[llvm-bugs] [Bug 32662] New: Address space 8388355 should not be generic in C++

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http://bugs.llvm.org/show_bug.cgi?id=32662

            Bug ID: 32662
           Summary: Address space 8388355 should not be generic in C++
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: pkeir at outlook.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 18286
  --> http://bugs.llvm.org/attachment.cgi?id=18286&action=edit
A MWE similar to the example described

LLVM supports address space annotation such as:

__attribute__((address_space(42))) int *p;

A most useful aspect of their functionality is knowing that such pointers
cannot be converted to one another. For example, this static assert passes:

using pt1 = __attribute__((address_space(1))) int *;
using pt2 = __attribute__((address_space(2))) int *;
static_assert(!std::is_convertible<pt0,pt1>::value,"");

Though this functionality has many uses within standard C++, LLVM's OpenCL
implementation also uses this feature. Since around Clang 3.9, however, an
aspect particular to OpenCL appears when compiling C++. This aspect should
rather rely on the user specifying explicitly that OpenCL is to be compiled;
perhaps via "-x cl -cl-std=CL2.0".

Address space 8388355 is used by Clang to implement the generic address space
added in OpenCL 2.0. In C++, converting a pointer targeting address space
8388355 should behave the same as pointers targeting other address spaces: it
should not be convertible.

As a concrete example, the following should not produce an error, but as of
Clang 3.9 it does:

using pt1       = __attribute__((address_space(1)))       int *;
using pt2       = __attribute__((address_space(2)))       int *;
using pt8388355 = __attribute__((address_space(8388355))) int *;
static_assert(!std::is_convertible<pt0,pt8388355>::value,"");
static_assert(!std::is_convertible<pt1,pt8388355>::value,"");

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