On Fri, Sep 18, 2020 at 01:13:18PM -0500, Segher Boessenkool wrote:
> Thanks (to both of you). Interesting! Which of these unrelated changes
> does this come from?
Most of the changes I saw in code generation (not in spec, I didn't
look there, but in gcc) came down to this change to the cost for SETs,
and "rs6000_rtx_costs multi-insn constants". I expect they were the
changes that made most difference to spec results, with this patch
likely resulting in more if-conversion.
So here is the patch again, this time without any distracting other
changes. With a further revised comment.
* 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 8969baa4dcf..2d770afd8fe 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -21599,6 +21599,35 @@ rs6000_rtx_costs (rtx x, machine_mode mode, int
outer_code,
}
break;
+ 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.
+ 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:
break;
}
--
Alan Modra
Australia Development Lab, IBM
