Re: [PATCH] lra: Updates of biggest mode for hard regs [PR112278]

[Vladimir Makarov <vmakarov@redhat.com>]

On 12/3/23 05:13, Richard Sandiford wrote:
> [Gah.  In my head I'd sent this a few weeks ago, but it turns out
>   that I hadn't even got to the stage of writing the changlog...]
>
> LRA keeps track of the biggest mode for both hard registers and
> pseudos.  The updates assume that the modes are ordered, i.e. that
> we can tell whether one is no bigger than the other at compile time.
>
> That is (or at least seemed to be) a reasonable restriction for pseudos.
> But it isn't necessarily so for hard registers, since the uses of hard
> registers can be logically distinct.  The testcase is an example of this.
>
> The biggest mode of hard registers is also special for other reasons.
> As the existing comment says:
>
>    /* A reg can have a biggest_mode of VOIDmode if it was only ever seen as
>       part of a multi-word register.  In that case, just use the reg_rtx
>       mode.  Do the same also if the biggest mode was larger than a register
>       or we can not compare the modes.  Otherwise, limit the size to that of
>       the biggest access in the function or to the natural mode at least.  */
>
> This patch applies the same approach to the updates.
>
> Tested on aarch64-linus-gnu (with and without SVE) and on x86_64-linux-gnu.
> OK to install?
>
Sure.  Thank you for fixing this, Richard.