Add a getAlignOf helper for getting the ABI alignment of a

type as a target independent constant expression.  I confess
that I didn't check that this method works as intended (though
I did test the equivalent hand-written IR a little).  But what
could possibly go wrong!

llvm-svn: 72213

2 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/VMCore/Constants.cpp b/llvm/lib/VMCore/Constants.cpp
index b38474d28a4..d3f9b7f45b7 100644
--- a/llvm/lib/VMCore/Constants.cpp
+++ b/llvm/lib/VMCore/Constants.cpp
@@ -2082,6 +2082,17 @@ Constant *ConstantExpr::getBitCast(Constant *C, const Type *DstTy) {
   return getFoldedCast(Instruction::BitCast, C, DstTy);
 }
 
+Constant *ConstantExpr::getAlignOf(const Type *Ty) {
+  // alignof is implemented as: (i64) gep ({i8,Ty}*)null, 0, 1
+  const Type *AligningTy = StructType::get(Type::Int8Ty, Ty, NULL);
+  Constant *NullPtr = getNullValue(AligningTy->getPointerTo());
+  Constant *Zero = ConstantInt::get(Type::Int32Ty, 0);
+  Constant *One = ConstantInt::get(Type::Int32Ty, 1);
+  Constant *Indices[2] = { Zero, One };
+  Constant *GEP = getGetElementPtr(NullPtr, Indices, 2);
+  return getCast(Instruction::PtrToInt, GEP, Type::Int32Ty);
+}
+
 Constant *ConstantExpr::getSizeOf(const Type *Ty) {
   // sizeof is implemented as: (i64) gep (Ty*)null, 1
   Constant *GEPIdx = ConstantInt::get(Type::Int32Ty, 1);
diff --git a/llvm/lib/VMCore/Core.cpp b/llvm/lib/VMCore/Core.cpp
index 1fa83ebd1c0..f85dbe76119 100644
--- a/llvm/lib/VMCore/Core.cpp
+++ b/llvm/lib/VMCore/Core.cpp
@@ -356,6 +356,10 @@ LLVMValueRef LLVMConstVector(LLVMValueRef *ScalarConstantVals, unsigned Size) {
 
 /*--.. Constant expressions ................................................--*/
 
+LLVMValueRef LLVMAlignOf(LLVMTypeRef Ty) {
+  return wrap(ConstantExpr::getAlignOf(unwrap(Ty)));
+}
+
 LLVMValueRef LLVMSizeOf(LLVMTypeRef Ty) {
   return wrap(ConstantExpr::getSizeOf(unwrap(Ty)));
 }