Re: [PATCH] Also preserve SUBREG_PROMOTED_VAR_P in expr.c's convert_move.

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/11/2021 3:28 AM, Roger Sayle wrote:
> This patch catches another place in the middle-end where it's possible
> to preserve the SUBREG_PROMOTED_VAR_P annotation on a subreg to the
> benefit of later RTL optimizations.  This adds the same logic to
> expr.c's convert_move as recently added to convert_modes.
>
> On nvptx-none, the simple test program:
>
> short foo (char c) { return c; }
>
> currently generates three instructions:
>
> mov.u32 %r23, %ar0;
> cvt.u16.u32     %r24, %r23;
> cvt.s32.s16     %value, %r24;
>
> with this patch, we now generate just one:
>
> mov.u32 %value, %ar0;
>
>
> This patch should look familiar, it's almost identical to the recent patch
> https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578331.html but with
> the fix https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578519.html
> [Apologies again for this breakage on affected (non-x86_64) targets; I hope
> having that fixed within a few hours (before many folks even noticed a
> problem) minimized the inconvenience].
>
> This patch has been tested on x86_64-pc-linux-gnu with "make bootstrap"
> and "make -k check" with no new failures, and on a cross-compiler to
> nvptx-none, with no new failures in its testsuite.  OK for mainline?
>
>
> 2021-09-11  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
> 	* expr.c (convert_move): Preserve SUBREG_PROMOTED_VAR_P when
> 	creating a (wider) partial subreg from a SUBREG_PROMOTED_VAR_P
> 	subreg.
OK

Jeff