IR: Properly return nullptr when getAggregateElement is out-of-bounds

We didn't properly handle the out-of-bounds case for
ConstantAggregateZero and UndefValue.  This would manifest as a crash
when the constant folder was asked to fold a load of a constant global
whose struct type has no operands.

This fixes PR22595.

llvm-svn: 229352

1 files changed, 19 insertions, 4 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 1d2602aef13..44052b22457 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -257,11 +257,11 @@ Constant *Constant::getAggregateElement(unsigned Elt) const {
   if (const ConstantVector *CV = dyn_cast<ConstantVector>(this))
     return Elt < CV->getNumOperands() ? CV->getOperand(Elt) : nullptr;
 
-  if (const ConstantAggregateZero *CAZ =dyn_cast<ConstantAggregateZero>(this))
-    return CAZ->getElementValue(Elt);
+  if (const ConstantAggregateZero *CAZ = dyn_cast<ConstantAggregateZero>(this))
+    return Elt < CAZ->getNumElements() ? CAZ->getElementValue(Elt) : nullptr;
 
   if (const UndefValue *UV = dyn_cast<UndefValue>(this))
-    return UV->getElementValue(Elt);
+    return Elt < UV->getNumElements() ? UV->getElementValue(Elt) : nullptr;
 
   if (const ConstantDataSequential *CDS =dyn_cast<ConstantDataSequential>(this))
     return Elt < CDS->getNumElements() ? CDS->getElementAsConstant(Elt)
@@ -764,6 +764,14 @@ Constant *ConstantAggregateZero::getElementValue(unsigned Idx) const {
   return getStructElement(Idx);
 }
 
+unsigned ConstantAggregateZero::getNumElements() const {
+  const Type *Ty = getType();
+  if (const auto *AT = dyn_cast<ArrayType>(Ty))
+    return AT->getNumElements();
+  if (const auto *VT = dyn_cast<VectorType>(Ty))
+    return VT->getNumElements();
+  return Ty->getStructNumElements();
+}
 
 //===----------------------------------------------------------------------===//
 //                         UndefValue Implementation
@@ -797,7 +805,14 @@ UndefValue *UndefValue::getElementValue(unsigned Idx) const {
   return getStructElement(Idx);
 }
 
-
+unsigned UndefValue::getNumElements() const {
+  const Type *Ty = getType();
+  if (const auto *AT = dyn_cast<ArrayType>(Ty))
+    return AT->getNumElements();
+  if (const auto *VT = dyn_cast<VectorType>(Ty))
+    return VT->getNumElements();
+  return Ty->getStructNumElements();
+}
 
 //===----------------------------------------------------------------------===//
 //                            ConstantXXX Classes