add a new "getPreferredTypeAlign" method to return the preferred alignment

of a type.  The implementation is currently something of a hack, but is 
sufficient for now and allows clients to be built on it.

llvm-svn: 63108

1 files changed, 16 insertions, 0 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 2662860af2f..e7c08e2da39 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -453,6 +453,22 @@ ASTContext::getTypeInfo(const Type *T) {
   return std::make_pair(Width, Align);
 }
 
+/// getPreferredTypeAlign - Return the "preferred" alignment of the specified
+/// type for the current target in bits.  This can be different than the ABI
+/// alignment in cases where it is beneficial for performance to overalign
+/// a data type.
+unsigned ASTContext::getPreferredTypeAlign(const Type *T) {
+  unsigned ABIAlign = getTypeAlign(T);
+  
+  // Doubles should be naturally aligned if possible.
+  if (const BuiltinType *BT = dyn_cast<BuiltinType>(getCanonicalType(T)))
+    if (BT->getKind() == BuiltinType::Double)
+      return std::max(ABIAlign, 8U);
+  
+  return ABIAlign;
+}
+
+
 /// LayoutField - Field layout.
 void ASTRecordLayout::LayoutField(const FieldDecl *FD, unsigned FieldNo,
                                   bool IsUnion, unsigned StructPacking,