[PATCH] D102689: [C++4OpenCL] Allow address space conversion in reinterpret_cast

[John McCall via Phabricator via cfe-commits]

rjmccall added a reviewer: rsmith.
rjmccall added a comment.

Top-level qualifiers aren't normally meaningful on pr-values.

The C standard says that casts are to the unqualified type:

  N2454 6.5.4p5: Preceding an expression by a parenthesized type name converts the value of the expression to the unqualified version of the named type.

The C++ standard does not appear to have similar wording.  On the other hand, the C++ standard says that e.g. "The result of the expression `(T) cast-expression` is of type `T`", and similarly for the other casts, which is clearly just wrong if `T` is a reference type; the wording clarifies that the expression is an l-value or x-value if the type is a reference but doesn't remove the reference-ness of the expression type as it must, unless that's done by some other clause at a distance.  CC'ing Richard.

It makes sense to me that qualifiers on the cast type ought to be uniformly and silently ignored, including address space qualifiers.  C++ has a very strange feature of allowing qualifiers on class types in particular circumstances, so we might need to be permissive about that, although that's tricky for address spaces because (unlike with `const` or `volatile`) we cannot in fact allocate a temporary in an arbitrary address space.

I agree that this should be done uniformly, not just in OpenCL, unless OpenCL wants rules that differ from what we think they ought to be in general.


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D102689