[PATCH] D40650: [InstSimplify] Fold insertelement into undef if index is out of bounds

[Igor Laevsky via Phabricator via llvm-commits]

igor-laevsky created this revision.

This is branched from the https://reviews.llvm.org/D40390.

According to the llvm ir specification insertelement with out of bounds index is undef. This change implements this rule for the InstSimplify. It's mostly valuable as a way to prevent accidental crashes in various passes which are not expecting such indexes.


https://reviews.llvm.org/D40650

Files:
  include/llvm/Analysis/InstructionSimplify.h
  lib/Analysis/InstructionSimplify.cpp


Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -3769,6 +3769,20 @@
   return ::SimplifyInsertValueInst(Agg, Val, Idxs, Q, RecursionLimit);
 }
 
+Value *llvm::SimplifyInsertElementInst(Value *Vec, Value *, Value *Idx,
+                                       const SimplifyQuery &) {
+  // Fold into undef if index is out of bounds
+  if (auto *CI = dyn_cast<ConstantInt>(Idx)) {
+    uint64_t IdxVal = CI->getZExtValue();
+    uint64_t NumElements = cast<VectorType>(Vec->getType())->getNumElements();
+
+    if (IdxVal <= NumElements)
+      return UndefValue::get(Vec->getType());
+  }
+
+  return nullptr;
+}
+
 /// Given operands for an ExtractValueInst, see if we can fold the result.
 /// If not, this returns null.
 static Value *SimplifyExtractValueInst(Value *Agg, ArrayRef<unsigned> Idxs,
@@ -4637,6 +4651,12 @@
                                      IV->getIndices(), Q);
     break;
   }
+  case Instruction::InsertElement: {
+    auto *IE = cast<InsertElementInst>(I);
+    Result = SimplifyInsertElementInst(IE->getOperand(0), IE->getOperand(1),
+                                       IE->getOperand(2), Q);
+    break;
+  }
   case Instruction::ExtractValue: {
     auto *EVI = cast<ExtractValueInst>(I);
     Result = SimplifyExtractValueInst(EVI->getAggregateOperand(),
Index: include/llvm/Analysis/InstructionSimplify.h
===================================================================
--- include/llvm/Analysis/InstructionSimplify.h
+++ include/llvm/Analysis/InstructionSimplify.h
@@ -161,6 +161,10 @@
 Value *SimplifyInsertValueInst(Value *Agg, Value *Val, ArrayRef<unsigned> Idxs,
                                const SimplifyQuery &Q);
 
+/// Given operands for an InsertElement, fold the result or return null.
+Value *SimplifyInsertElementInst(Value *Vec, Value *Elt, Value *Idx,
+                                 const SimplifyQuery &Q);
+
 /// Given operands for an ExtractValueInst, fold the result or return null.
 Value *SimplifyExtractValueInst(Value *Agg, ArrayRef<unsigned> Idxs,
                                 const SimplifyQuery &Q);


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