[InstCombine][SVE] Fix visitExtractElementInst for scalable type.

Summary:
This patch fix the following issues with visitExtractElementInst:

      1. Restrict VectorUtils::findScalarElement to fixed-length vector.
         For scalable type, the number of elements in shuffle mask is
         unknown at compile-time.
      2. Fix out-of-range calculation for fixed-length vector.
      3. Skip scalable type when analysis rely on fixed number of elements.
      4. Add unit tests to check functionality of extractelement for scalable type.

Reviewers: sdesmalen, efriedma, spatel, nikic

Reviewed By: efriedma

Subscribers: tschuett, hiraditya, rkruppe, psnobl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78267

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/VectorUtils.cpp b/llvm/lib/Analysis/VectorUtils.cpp
index a96686a..f16b04e 100644
--- a/llvm/lib/Analysis/VectorUtils.cpp
+++ b/llvm/lib/Analysis/VectorUtils.cpp
@@ -288,9 +288,11 @@ Value *llvm::findScalarElement(Value *V, unsigned EltNo) {
     return findScalarElement(III->getOperand(0), EltNo);
   }
 
-  if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V)) {
+  ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V);
+  // Restrict the following transformation to fixed-length vector.
+  if (SVI && isa<FixedVectorType>(SVI->getType())) {
     unsigned LHSWidth =
-        cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
+        cast<FixedVectorType>(SVI->getOperand(0)->getType())->getNumElements();
     int InEl = SVI->getMaskValue(EltNo);
     if (InEl < 0)
       return UndefValue::get(VTy->getElementType());