[Bug c++/82326] New: static_cast for vector extension not working?

[gcc-bugs at marehr dot dialup.fu-berlin.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82326

            Bug ID: 82326
           Summary: static_cast for vector extension not working?
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc-bugs at marehr dot dialup.fu-berlin.de
  Target Milestone: ---

My problem is the following:

```
// main.cpp
#include <cstdint>
#include <x86intrin.h>

using int32x4_t = int32_t __attribute__ ((__vector_size__(16)));
using uint32x4_t = uint32_t __attribute__ ((__vector_size__(16)));

int main()
{
    int32x4_t a{-1, 0, 1, 2};

    // invalid static_cast from type ‘int32x4_t {aka __vector(4) int}’
    // to type ‘uint32x4_t {aka __vector(4) unsigned int}
    uint32x4_t b = static_cast<uint32x4_t>(a); // fails with above message

    uint32x4_t c = reinterpret_cast<uint32x4_t>(a); // works

    // invalid static_cast from type ‘int32x4_t {aka __vector(4) int}’
    // to type ‘__m128i {aka __vector(2) long long int}
    __m128i d = static_cast<__m128i>(a); // fails with above message

    __m128i e = reinterpret_cast<__m128i>(a); // works
    return 0;
}
```

> g++ -msse4 main.cpp -o main


Why is a static_cast not working?

This is a hassle, because different compilers support different syntaxes. 

* gcc allows only reinterpret_cast and C-style casts
* clang allows both static_cast and reinterpret_cast and C-style casts
* icc (Intel Compiler) allows only static_cast and C-style casts

Thank you!