Re: [x86_64 PATCH] Two minor tweaks to ix86_expand_move.

[Uros Bizjak <ubizjak@gmail.com>]

On Fri, Jun 16, 2023 at 6:27 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch splits out two (independent) minor changes to i386-expand.cc's
> ix86_expand_move from a larger patch, given that it's better to review
> and commit these independent pieces separately from a more complex patch.
>
> The first change is to test for CONST_WIDE_INT_P before calling
> ix86_convert_const_wide_int_to_broadcast.  Whilst stepping through
> this function in gdb, I was surprised that the code was continually
> jumping into this function with operands that obviously weren't
> appropriate.
>
> The second change is to generalize the optimization for efficiently
> moving a TImode value to V1TImode (via V2DImode), to cover all 128-bit
> vector modes.
>
> Hence for the test case:
>
> typedef unsigned long uv2di __attribute__ ((__vector_size__ (16)));
> uv2di foo2(__int128 x) { return (uv2di)x; }
>
> we'd previously move via memory with:
>
> foo2:   movq    %rdi, -24(%rsp)
>         movq    %rsi, -16(%rsp)
>         movdqa  -24(%rsp), %xmm0
>         ret
>
> with this patch we now generate with -O2 (the same as V1TImode):
>
> foo2:   movq    %rdi, %xmm0
>         movq    %rsi, %xmm1
>         punpcklqdq      %xmm1, %xmm0
>         ret
>
> and with -O2 -msse4 the even better:
>
> foo2:   movq    %rdi, %xmm0
>         pinsrq  $1, %rsi, %xmm0
>         ret
>
> The new test case is unimaginatively called sse2-v1ti-mov-2.c given
> the original test case just for V1TI mode was called sse2-v1ti-mov-1.c.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures.  Ok for mainline?
>
>
> 2023-06-16  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * config/i386/i386-expand.cc (ix86_expand_move): Check that OP1 is
>         CONST_WIDE_INT_P before calling ix86_convert_wide_int_to_broadcast.
>         Generalize special case for converting TImode to V1TImode to handle
>         all 128-bit vector conversions.
>
> gcc/testsuite/ChangeLog
>         * gcc.target/i386/sse2-v1ti-mov-2.c: New test case.

OK.

Thanks,
Uros.

>
> Thanks in advance,
> Roger
> --
>