[Bug target/115054] New: __float128 and _Float16 use incorrect ABI on x86-64 MinGW

["tmgross at umich dot edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054

            Bug ID: 115054
           Summary: __float128 and _Float16 use incorrect ABI on x86-64
                    MinGW
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tmgross at umich dot edu
  Target Milestone: ---

GCC appears to try to pass half and quad-precision floating point numbers
(_Float16 and __float128) using the integer calling convention on x86-64 MinGW.
They should get passed with the floating point CC in SSE registers, like other
floats, as is done by GCC x86-64 linux, Clang x86-64 linux, and Clang x86-64
MinGW.

Sample:

    void f16_ext(_Float16);
    void f16_entry(float _, _Float16 a) {
        asm("nop # marker");
        f16_ext(a);
    }

    void f32_ext(float);
    void f32_entry(float _, float a) {
        asm("nop # marker");
        f32_ext(a);
    }

    void f64_ext(double);
    void f64_entry(float _, double a) {
        asm("nop # marker");
        f64_ext(a);
    }

    void f128_ext(__float128);
    void f128_entry(float _, __float128 a) {
        asm("nop # marker");
        f128_ext(a);
    }

Incorrect output from GCC on x64 MinGW (O2):

    f16_entry:
        mov     ecx, edx
        nop # marker
        jmp     f16_ext
    f32_entry:
        movaps  xmm0, xmm1
        nop # marker
        jmp     f32_ext
    f64_entry:
        movapd  xmm0, xmm1
        nop # marker
        jmp     f64_ext
    f128_entry:
        sub     rsp, 56
        movdqa  xmm0, XMMWORD PTR [rdx]
        nop # marker
        lea     rcx, 32[rsp]
        movaps  XMMWORD PTR 32[rsp], xmm0
        call    f128_ext
        nop
        add     rsp, 56
        ret

Correct output from GCC on x64 Linux (O2):

    f16_entry:
        movaps  xmm0, xmm1
        nop # marker
        jmp     f16_ext
    f32_entry:
        movaps  xmm0, xmm1
        nop # marker
        jmp     f32_ext
    f64_entry:
        movapd  xmm0, xmm1
        nop # marker
        jmp     f64_ext
    f128_entry:
        movdqa  xmm0, xmm1
        nop # marker
        jmp     f128_ext

Correct output from Clang on both x64 Linux and x64 MinGW:

    f16_entry:                              # @f16_entry
        movaps  xmm0, xmm1
        nop     # marker
        jmp     f16_ext                         # TAILCALL
    f32_entry:                              # @f32_entry
        movaps  xmm0, xmm1
        nop     # marker
        jmp     f32_ext                         # TAILCALL
    f64_entry:                              # @f64_entry
        movaps  xmm0, xmm1
        nop     # marker
        jmp     f64_ext                         # TAILCALL
    f128_entry:                             # @f128_entry
        movaps  xmm0, xmm1
        nop     # marker
        jmp     f128_ext                        # TAILCALL


Tested with GCC 13.1. Link: https://gcc.godbolt.org/z/hdojahes5