Re: [PATCH] Fix emit_group_store regression on big-endian

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Oct 12, 2022 at 1:01 AM Eric Botcazou via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> the recent optimization implemented for complex modes in:
>   https://gcc.gnu.org/pipermail/gcc-patches/2022-May/595865.html
> contains an oversight for big-endian platforms in the "interesting corner
> case" mentioned in the message: it uses a lowpart SUBREG when the integer
> modes have different sizes, but this does not match the semantics of the
> PARALLELs which have a bundled byte offset; this offset is always zero in the
> code path and the lowpart is not at offset zero on big-endian platforms.
>
> Calling validate_subreg with this zero offset would fix the regression by
> disabling the optimization on big-endian platforms, so instead the attached
> fix adds the appropriate right shift for them.
>
> This fixes the following regressions in the C testsuite on SPARC64/Linux:
> FAIL: gcc.c-torture/execute/20041124-1.c   -O0  execution test
> FAIL: gcc.c-torture/execute/20041124-1.c   -O1  execution test
> FAIL: gcc.c-torture/execute/20041124-1.c   -O2  execution test
> FAIL: gcc.c-torture/execute/20041124-1.c   -O2 -flto -fno-use-linker-plugin -
> flto-partition=none  execution test
> FAIL: gcc.c-torture/execute/20041124-1.c   -O2 -flto -fuse-linker-plugin -fno-
> fat-lto-objects  execution test
> FAIL: gcc.c-torture/execute/20041124-1.c   -O3 -g  execution test
> FAIL: gcc.c-torture/execute/20041124-1.c   -Os  execution test
> FAIL: gcc.dg/compat/struct-by-value-11 c_compat_x_tst.o-c_compat_y_tst.o
> execute
> FAIL: gcc.dg/compat/struct-by-value-12 c_compat_x_tst.o-c_compat_y_tst.o
> execute
> FAIL: tmpdir-gcc.dg-struct-layout-1/t027 c_compat_x_tst.o-c_compat_y_tst.o
> execute
>
> Tested on SPARC64/Linux, OK for the mainline?

OK.

Thanks,
Richard.

>
> 2022-10-11  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * expr.cc (emit_group_stote): Fix handling of modes of different
>         sizes for big-endian targets in latest change and add commentary.
>
> --
> Eric Botcazou