[SemaCXX] Fix handling of C-style casts from void pointers to pointers in different address space.

[mjacob]

Summary

When for example handling C-style casts from void * to `int
attribute((address_space(1))) *` in C++ code, Sema previously set the cast
kind to CK_BitCast incorrectly, which caused an assert to fail in CodeGen. This
patch changes Sema to set the cast kind to CK_AddressSpaceConversion if source
and destination point to different address spaces.

[rsmith]

lib/Sema/SemaCast.cpp

1081–1083

I would expect to get both a CK_BitCast *and* a CK_AddressSpaceCast created for this case. Note that by not returning CK_BitCast, you lose the checkCastAlign call in the caller.

Instead, can you push this check down into wherever we're building the conversion, so that if we try to create a CK_BitCast that crosses address spaces, we additionally create a CK_AddressSpaceCast?

[mjacob]

lib/Sema/SemaCast.cpp

1081–1083

I'm not sure what you mean by "additionally create a CK_AddressSpaceCast". Please clarify.

Would it also be possible to extend all places which call checkCastAlign() to also call it for CK_AddressSpaceCast?

lib/Sema/SemaCast.cpp

if (SrcPointee->isVoidType()) {
             SrcPointeeQuals.removeObjCGCAttr();
             SrcPointeeQuals.removeObjCLifetime();
             if (DestPointeeQuals != SrcPointeeQuals &&
                 !DestPointeeQuals.compatiblyIncludes(SrcPointeeQuals)) {
               msg = diag::err_bad_cxx_cast_qualifiers_away;
               return TC_Failed;
             }
           }
-          Kind = CK_BitCast;
+          unsigned SrcAS = SrcPointee.getAddressSpace();
+          unsigned DestAS = DestPointee.getAddressSpace();
+          Kind = SrcAS != DestAS ? CK_AddressSpaceConversion : CK_BitCast;
           return TC_Success;
         }
 
         // Microsoft permits static_cast from 'pointer-to-void' to
         // 'pointer-to-function'.
         if (!CStyle && Self.getLangOpts().MSVCCompat &&
             DestPointee->isFunctionType()) {
           Self.Diag(OpRange.getBegin(), diag::ext_ms_cast_fn_obj) << OpRange;

test/CodeGenCXX/address-space-cast.cpp

+// RUN: %clang_cc1 -emit-llvm -o - %s
+
+typedef void *void_ptr;
+typedef int __attribute__((address_space(1))) *int_ptr_1;
+
+void test_cstyle_cast_from_void_ptr(void_ptr vp) {
+  (void)(int_ptr_1)(vp);
+}