Fix crash in codegen on casting to `bool &`.

[ABataev]

Summary

Currently codegen crashes trying to emit casting to bool &. It happens because bool type is converted to i1 and later then lvalue for reference is converted to i1*. But when codegen tries to load this lvalue it crashes trying to load value from this i1*.

[rjmccall]

LGTM.

cfe/trunk/lib/CodeGen/CGExprScalar.cpp

Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
   switch (Kind) {
   case CK_Dependent: llvm_unreachable("dependent cast kind in IR gen!");
   case CK_BuiltinFnToFnPtr:
     llvm_unreachable("builtin functions are handled elsewhere");
 
   case CK_LValueBitCast:
   case CK_ObjCObjectLValueCast: {
     Address Addr = EmitLValue(E).getAddress();
-    Addr = Builder.CreateElementBitCast(Addr, ConvertType(DestTy));
+    Addr = Builder.CreateElementBitCast(Addr, CGF.ConvertTypeForMem(DestTy));
     LValue LV = CGF.MakeAddrLValue(Addr, DestTy);
     return EmitLoadOfLValue(LV, CE->getExprLoc());
   }
 
   case CK_CPointerToObjCPointerCast:
   case CK_BlockPointerToObjCPointerCast:
   case CK_AnyPointerToBlockPointerCast:
   case CK_BitCast: {

cfe/trunk/test/CodeGenCXX/cast-to-ref-bool.cpp

+// RUN: %clang_cc1 -triple x86_64-apple-darwin -emit-llvm -o - %s | FileCheck %s
+
+// CHECK-LABEL: main
+int main(int argc, char **argv) {
+  // CHECK: load i8, i8* %
+  // CHECK-NEXT: trunc i8 %{{.+}} to i1
+  bool b = (bool &)argv[argc][1];
+  return b;
+}