[PATCH] Fix adress cast for C++ in SEMA

[Samuel Antao]

================
Comment at: lib/Sema/Sema.cpp:339
@@ -338,3 +338,3 @@
 ExprResult Sema::ImpCastExprToType(Expr *E, QualType Ty,
                                    CastKind Kind, ExprValueKind VK,
                                    const CXXCastPath *BasePath,
----------------
rsmith wrote:
> sfantao wrote:
> > rsmith wrote:
> > > Why is `Kind` == `CK_NoOp` being passed in here for an address space cast? That seems like it might be a bug in the caller. Do you know which calls to `ImpCastExprToType` result in this happening?
> > This is the stack I have when I reach the point where the address cast is performed.
> > 
> > ```
> > clang::Sema::ImpCastExprToType() at Sema.cpp:370 0x141629b8	
> > clang::Sema::PerformImplicitConversion() at SemaExprCXX.cpp:3,447 0x1456981c	
> > clang::Sema::PerformImplicitConversion() at SemaExprCXX.cpp:2,964 0x14567124	
> > clang::InitializationSequence::Perform() at SemaInit.cpp:6,315 0x1465e444	
> > TryStaticImplicitCast() at SemaCast.cpp:1,522 0x141bb004	
> > TryStaticCast() at SemaCast.cpp:988 0x141b9e98	
> > (anonymous namespace)::CastOperation::CheckCXXCStyleCast at SemaCast.cpp:2,130 0x141b4248	
> > clang::Sema::BuildCStyleCastExpr() at SemaCast.cpp:2,455 0x141b3b60	
> > clang::Sema::ActOnCastExpr() at SemaExpr.cpp:5,545 0x144533a8	
> > ```
> > 
> > I see CK_NoOp is hardcoded in the caller:
> > 
> > ```
> >   case ICK_Qualification: {
> >     // The qualification keeps the category of the inner expression, unless the
> >     // target type isn't a reference.
> >     ExprValueKind VK = ToType->isReferenceType() ?
> >                                   From->getValueKind() : VK_RValue;
> >     From = ImpCastExprToType(From, ToType.getNonLValueExprType(Context),
> >                              CK_NoOp, VK, /*BasePath=*/nullptr, CCK).get();
> > ```
> > Should I fix something in here?
> > 
> If that's the only code path through which we get this wrong, my preference would be to move the fix into `PerformImplicitConversion`, and add an assert to `ImpCastExprToType` that we're not changing the address space with a `CK_NoOp` cast.
I was comparing what was going on for C and C++ and I see that for C the address cast is identified right away in CheckCStyleCast in: 
```
  Kind = Self.PrepareScalarCast(SrcExpr, DestType);
```
Therefore I thought it would make sense to do the same for C++ in  CheckCXXCStyleCast. I added the assertion in the place you suggested anyway. 

I understand this is not exactly what you requested but it looks as a more clean fix. If you do not agree, let me know and I can switch back to what you were originally proposing.

================
Comment at: test/Sema/address-space-cast.c:1
@@ +1,2 @@
+// RUN: %clang_cc1 -emit-llvm -o - -x c %s | FileCheck -check-prefix=CHECK %s
+// RUN: %clang_cc1 -emit-llvm -o - -x c++ %s | FileCheck -check-prefix=CHECK-CXX %s
----------------
rsmith wrote:
> Please move this test to test/CodeGen (I know, you're testing a Sema change, but the primary impact of your change is to make us emit the right IR, and that's what you're testing.)
Done!

http://reviews.llvm.org/D7606

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