Re: RFA: enable LRA for rs6000

[David Edelsohn <dje dot gcc at gmail dot com>]

On Fri, Apr 12, 2013 at 12:57 PM, Vladimir Makarov <vmakarov@redhat.com> wrote:

> After thorough investigation I found that this code is still ok.  The
> explanations are in the comment.  Here is the modified version of the code
> taking you proposals into account
>
> @@ -5701,19 +5705,31 @@ legitimate_lo_sum_address_p (enum machin
>
>    if (TARGET_ELF || TARGET_MACHO)
>      {
> +      bool large_toc_ok;
> +
>        if (DEFAULT_ABI != ABI_AIX && DEFAULT_ABI != ABI_DARWIN && flag_pic)
>         return false;
> -      if (TARGET_TOC)
> +      /* LRA don't use LEGITIMIZE_RELOAD_ADDRESS as it usually calls
> +        push_reload from reload pass code. LEGITIMIZE_RELOAD_ADDRESS
> +        recognizes some LO_SUM addresses as valid although this
> +        function says opposite.  In most cases, LRA through different
> +        transformations can generate correct code for address reloads.
> +        It can not manage only some LO_SUM cases.  So we need to add
> +        code analogous to one in rs6000_legitimize_reload_address for
> +        LOW_SUM here saying that some addresses are still valid. */
> +      large_toc_ok = (lra_in_progress && TARGET_CMODEL != CMODEL_SMALL
>
> +                     && small_toc_ref (x, VOIDmode));
> +      if (TARGET_TOC && ! large_toc_ok)
>         return false;
>        if (GET_MODE_NUNITS (mode) != 1)
>         return false;
> -      if (GET_MODE_SIZE (mode) > UNITS_PER_WORD
> +      if (! lra_in_progress && GET_MODE_SIZE (mode) > UNITS_PER_WORD
>           && !(/* ??? Assume floating point reg based on mode?  */
>                TARGET_HARD_FLOAT && TARGET_FPRS && TARGET_DOUBLE_FLOAT
>                && (mode == DFmode || mode == DDmode)))
>         return false;
>
> -      return CONSTANT_P (x);
> +      return CONSTANT_P (x) || large_toc_ok;
>      }
>
>    return false;

Okay, this makes more sense.

I think that Mike is running some experiments with LRA to see what
impact we see.  I would like to understand that a little more before
we apply the patch to trunk.

Thanks David