Fix PR19195

[karthikthecool]

Summary

Hi All,
A small patch ti fix PR19195. A call to getExpr from CXXDefaultInitExpr can return null in case we have not yet parsed and attached the in class initializer like in this test case.
Check if getExpr returns null and handle the same to prevent a crash during dynamic cast in StmtVisitor.
It would be great if someone could review the same and let me know if this is good for commit.

Thanks
Karthik Bhat

[karthikthecool]

ping..

Thanks
Karthik Bhat

[rsmith]

This doesn't look right to me. If the initializer hasn't been parsed by the time we get to IR generation for the default constructor, something has gone *very* badly wrong.

The right fix here is probably to implement the proposed resolution for CWG issue 1396 -- lazily instantiate default initializers for non-static data members as we do for default arguments.

[karthikthecool]

Abandon old review as im no longer working on the same.
Thanks

lib/CodeGen/CGDecl.cpp

 
 void CodeGenFunction::EmitScalarInit(const Expr *init,
                                      const ValueDecl *D,
                                      LValue lvalue,
                                      bool capturedByInit) {
   Qualifiers::ObjCLifetime lifetime = lvalue.getObjCLifetime();
   if (!lifetime) {
     llvm::Value *value = EmitScalarExpr(init);
+    if (!value)
+      return;
     if (capturedByInit)
       drillIntoBlockVariable(*this, lvalue, cast<VarDecl>(D));
     EmitStoreThroughLValue(RValue::get(value), lvalue, true);
     return;
   }
   
   if (const CXXDefaultInitExpr *DIE = dyn_cast<CXXDefaultInitExpr>(init))
     init = DIE->getExpr();

lib/CodeGen/CGExprScalar.cpp

Value *VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *E) {
     return EmitLoadOfLValue(E);
   }
 
   Value *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
     return Visit(DAE->getExpr());
   }
   Value *VisitCXXDefaultInitExpr(CXXDefaultInitExpr *DIE) {
     CodeGenFunction::CXXDefaultInitExprScope Scope(CGF);
+    if(!DIE->getExpr())
+      return 0;
     return Visit(DIE->getExpr());
   }
   Value *VisitCXXThisExpr(CXXThisExpr *TE) {
     return CGF.LoadCXXThis();
   }
 
   Value *VisitExprWithCleanups(ExprWithCleanups *E) {
     CGF.enterFullExpression(E);

test/CodeGenCXX/pr19195.cpp

+// RUN: %clang_cc1 -std=c++11 -emit-llvm-only %s -o %t
+/* Testcase for PR19195 - clang hits assert during in class initialization */
+
+class Cls {
+  Cls();
+  template <typename> struct Templ {
+    Templ() {}
+    int initialized_member = 0;
+  };
+  Templ<int> trigger_instantiation;
+};
+Cls::Cls() {}