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Subject: [Bug d/97843] Bad code gen when concatenating to array
Date: Mon, 16 Nov 2020 16:17:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97843

--- Comment #5 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
(In reply to Alex from comment #2)
> The arithmetic equivalent would be for:
> X +=3D 4/2
> To be produce:
> Immediate load Register with 4
> Add register with 4 in it to x
> Divide register with 4 in it by 2
> Resulting in x being increased by 4 instead of 2
>=20
> 10.2.3 Binary expressions EXCEPT for AssignExpression are left to right
>=20
> 10.2.7 says operand order is undefined
>=20
> Nowhere does the spec say that the assignment operator has to happen after
> operand evaluation. I think this is a hole in the spec.

The equivalent code that `bytes ~=3D bytes.sum` equates to is:

ref ubyte[] extend(ref ubyte[] bytes)
{
    bytes.length +=3D 1;
    bytes[$-1] =3D 0xde;
    return bytes;
}

extend(bytes)[bytes.length] =3D bytes.sum;

Which is also LTR evaluation, so everything is consistent so far.=