+/// Given a bitcasted vector fed into an extract element instruction and then
+/// bitcasted again, eliminate at least one bitcast by changing the vector type
+/// of the extractelement instruction.
+/// Example:
+/// bitcast (extractelement (bitcast <2 x float> %X to <2 x i32>), 1) to float
+/// --->
+/// extractelement <2 x float> %X, i32 1
+static Instruction *foldBitCastExtElt(BitCastInst &BitCast, InstCombiner &IC,
+ const DataLayout &DL) {
+ // TODO: Create and use a pattern matcher for ExtractElementInst.
+ auto *ExtElt = dyn_cast<ExtractElementInst>(BitCast.getOperand(0));
+ if (!ExtElt || !ExtElt->hasOneUse())
+ return nullptr;
+
+ Value *InnerBitCast = nullptr;
+ if (!match(ExtElt->getOperand(0), m_BitCast(m_Value(InnerBitCast))))
+ return nullptr;
+
+ VectorType *VecType = cast<VectorType>(InnerBitCast->getType());
+ Type *DestType = BitCast.getType();
+
+ // If the element type of the vector doesn't match the result type,
+ // bitcast it to a vector type that we can extract from.
+ if (VecType->getElementType() != DestType) {
+ unsigned VecWidth = VecType->getPrimitiveSizeInBits();
+ unsigned DestWidth = DestType->getPrimitiveSizeInBits();
+ unsigned NumElts = VecWidth / DestWidth;
+ VecType = VectorType::get(DestType, NumElts);
+ InnerBitCast = IC.Builder->CreateBitCast(InnerBitCast, VecType, "bc");
+ }
+
+ return ExtractElementInst::Create(InnerBitCast, ExtElt->getOperand(1));
+}
+