Add a comment about the "getelementptr null" trick.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77262 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/VMCore/LLVMContext.cpp b/lib/VMCore/LLVMContext.cpp
index d7f4594e3ab4e860137c20022be6ed2a692c7b37..722e29ee5dca0fce83805451207e4206ab531ad2 100644 (file)
--- a/lib/VMCore/LLVMContext.cpp
+++ b/lib/VMCore/LLVMContext.cpp
@@ -419,6 +419,7 @@ Constant* LLVMContext::getConstantExprInsertValue(Constant* Agg, Constant* Val,
 
 Constant* LLVMContext::getConstantExprSizeOf(const Type* Ty) {
   // sizeof is implemented as: (i64) gep (Ty*)null, 1
+  // Note that a non-inbounds gep is used, as null isn't within any object.
   Constant *GEPIdx = ConstantInt::get(Type::Int32Ty, 1);
   Constant *GEP = getConstantExprGetElementPtr(
                             getNullValue(getPointerTypeUnqual(Ty)), &GEPIdx, 1);