On Thu, 2020-10-08 at 09:27 +1030, Alan Modra via Gcc-patches wrote:
> The aim of this patch is to make rtx_costs for SETs closer to
> insn_cost for SETs. One visible effect on powerpc code is increased
> if-conversion.
>
> * config/rs6000/rs6000.c (rs6000_rtx_costs): Reduce cost of SET
> operands.
>
> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index 76aedbfae6f..d455aa52427 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -21684,6 +21684,35 @@ rs6000_rtx_costs (rtx x, machine_mode mode,
> int outer_code,
> }
> return false;
>
> + case SET:
> + /* On entry the value in *TOTAL is the number of general
> purpose
> + regs being set, multiplied by COSTS_N_INSNS (1). Handle
> + costing of set operands specially since in most cases we have
> + an instruction rather than just a piece of RTL and should
> + return a cost comparable to insn_cost. That's a little
> + complicated because in some cases the cost of SET operands is
> + non-zero, see point 5 above and cost of PLUS for example, and
> + in others it is zero, for example for (set (reg) (reg)).
> + But (set (reg) (reg)) has the same insn_cost as
> + (set (reg) (plus (reg) (reg))). Hack around this by
> + subtracting COSTS_N_INSNS (1) from the operand cost in cases
> + were we add at least COSTS_N_INSNS (1) for some operation.
s/were/where/ :-)
> + However, don't do so for constants. Constants might cost
> + more than zero when they require more than one instruction,
> + and we do want the cost of extra instructions. */
> + {
> + rtx_code src_code = GET_CODE (SET_SRC (x));
> + if (src_code == CONST_INT
> + || src_code == CONST_DOUBLE
> + || src_code == CONST_WIDE_INT)
> + return false;
> + int set_cost = (rtx_cost (SET_SRC (x), mode, SET, 1, speed)
> + + rtx_cost (SET_DEST (x), mode, SET, 0,
> speed));
> + if (set_cost >= COSTS_N_INSNS (1))
> + *total += set_cost - COSTS_N_INSNS (1);
> + return true;
> + }
> +
> default:
> return false;
> }
lgtm,
thanks
-Will
