Amazing that there are still issues with the fields of anonymous struct/unions..

Allow taking the address of such a field for a pointer-to-member constant. Fixes rdar://8818236.

llvm-svn: 124575

clang/include/clang/Sema/Sema.h

@@ -1784,6 +1784,7 @@ public:
                               const CXXScopeSpec *SS = 0);
   ExprResult
   BuildAnonymousStructUnionMemberReference(SourceLocation Loc,
+                                           const CXXScopeSpec &SS,
                                            IndirectFieldDecl *IndirectField,
                                            Expr *BaseObjectExpr = 0,
                                       SourceLocation OpLoc = SourceLocation());

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -493,17 +493,41 @@ ItaniumCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
                                    /*Packed=*/false);
 }
 
+static uint64_t getFieldOffset(const FieldDecl *FD, CodeGenModule &CGM) {
+  const CGRecordLayout &RL = CGM.getTypes().getCGRecordLayout(FD->getParent());
+  const llvm::StructType *ClassLTy = RL.getLLVMType();
+
+  unsigned FieldNo = RL.getLLVMFieldNo(FD);
+  return
+       CGM.getTargetData().getStructLayout(ClassLTy)->getElementOffset(FieldNo);
+}
+
 llvm::Constant *ItaniumCXXABI::EmitMemberPointer(const FieldDecl *FD) {
   // Itanium C++ ABI 2.3:
   //   A pointer to data member is an offset from the base address of
   //   the class object containing it, represented as a ptrdiff_t
 
-  const CGRecordLayout &RL = CGM.getTypes().getCGRecordLayout(FD->getParent());
-  const llvm::StructType *ClassLTy = RL.getLLVMType();
+  const RecordDecl *parent = FD->getParent();
+  if (!parent->isAnonymousStructOrUnion())
+    return llvm::ConstantInt::get(getPtrDiffTy(), getFieldOffset(FD, CGM));
 
-  unsigned FieldNo = RL.getLLVMFieldNo(FD);
-  uint64_t Offset = 
-    CGM.getTargetData().getStructLayout(ClassLTy)->getElementOffset(FieldNo);
+  // Handle a field injected from an anonymous struct or union.
+
+  assert(FD->getDeclName() && "Requested pointer to member with no name!");
+
+  // Find the record which the field was injected into.
+  while (parent->isAnonymousStructOrUnion())
+    parent = cast<RecordDecl>(parent->getParent());
+
+  RecordDecl::lookup_const_result lookup = parent->lookup(FD->getDeclName());
+  assert(lookup.first != lookup.second && "Didn't find the field!");
+  const IndirectFieldDecl *indirectFD = cast<IndirectFieldDecl>(*lookup.first);
+
+  uint64_t Offset = 0;
+  for (IndirectFieldDecl::chain_iterator
+         I= indirectFD->chain_begin(), E= indirectFD->chain_end(); I!=E; ++I) {
+    Offset += getFieldOffset(cast<FieldDecl>(*I), CGM);
+  }
 
   return llvm::ConstantInt::get(getPtrDiffTy(), Offset);
 }

clang/lib/Sema/SemaExpr.cpp

@@ -853,6 +853,7 @@ BuildFieldReferenceExpr(Sema &S, Expr *BaseExpr, bool IsArrow,
 
 ExprResult
 Sema::BuildAnonymousStructUnionMemberReference(SourceLocation Loc,
+                                               const CXXScopeSpec &SS,
                                             IndirectFieldDecl *IndirectField,
                                                Expr *BaseObjectExpr,
                                                SourceLocation OpLoc) {
@@ -911,9 +912,21 @@ Sema::BuildAnonymousStructUnionMemberReference(SourceLocation Loc,
       BaseQuals = Qualifiers::fromCVRMask(MD->getTypeQualifiers());
     }
 
