Jonathan Wright <jonathan.wri...@arm.com> writes:
> Hi,
>
> A long time ago, using a parallel to take a subreg of a SIMD register
> was broken. This temporary fix[1] (from 2003) spilled these registers
> to memory and reloaded the appropriate part to obtain the subreg.
>
> The fix initially existed for the benefit of the PowerPC E500 - a
> platform for which GCC removed support a number of years ago.
> Regardless, a proper mechanism for taking a subreg of a SIMD register
> exists now anyway.
>
> This patch removes the workaround thus preventing SIMD registers
> being dumped to memory unnecessarily - which sometimes can't be fixed
> by later passes.
>
> Bootstrapped and regression tested on aarch64-none-linux-gnu and
> x86_64-pc-linux-gnu - no issues.
>
> Ok for master?
>
> Thanks,
> Jonathan
>
> [1] https://gcc.gnu.org/pipermail/gcc-patches/2003-April/102099.html
>
> ---
>
> gcc/ChangeLog:
>
> 2021-10-11 Jonathan Wright <jonathan.wri...@arm.com>
>
> * expr.c (emit_group_load_1): Remove historic workaround.
OK, thanks.
Richard
> diff --git a/gcc/expr.c b/gcc/expr.c
> index
> e0bcbccd9053df168c2e861414729fc7cf017f85..62446118b7beb725933ec6f7b0386e7e4b84fa90
> 100644
> --- a/gcc/expr.c
> +++ b/gcc/expr.c
> @@ -2508,19 +2508,6 @@ emit_group_load_1 (rtx *tmps, rtx dst, rtx orig_src,
> tree type,
> NULL);
> }
> }
> - /* FIXME: A SIMD parallel will eventually lead to a subreg of a
> - SIMD register, which is currently broken. While we get GCC
> - to emit proper RTL for these cases, let's dump to memory. */
> - else if (VECTOR_MODE_P (GET_MODE (dst))
> - && REG_P (src))
> - {
> - poly_uint64 slen = GET_MODE_SIZE (GET_MODE (src));
> - rtx mem;
> -
> - mem = assign_stack_temp (GET_MODE (src), slen);
> - emit_move_insn (mem, src);
> - tmps[i] = adjust_address (mem, mode, bytepos);
> - }
> else if (CONSTANT_P (src) && GET_MODE (dst) != BLKmode
> && XVECLEN (dst, 0) > 1)
> tmps[i] = simplify_gen_subreg (mode, src, GET_MODE (dst), bytepos);
