[PATCH] D53764: [OpenCL] Enable address spaces for references in C++

[Anastasia Stulova via Phabricator via cfe-commits]

Anastasia added inline comments.


================
Comment at: lib/Sema/SemaExprCXX.cpp:4289
+                             /*BasePath=*/nullptr, CCK)
+               .get();
 
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rjmccall wrote:
> Anastasia wrote:
> > rjmccall wrote:
> > > Okay.  But if `ToType` *isn't* a reference type, this will never be an address-space conversion.  I feel like this code could be written more clearly to express what it's trying to do.
> > I hope it makes more sense now. Btw, it also applies to pointer type.
> The logic is wrong for pointer types; if you're converting pointers, you need to be checking the address space of the pointee type of the from type.
> 
> It sounds like this is totally inadequately tested; please flesh out the test with all of these cases.  While you're at it, please ensure that there are tests verifying that we don't allowing address-space changes in nested positions.
Thanks for spotting this bug! The generated IR for the test was still correct because AS of `FromType` happened to correctly mismatch AS of pointee of `ToType`.

I failed to construct the test case where it would miss classifying `addrspacecast` due to OpenCL or C++ sema rules but I managed to add a case in which `addrspacecast` was incorrectly added for pointers where it wasn't needed (see line 36 of the test). I think this code is covered now.

As for the address space position in pointers, the following test checks the address spaces of pointers in `addrspacecast`. For the other program paths we also have a test with similar checks in `test/CodeGenOpenCL/address-spaces-conversions.cl` that we now run for C++ mode too.

BTW, while trying to construct a test case for the bug, I have discovered that multiple pointer indirection casting isn't working correctly. I.e. for the following program:
  kernel void foo(){
     __private int** loc;
     int** loc_p = loc;
     **loc_p = 1;
  }
We generate:
  bitcast i32* addrspace(4)* %0 to i32 addrspace(4)* addrspace(4)*
in OpenCL C and then perform `store` over pointer in AS 4 (generic). We have now lost the information that the original pointer was in `private` AS and that the adjustment of AS segment has to be performed before accessing memory pointed by the pointer. Based on the current specification of `addrspacecast` in https://llvm.org/docs/LangRef.html#addrspacecast-to-instruction I am not very clear whether it can be used for this case without any modifications or clarifications and also what would happen if there are multiple AS mismatches. I am going to look at this issue separately in more details. In OpenCL C++ an ICE is triggered for this though. Let me know if you have any thoughts on this.


https://reviews.llvm.org/D53764