[llvm-bugs] [Bug 48070] New: User-defined float literal broken with device nvptx64-nvidia-

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48070

            Bug ID: 48070
           Summary: User-defined float literal broken with device
                    nvptx64-nvidia-
           Product: clang
           Version: 11.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: OpenMP
          Assignee: unassignedclangbugs at nondot.org
          Reporter: gcc.j.kelling at hzdr.de
                CC: llvm-bugs at lists.llvm.org

Created attachment 24132
  --> https://bugs.llvm.org/attachment.cgi?id=24132&action=edit
minimal reproducer

The attached example, defining a user-defined float literal type and using it
in an OpenMP target region is valid and compiles for x86_64, using
```
clang++  -fopenmp -fopenmp=libomp -fopenmp-targets=x86_64-pc-linux-gnu
literal.cpp
```

It does does not compile with
```
clang++  -fopenmp -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda
literal.cpp 
```
failing with the message:
```
../literal/literal.cpp:14:11: error: 'operator""_X' requires 128 bit size 'long
double' type support, but device 'nvptx64-nvidia-cuda' does not support it
                        a += 1._X;
                               ^
../literal/literal.cpp:1:18: note: 'operator""_X' defined here
constexpr double operator"" _X (long double a)
                 ^
```

Expected behavior: The long double argument type of the literal operator is a
literal and does live at runtime, only the return value enters runtime as a
constant, thus device support for long double by the target architecture is not
needed.

Also note, that such literals for floats can only be defined using long double,
raising the following error when, e.g., using double instead:
```
literal.cpp:1:33: error: invalid literal operator parameter type 'double', did
you mean 'long double'?
constexpr double operator"" _X (double a)
                                ^~~~~~~~
```
Thus, allowing target architecture restriction enter compile time here, would
make support for user-defined literals in target regions impossible.

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