[InstCombine] Gracefully handle out of range extractelement indices

InstSimplify is responsible for handling these, but we shouldn't just assert here.

Reduced from oss-fuzz #4808 test case

llvm-svn: 321489

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 65a96b96522..aeac8910af6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -181,11 +181,13 @@ Instruction *InstCombiner::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.
   if (ConstantInt *IdxC = dyn_cast<ConstantInt>(EI.getOperand(1))) {
-    unsigned IndexVal = IdxC->getZExtValue();
     unsigned VectorWidth = EI.getVectorOperandType()->getNumElements();
 
-    // InstSimplify handles cases where the index is invalid.
-    assert(IndexVal < VectorWidth);
+    // InstSimplify should handle cases where the index is invalid.
+    if (!IdxC->getValue().ule(VectorWidth))
+      return nullptr;
+
+    unsigned IndexVal = IdxC->getZExtValue();
 
     // 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