[PATCH] emit-rtl.c: Allow vector subreg of float vectors

[Richard Sandiford]

Andrew Stubbs <ams@codesourcery.com> writes:
> This patch is a prerequisite for some patches I have to add multiple 
> vector sizes on amdgcn.
>
> The problem is that validate_subreg rejects things like this:
>
>    (subreg:V32SF (reg:V64SF) 0)
>
> These are commonly generated by the compiler. The integer equivalents 
> work fine.
>
> To be honest, I don't know why other targets have not encountered this 
> problem before? Perhaps because most other targets require all vectors 
> to have the same number of bits, meaning that float vectors have a fixed 
> number of lanes? In my case, amdgcn can convert V64SFmode to V32SFmode 
> by simply masking off some lanes.
>
> OK to commit? (I have an x86_64 bootstrap and test in progress.)
>
> Andrew
>
> Allow vector subreg of float vectors
>
> Integer vector subregs were already permitted.
>
> gcc/ChangeLog:
>
> 	* emit-rtl.c (validate_subreg): Permit sections of float vectors.
>
> diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
> index f9b0e9714d9..d7067989ad7 100644
> --- a/gcc/emit-rtl.c
> +++ b/gcc/emit-rtl.c
> @@ -947,6 +947,11 @@ validate_subreg (machine_mode omode, machine_mode imode,
>    else if (VECTOR_MODE_P (omode)
>  	   && GET_MODE_INNER (omode) == GET_MODE_INNER (imode))
>      ;
> +  /* Allow sections of vectors, both smaller and paradoxical.  (This just
> +     works for integers, but needs to be explicitly allowed for floats.)  */
> +  else if (VECTOR_MODE_P (omode) && VECTOR_MODE_P (imode)
> +	   && GET_MODE_INNER (omode) == GET_MODE_INNER (imode))
> +    ;

Might be missing something, but isn't this a subcondition of the
previous “else if”?  It looks like that ought to catch every case
that the new one does.

Thanks,
Richard

>    /* Subregs involving floating point modes are not allowed to
>       change size.  Therefore (subreg:DI (reg:DF) 0) is fine, but
>       (subreg:SI (reg:DF) 0) isn't.  */