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. 



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102542 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/StmtPrinter.cpp b/lib/AST/StmtPrinter.cpp
index 3996528..b50bb0c 100644
--- a/lib/AST/StmtPrinter.cpp
+++ b/lib/AST/StmtPrinter.cpp
@@ -17,6 +17,7 @@
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "llvm/Support/Format.h"
+#include "clang/AST/Expr.h"
 using namespace clang;
 
 //===----------------------------------------------------------------------===//
@@ -703,6 +704,35 @@
   OS << ")";
 }
 
+void StmtPrinter::VisitOffsetOfExpr(OffsetOfExpr *Node) {
+  OS << "__builtin_offsetof(";
+  OS << Node->getTypeSourceInfo()->getType().getAsString() << ", ";
+  bool PrintedSomething = false;
+  for (unsigned i = 0, n = Node->getNumComponents(); i < n; ++i) {
+    OffsetOfExpr::OffsetOfNode ON = Node->getComponent(i);
+    if (ON.getKind() == OffsetOfExpr::OffsetOfNode::Array) {
+      // Array node
+      OS << "[";
+      PrintExpr(Node->getIndexExpr(ON.getArrayExprIndex()));
+      OS << "]";
+      PrintedSomething = true;
+      continue;
+    }
+     
+    // Field or identifier node.
+    IdentifierInfo *Id = ON.getFieldName();
+    if (!Id)
+      continue;
+    
+    if (PrintedSomething)
+      OS << ".";
+    else
+      PrintedSomething = true;
+    OS << Id->getName();    
+  }
+  OS << ")";
+}
+
 void StmtPrinter::VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *Node) {
   OS << (Node->isSizeOf() ? "sizeof" : "__alignof");
   if (Node->isArgumentType())