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, 45 insertions, 0 deletions

diff --git a/lib/Frontend/PCHReaderStmt.cpp b/lib/Frontend/PCHReaderStmt.cpp
index 5e08be138a..8588c8aa1a 100644
--- a/lib/Frontend/PCHReaderStmt.cpp
+++ b/lib/Frontend/PCHReaderStmt.cpp
@@ -71,6 +71,7 @@ namespace {
     unsigned VisitCharacterLiteral(CharacterLiteral *E);
     unsigned VisitParenExpr(ParenExpr *E);
     unsigned VisitUnaryOperator(UnaryOperator *E);
+    unsigned VisitOffsetOfExpr(OffsetOfExpr *E);
     unsigned VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *E);
     unsigned VisitArraySubscriptExpr(ArraySubscriptExpr *E);
     unsigned VisitCallExpr(CallExpr *E);
@@ -432,6 +433,44 @@ unsigned PCHStmtReader::VisitUnaryOperator(UnaryOperator *E) {
   return 1;
 }
 
+unsigned PCHStmtReader::VisitOffsetOfExpr(OffsetOfExpr *E) {
+  typedef OffsetOfExpr::OffsetOfNode Node;
+  VisitExpr(E);
+  assert(E->getNumComponents() == Record[Idx]);
+  ++Idx;
+  assert(E->getNumExpressions() == Record[Idx]);
+  ++Idx;
+  E->setOperatorLoc(SourceLocation::getFromRawEncoding(Record[Idx++]));
+  E->setRParenLoc(SourceLocation::getFromRawEncoding(Record[Idx++]));
+  E->setTypeSourceInfo(Reader.GetTypeSourceInfo(Record, Idx));
+  for (unsigned I = 0, N = E->getNumComponents(); I != N; ++I) {
+    Node::Kind Kind = static_cast<Node::Kind>(Record[Idx++]);
+    SourceLocation Start = SourceLocation::getFromRawEncoding(Record[Idx++]);
+    SourceLocation End = SourceLocation::getFromRawEncoding(Record[Idx++]);
+    switch (Kind) {
+    case Node::Array:
+      E->setComponent(I, Node(Start, Record[Idx++], End));
+      break;
+        
+    case Node::Field:
+      E->setComponent(I, 
+             Node(Start,  
+                  dyn_cast_or_null<FieldDecl>(Reader.GetDecl(Record[Idx++])),
+                  End));
+      break;
+
+    case Node::Identifier:
+      E->setComponent(I, Node(Start, Reader.GetIdentifier(Record[Idx++]), End));
+      break;
+    }
+  }
+  
+  for (unsigned I = 0, N = E->getNumExpressions(); I != N; ++I)
+    E->setIndexExpr(I, cast_or_null<Expr>(StmtStack[StmtStack.size() - N + I]));
+  
+  return E->getNumExpressions();
+}
+
 unsigned PCHStmtReader::VisitSizeOfAlignOfExpr(SizeOfAlignOfExpr *E) {
   VisitExpr(E);
   E->setSizeof(Record[Idx++]);
@@ -1105,6 +1144,12 @@ Stmt *PCHReader::ReadStmt(llvm::BitstreamCursor &Cursor) {
       S = new (Context) UnaryOperator(Empty);
       break;
 
+    case pch::EXPR_OFFSETOF:
+      S = OffsetOfExpr::CreateEmpty(*Context, 
+                                    Record[PCHStmtReader::NumExprFields],
+                                    Record[PCHStmtReader::NumExprFields + 1]);
+      break;
+        
     case pch::EXPR_SIZEOF_ALIGN_OF:
       S = new (Context) SizeOfAlignOfExpr(Empty);
       break;