Re: [PATCH][GCC][AArch64] Allow any offset for SVE addressing modes before reload

[Richard Sandiford]

Tamar Christina <tamar.christ...@arm.com> writes:
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 
> 5df5a8b78439e69705e62845a4d1f86166a01894..59f03e688e58c1aab37629555c7b3f19e5075935
>  100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -3414,6 +3414,14 @@ aarch64_expand_mov_immediate (rtx dest, rtx imm,
>  void
>  aarch64_emit_sve_pred_move (rtx dest, rtx pred, rtx src)
>  {
> +  /* Make sure that the address is legitimate.  */
> +  if (MEM_P (dest)
> +      && !aarch64_sve_struct_memory_operand_p (dest))
> +    {
> +      rtx addr = force_reg (Pmode, XEXP (dest, 0));
> +      dest = replace_equiv_address (dest, addr);
> +    }
> +
>    emit_insn (gen_rtx_SET (dest, gen_rtx_UNSPEC (GET_MODE (dest),
>                                               gen_rtvec (2, pred, src),
>                                               UNSPEC_MERGE_PTRUE)));

I think the same thing could happen for the src as well as dest.
The function is also used for single-vector modes, not just struct modes.

This code predated the support for "@" patterns.  Now that we have them,
it might be better to make:

(define_insn "*pred_mov<mode>"
  [(set (match_operand:SVE_ALL 0 "nonimmediate_operand" "=w, m")
        (unspec:SVE_ALL
          [(match_operand:<VPRED> 1 "register_operand" "Upl, Upl")
           (match_operand:SVE_ALL 2 "nonimmediate_operand" "m, w")]
          UNSPEC_MERGE_PTRUE))]

and:

(define_insn_and_split "pred_mov<mode>"
  [(set (match_operand:SVE_STRUCT 0 "aarch64_sve_struct_nonimmediate_operand" 
"=w, Utx")
        (unspec:SVE_STRUCT
          [(match_operand:<VPRED> 1 "register_operand" "Upl, Upl")
           (match_operand:SVE_STRUCT 2 
"aarch64_sve_struct_nonimmediate_operand" "Utx, w")]
          UNSPEC_MERGE_PTRUE))]

public as "@aarch64_pred_mov<mode>" ("aarch64_" so that we don't
pollute the target-independent namespace).  Then we can use something like:

  expand_operand ops[3];
  create_output_operand (&ops[0], dest, mode);
  create_input_operand (&ops[1], pred, GET_MODE (pred));
  create_input_operand (&ops[2], src, mode);
  expand_insn (code_for_aarch64_pred_mov (mode), 3, ops);

(completely untested).

Thanks,
Richard