[Issue 21474] ICE with core.simd and -O ("Illegal Instruction")

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21474

mhh <maxhaton at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxhaton at gmail.com

--- Comment #3 from mhh <maxhaton at gmail.com> ---
(In reply to ponce from comment #1)
> Found this bug another time in another incarnation.
> 
> Build with dmd -O for reproducing.
> 
> 
> --------- test4.d -------------
> 
> import core.simd;  
> 
> int4 cmpss_repro(float4 a)
> {
>     int4 result;
>     result.ptr[0] = (1 > a.array[0]) ? -1 : 0;
>     return result;
> }
> 
> -------------------------------

This particular example yields the output 
---

findreg(0, line=751, file='src/dmd/backend/cod4.d', function =
'_D5dtest11cmpss_reproFNhG4fZNhG4i')
dmd: src/dmd/backend/cgcod.d:1864: Assertion `0' failed.
---

The function in question: 
-------------------
reg_t findreg(regm_t regm, int line, const(char)* file)
{
    debug
    regm_t regmsave = regm;

    reg_t i = 0;
    while (1)
    {
        if (!(regm & 0xF))
        {
            regm >>= 4;
            i += 4;
            if (!regm)
                break;
        }
        if (regm & 1)
            return i;
        regm >>= 1;
        i++;
    }

    debug
    printf("findreg(%s, line=%d, file='%s', function =
'%s')\n",regm_str(regmsave),line,file,funcsym_p.Sident.ptr);
    fflush(stdout);

//    *(char*)0=0;
    assert(0);
}
-------------------

On the assumption that dmd builds are distributed after being compiled with
ldc, ldc (possibly dmd as well) will optimise an assert(0) to a x86 ud2
instruction.

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