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

1 files changed, 17 insertions, 1 deletions

diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index 842590b24c..9849688023 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -133,6 +133,7 @@ public:
                                   CGF.getContext().typesAreCompatible(
                                     E->getArgType1(), E->getArgType2()));
   }
+  Value *VisitOffsetOfExpr(const OffsetOfExpr *E);
   Value *VisitSizeOfAlignOfExpr(const SizeOfAlignOfExpr *E);
   Value *VisitAddrLabelExpr(const AddrLabelExpr *E) {
     llvm::Value *V = CGF.GetAddrOfLabel(E->getLabel());
@@ -242,7 +243,7 @@ public:
     return Visit(E->getSubExpr());
   }
   Value *VisitUnaryOffsetOf(const UnaryOperator *E);
-
+    
   // C++
   Value *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
     return Visit(DAE->getExpr());
@@ -1030,6 +1031,21 @@ Value *ScalarExprEmitter::VisitUnaryLNot(const UnaryOperator *E) {
   return Builder.CreateZExt(BoolVal, ConvertType(E->getType()), "lnot.ext");
 }
 
+Value *ScalarExprEmitter::VisitOffsetOfExpr(const OffsetOfExpr *E) {
+  Expr::EvalResult Result;
+  if(E->Evaluate(Result, CGF.getContext()))
+    return llvm::ConstantInt::get(VMContext, Result.Val.getInt());
+  
+  // FIXME: Cannot support code generation for non-constant offsetof.
+  unsigned DiagID = CGF.CGM.getDiags().getCustomDiagID(Diagnostic::Error,
+                             "cannot compile non-constant __builtin_offsetof");
+  CGF.CGM.getDiags().Report(CGF.getContext().getFullLoc(E->getLocStart()), 
+                            DiagID)
+    << E->getSourceRange();
+  
+  return llvm::Constant::getNullValue(ConvertType(E->getType()));
+}
+
 /// VisitSizeOfAlignOfExpr - Return the size or alignment of the type of
 /// argument of the sizeof expression as an integer.
 Value *