[PCH] Make sure that the SourceExpr of a OpaqueValueExpr is always initialized
when deserialized, fixing random crashes in libclang.

Also simplifies how OpaqueValueExprs are [de]serialized.
The reader/writer automatically retains pointer equality of sub-statements (when a
statement node is referenced in multiple nodes), so no need to manually handle it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@145752 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Serialization/ASTWriterStmt.cpp b/lib/Serialization/ASTWriterStmt.cpp
index e3311e9..9f976f4 100644
--- a/lib/Serialization/ASTWriterStmt.cpp
+++ b/lib/Serialization/ASTWriterStmt.cpp
@@ -750,8 +750,6 @@
   for (PseudoObjectExpr::semantics_iterator
          i = E->semantics_begin(), e = E->semantics_end(); i != e; ++i) {
     Writer.AddStmt(*i);
-    if (OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(*i))
-      Writer.AddStmt(OVE->getSourceExpr());
   }
 
   Code = serialization::EXPR_PSEUDO_OBJECT;
@@ -1381,7 +1379,7 @@
 
 void ASTStmtWriter::VisitOpaqueValueExpr(OpaqueValueExpr *E) {
   VisitExpr(E);
-  Record.push_back(Writer.getOpaqueValueID(E));
+  Writer.AddStmt(E->getSourceExpr());
   Writer.AddSourceLocation(E->getLocation(), Record);
   Code = serialization::EXPR_OPAQUE_VALUE;
 }
@@ -1468,12 +1466,6 @@
   SwitchCaseIDs.clear();
 }
 
-unsigned ASTWriter::getOpaqueValueID(OpaqueValueExpr *e) {
-  unsigned &entry = OpaqueValues[e];
-  if (!entry) entry = OpaqueValues.size();
-  return entry;
-}
-
 /// \brief Write the given substatement or subexpression to the
 /// bitstream.
 void ASTWriter::WriteSubStmt(Stmt *S,