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Canonicalize insert/extractelement from single-element vectors into 

bitcasts.

It would also be possible to canonicalize the other way; does anyone 
have a preference?

llvm-svn: 76300
This commit is contained in:
Eli Friedman 2009-07-18 09:07:47 +00:00
parent fd16798b1f
commit a807aae226
2 changed files with 28 additions and 6 deletions
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22
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -12366,13 +12366,18 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
if (op0)
return ReplaceInstUsesWith(EI, op0);
}
unsigned VectorWidth =
cast<VectorType>(EI.getOperand(0)->getType())->getNumElements();
// Canonicalize extractelement from a vector of width 1 to a bitcast
if (VectorWidth == 1)
return new BitCastInst(EI.getOperand(0), EI.getType());
// If extracting a specified index from the vector, see if we can recursively
// find a previously computed scalar that was inserted into the vector.
if (ConstantInt *IdxC = dyn_cast<ConstantInt>(EI.getOperand(1))) {
unsigned IndexVal = IdxC->getZExtValue();
unsigned VectorWidth =
cast<VectorType>(EI.getOperand(0)->getType())->getNumElements();
// If this is extracting an invalid index, turn this into undef, to avoid
// crashing the code below.
@ -12382,7 +12387,7 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
// This instruction only demands the single element from the input vector.
// If the input vector has a single use, simplify it based on this use
// property.
if (EI.getOperand(0)->hasOneUse() && VectorWidth != 1) {
if (EI.getOperand(0)->hasOneUse()) {
APInt UndefElts(VectorWidth, 0);
APInt DemandedMask(VectorWidth, 1 << IndexVal);
if (Value *V = SimplifyDemandedVectorElts(EI.getOperand(0),
@ -12619,13 +12624,18 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
// Inserting an undef or into an undefined place, remove this.
if (isa<UndefValue>(ScalarOp) || isa<UndefValue>(IdxOp))
ReplaceInstUsesWith(IE, VecOp);
unsigned NumVectorElts = IE.getType()->getNumElements();
// Canonicalize insertelement into vector of width 1 to a bitcast
if (NumVectorElts == 1)
return new BitCastInst(IE.getOperand(1), IE.getType());
// If the inserted element was extracted from some other vector, and if the
// indexes are constant, try to turn this into a shufflevector operation.
if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)) {
if (isa<ConstantInt>(EI->getOperand(1)) && isa<ConstantInt>(IdxOp) &&
EI->getOperand(0)->getType() == IE.getType()) {
unsigned NumVectorElts = IE.getType()->getNumElements();
unsigned ExtractedIdx =
cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();

12
llvm/test/Transforms/InstCombine/vec-single-elt.ll Normal file
View File

@ -0,0 +1,12 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep element
; insert/extractelement should canonicalize to bitcast
define i64 @a(<1 x i64> %x) {
%r = extractelement <1 x i64> %x, i32 0
ret i64 %r
}
define <1 x i64> @b(i64 %x) {
%r = insertelement <1 x i64> undef, i64 %x, i32 0
ret <1 x i64> %r
}