-    if (!BaseObjectExpr)
-      return ExprError(Diag(Loc, diag::err_invalid_non_static_member_use)
-        << IndirectField->getDeclName());
+    if (!BaseObjectExpr) {
+      // The field is referenced for a pointer-to-member expression, e.g:
+      //
+      //   struct S {
+      //     union {
+      //       char c;
+      //     };
+      //   };
+      //   char S::*foo  = &S::c;
+      //
+      FieldDecl *field = IndirectField->getAnonField();
+      DeclarationNameInfo NameInfo(field->getDeclName(), Loc);
+      return BuildDeclRefExpr(field, field->getType().getNonReferenceType(),
+                              VK_LValue, NameInfo, &SS);
+    }
   }
 
   // Build the implicit member references to the field of the
@@ -929,9 +942,6 @@ Sema::BuildAnonymousStructUnionMemberReference(SourceLocation Loc,
   for (; FI != FEnd; FI++) {
     FieldDecl *Field = cast<FieldDecl>(*FI);
 
-    // FIXME: the first access can be qualified
-    CXXScopeSpec SS;
-
     // FIXME: these are somewhat meaningless
     DeclarationNameInfo MemberNameInfo(Field->getDeclName(), Loc);
     DeclAccessPair FoundDecl = DeclAccessPair::make(Field, Field->getAccess());
@@ -2035,7 +2045,7 @@ Sema::BuildImplicitMemberExpr(const CXXScopeSpec &SS,
   // FIXME: This needs to happen post-isImplicitMemberReference?
   // FIXME: template-ids inside anonymous structs?
   if (IndirectFieldDecl *FD = R.getAsSingle<IndirectFieldDecl>())
-    return BuildAnonymousStructUnionMemberReference(Loc, FD);
+    return BuildAnonymousStructUnionMemberReference(Loc, SS, FD);
 
 
   // If this is known to be an instance access, go ahead and build a
@@ -2228,7 +2238,7 @@ Sema::BuildDeclarationNameExpr(const CXXScopeSpec &SS,
 
   // Handle anonymous.
   if (IndirectFieldDecl *FD = dyn_cast<IndirectFieldDecl>(VD))
-    return BuildAnonymousStructUnionMemberReference(Loc, FD);
+    return BuildAnonymousStructUnionMemberReference(Loc, SS, FD);
 
   ExprValueKind VK = getValueKindForDecl(Context, VD);
 
@@ -3400,7 +3410,7 @@ Sema::BuildMemberReferenceExpr(Expr *BaseExpr, QualType BaseExprType,
   if (IndirectFieldDecl *FD = dyn_cast<IndirectFieldDecl>(MemberDecl))
     // We may have found a field within an anonymous union or struct
     // (C++ [class.union]).
-    return BuildAnonymousStructUnionMemberReference(MemberLoc, FD,
+    return BuildAnonymousStructUnionMemberReference(MemberLoc, SS, FD,
                                                     BaseExpr, OpLoc);
 
   if (VarDecl *Var = dyn_cast<VarDecl>(MemberDecl)) {
@@ -7346,6 +7356,8 @@ static QualType CheckAddressOfOperand(Sema &S, Expr *OrigOp,
             return QualType();
           }
 
+          while (cast<RecordDecl>(Ctx)->isAnonymousStructOrUnion())
+            Ctx = Ctx->getParent();
           return S.Context.getMemberPointerType(op->getType(),
                 S.Context.getTypeDeclType(cast<RecordDecl>(Ctx)).getTypePtr());
         }

clang/test/CodeGenCXX/anonymous-union-member-initializer.cpp

@@ -1,5 +1,19 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin10 -emit-llvm -o - %s | FileCheck %s
 
+// rdar://8818236
+namespace rdar8818236 {
+struct S {
+  char c2;
+  union {
+    char c;
+    int i;
+  };
+};
+
+// CHECK: @_ZN11rdar88182363fooE = global i64 4
+char S::*foo  = &S::c;
+}
+
 struct A {
   union {
     int a;