumElements();
if (isa<ConstantAggregateZero>(SVI->getOperand(2)))
return std::vector<unsigned>(NElts, 0);
return std::vector<int>(NElts, 0);
if (isa<UndefValue>(SVI->getOperand(2)))
return std::vector<unsigned>(NElts, 2*NElts);
return std::vector<int>(NElts, -1);
std::vector<unsigned> Result;
std::vector<int> Result;
const ConstantVector *CP = cast<ConstantVector>(SVI->getOperand(2));
for (User::const_op_iterator i = CP->op_begin(), e = CP->op_end(); i!=e; ++i)
if (isa<UndefValue>(*i))
Result.push_back(NElts*2); // undef -> 8
Result.push_back(-1); // undef
else
Result.push_back(cast<ConstantInt>(*i)->getZExtValue());
return Result;
@ -109,14 +107,13 @@ static Value *FindScalarElement(Value *V, unsigned EltNo) {
if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V)) {
unsigned LHSWidth =
cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
unsigned InEl = getShuffleMask(SVI)[EltNo];
if (InEl < LHSWidth)
return FindScalarElement(SVI->getOperand(0), InEl);
else if (InEl < LHSWidth*2)
return FindScalarElement(SVI->getOperand(1), InEl - LHSWidth);
else
cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
int InEl = getShuffleMask(SVI)[EltNo];
if (InEl < 0)
return UndefValue::get(PTy->getElementType());
if (InEl < (int)LHSWidth)
return FindScalarElement(SVI->getOperand(0), InEl);
return FindScalarElement(SVI->getOperand(1), InEl - LHSWidth);
}
// Otherwise, we don't know.
@ -215,18 +212,18 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
// If this is extracting an element from a shufflevector, figure out where
// it came from and extract from the appropriate input element instead.
if (ConstantInt *Elt = dyn_cast<ConstantInt>(EI.getOperand(1))) {
unsigned SrcIdx = getShuffleMask(SVI)[Elt->getZExtValue()];
int SrcIdx = getShuffleMask(SVI)[Elt->getZExtValue()];
Value *Src;
unsigned LHSWidth =
cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
if (SrcIdx < LHSWidth)
if (SrcIdx < 0)
return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
if (SrcIdx < (int)LHSWidth)
Src = SVI->getOperand(0);
else if (SrcIdx < LHSWidth*2) {
else {
SrcIdx -= LHSWidth;
Src = SVI->getOperand(1);
} else {
return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
}
return ExtractElementInst::Create(Src,
ConstantInt::get(Type::getInt32Ty(EI.getContext()),
@ -440,7 +437,7 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
Value *LHS = SVI.getOperand(0);
Value *RHS = SVI.getOperand(1);
std::vector<unsigned> Mask = getShuffleMask(&SVI);
std::vector<int> Mask = getShuffleMask(&SVI);
bool MadeChange = false;
@ -472,12 +469,12 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
// Remap any references to RHS to use LHS.
std::vector<Constant*> Elts;
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] >= 2*e)
if (Mask[i] < 0)
Elts.push_back(UndefValue::get(Type::getInt32Ty(SVI.getContext())));
else {
if ((Mask[i] >= e && isa<UndefValue>(RHS)) ||
(Mask[i] < e && isa<UndefValue>(LHS))) {
Mask[i] = 2*e; // Turn into undef.
if ((Mask[i] >= (int)e && isa<UndefValue>(RHS)) ||
(Mask[i] < (int)e && isa<UndefValue>(LHS))) {
Mask[i] = -1; // Turn into undef.
Elts.push_back(UndefValue::get(Type::getInt32Ty(SVI.getContext())));
} else {
Mask[i] = Mask[i] % e; // Force to LHS.
@ -498,9 +495,9 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
bool isLHSID = true, isRHSID = true;
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] >= e*2) continue; // Ignore undef values.
if (Mask[i] < 0) continue; // Ignore undef values.
// Is this an identity shuffle of the LHS value?
isLHSID &= (Mask[i] == i);
isLHSID &= (Mask[i] == (int)i);
// Is this an identity shuffle of the RHS value?
isRHSID &= (Mask[i]-e == i);
@ -521,19 +518,21 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
// turning: (splat(splat)) -> splat.
if (ShuffleVectorInst *LHSSVI = dyn_cast<ShuffleVectorInst>(LHS)) {
if (isa<UndefValue>(RHS)) {
std::vector<unsigned> LHSMask = getShuffleMask(LHSSVI);
std::vector<int> LHSMask = getShuffleMask(LHSSVI);
if (LHSMask.size() == Mask.size()) {
std::vector<unsigned> NewMask;
std::vector<int> NewMask;
bool isSplat = true;
unsigned SplatElt = 2 * Mask.size(); // undef
int SplatElt = -1; // undef
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
unsigned MaskElt = 2 * e; // undef
if (Mask[i] < e)
int MaskElt;
if (Mask[i] < 0 || Mask[i] >= (int)e)
MaskElt = -1; // undef
else
MaskElt = LHSMask[Mask[i]];
// Check if this could still be a splat.
if (MaskElt < 2*e) {
if (SplatElt < 2*e && SplatElt != MaskElt)
if (MaskElt >= 0) {
if (SplatElt >=0 && SplatElt != MaskElt)
isSplat = false;
SplatElt = MaskElt;
}
@ -543,13 +542,10 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
// If the result mask is equal to the src shuffle or this
// shuffle mask, do the replacement.
if (isSplat || NewMask == LHSMask || NewMask == Mask) {
unsigned LHSInNElts =
cast<VectorType>(LHSSVI->getOperand(0)->getType())->
getNumElements();
std::vector<Constant*> Elts;
const Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
for (unsigned i = 0, e = NewMask.size(); i != e; ++i) {
if (NewMask[i] >= LHSInNElts*2) {
if (NewMask[i] < 0) {
Elts.push_back(UndefValue::get(Int32Ty));
} else {
Elts.push_back(ConstantInt::get(Int32Ty, NewMask[i]));

13
test/Transforms/InstCombine/vec_shuffle.ll
View File

@ -88,6 +88,19 @@ define <4 x i8> @test9(<16 x i8> %tmp6) nounwind {
ret <4 x i8> %tmp9
}
; Same as test9, but make sure that "undef" mask values are not confused with
; mask values of 2*N, where N is the mask length. These shuffles should not
; be folded (because [8,9,4,8] may not be a mask supported by the target).
define <4 x i8> @test9a(<16 x i8> %tmp6) nounwind {
; CHECK: @test9a
; CHECK-NEXT: shufflevector
; CHECK-NEXT: shufflevector
; CHECK-NEXT: ret
%tmp7 = shufflevector <16 x i8> %tmp6, <16 x i8> undef, <4 x i32> < i32 undef, i32 9, i32 4, i32 8 > ; <<4 x i8>> [#uses=1]
%tmp9 = shufflevector <4 x i8> %tmp7, <4 x i8> undef, <4 x i32> < i32 3, i32 1, i32 2, i32 0 > ; <<4 x i8>> [#uses=1]
ret <4 x i8> %tmp9
}
; Redundant vector splats should be removed. Radar 8597790.
define <4 x i32> @test10(<4 x i32> %tmp5) nounwind {
; CHECK: @test10