Calculate offset correctly when taking the address of a virtual member function.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95305 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 10 insertions, 3 deletions

diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index cb6e1d8140..928cb616b2 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -327,7 +327,11 @@ void AggExprEmitter::VisitUnaryAddrOf(const UnaryOperator *E) {
     int64_t Index = 
       CGF.CGM.getVtableInfo().getMethodVtableIndex(MD);
     
-    FuncPtr = llvm::ConstantInt::get(PtrDiffTy, Index + 1);
+    // Itanium C++ ABI 2.3:
+    //   For a non-virtual function, this field is a simple function pointer. 
+    //   For a virtual function, it is 1 plus the virtual table offset 
+    //   (in bytes) of the function, represented as a ptrdiff_t. 
+    FuncPtr = llvm::ConstantInt::get(PtrDiffTy, (Index * 8) + 1);
   } else {
     FuncPtr = llvm::ConstantExpr::getPtrToInt(CGF.CGM.GetAddrOfFunction(MD), 
                                               PtrDiffTy);
diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index 81209da6c6..a358b54fa3 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -418,8 +418,11 @@ public:
     // Get the function pointer (or index if this is a virtual function).
     if (MD->isVirtual()) {
       uint64_t Index = CGM.getVtableInfo().getMethodVtableIndex(MD);
-      
-      // The pointer is 1 + the virtual table offset in bytes.
+
+      // Itanium C++ ABI 2.3:
+      //   For a non-virtual function, this field is a simple function pointer. 
+      //   For a virtual function, it is 1 plus the virtual table offset 
+      //   (in bytes) of the function, represented as a ptrdiff_t. 
       Values[0] = llvm::ConstantInt::get(PtrDiffTy, (Index * 8) + 1);
     } else {
       llvm::Constant *FuncPtr = CGM.GetAddrOfFunction(MD);