- Use PatternMatch

Author: kmclaughlin-arm

llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

@@ -419,7 +419,6 @@ Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
   // If extracting a specified index from the vector, see if we can recursively
   // find a previously computed scalar that was inserted into the vector.
   auto *IndexC = dyn_cast<ConstantInt>(Index);
-  auto *II = dyn_cast<IntrinsicInst>(SrcVec);
   bool HasKnownValidIndex = false;
   if (IndexC) {
     // Canonicalize type of constant indices to i64 to simplify CSE
@@ -430,7 +429,7 @@ Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
     unsigned NumElts = EC.getKnownMinValue();
     HasKnownValidIndex = IndexC->getValue().ult(NumElts);
 
-    if (II) {
+    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(SrcVec)) {
       Intrinsic::ID IID = II->getIntrinsicID();
       // Index needs to be lower than the minimum size of the vector, because
       // for scalable vector, the vector size is known at run time.
@@ -465,9 +464,10 @@ Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
 
   // If SrcVec is a subvector starting at index 0, extract from the
   // wider source vector
-  if (II && II->getIntrinsicID() == Intrinsic::vector_extract)
-    if (cast<ConstantInt>(II->getArgOperand(1))->isZero())
-      return ExtractElementInst::Create(II->getArgOperand(0), Index);
+  Value *V;
+  if (match(SrcVec,
+            m_Intrinsic<Intrinsic::vector_extract>(m_Value(V), m_Zero())))
+    return ExtractElementInst::Create(V, Index);
 
   // TODO come up with a n-ary matcher that subsumes both unary and
   // binary matchers.