Completely reimplement __builtin_offsetof, based on a patch by Roberto

Amadini.

This change introduces a new expression node type, OffsetOfExpr, that
describes __builtin_offsetof. Previously, __builtin_offsetof was
implemented using a unary operator whose subexpression involved
various synthesized array-subscript and member-reference expressions,
which was ugly and made it very hard to instantiate as a
template. OffsetOfExpr represents the AST more faithfully, with proper
type source information and a more compact representation.

OffsetOfExpr also has support for dependent __builtin_offsetof
expressions; it can be value-dependent, but will never be
type-dependent (like sizeof or alignof). This commit introduces
template instantiation for __builtin_offsetof as well.

There are two major caveats to this patch:

  1) CodeGen cannot handle the case where __builtin_offsetof is not a
  constant expression, so it produces an error. So, to avoid
  regressing in C, we retain the old UnaryOperator-based
  __builtin_offsetof implementation in C while using the shiny new
  OffsetOfExpr implementation in C++. The old implementation can go
  away once we have proper CodeGen support for this case, which we
  expect won't cause much trouble in C++.

  2) __builtin_offsetof doesn't work well with non-POD class types,
  particularly when the designated field is found within a base
  class. I will address this in a subsequent patch.

Fixes PR5880 and a bunch of assertions when building Boost.Python
tests. 

llvm-svn: 102542

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/Frontend/StmtXML.cpp b/clang/lib/Frontend/StmtXML.cpp
index ce474d36539..21dc0ba0a18 100644
--- a/clang/lib/Frontend/StmtXML.cpp
+++ b/clang/lib/Frontend/StmtXML.cpp
@@ -125,6 +125,7 @@ namespace  {
     void VisitFloatingLiteral(FloatingLiteral *Node);
     void VisitStringLiteral(StringLiteral *Str);
     void VisitUnaryOperator(UnaryOperator *Node);
+    void VisitOffsetOfExpr(OffsetOfExpr *Node);
     void VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *Node);
     void VisitMemberExpr(MemberExpr *Node);
     void VisitExtVectorElementExpr(ExtVectorElementExpr *Node);
@@ -308,6 +309,10 @@ void StmtXML::VisitUnaryOperator(UnaryOperator *Node) {
   Doc.addAttribute("op_code", getOpcodeStr(Node->getOpcode()));
 }
 
+void StmtXML::OffsetOfExpr(OffsetOfExpr *Node) {
+  DumpExpr(Node);
+}
+
 void StmtXML::VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *Node) {
   DumpExpr(Node);
   Doc.addAttribute("is_sizeof", Node->isSizeOf() ? "sizeof" : "alignof");