[PATCH] hppa: Improve hppa_rtx_costs for shifts by constants.

[Roger Sayle]

Hi Dave (and Jeff),
For your consideration, here's a patch that should fix the recent regression
of gcc.dg/tree-ssa/slrt-13.c on hppa targets.

This patch provides more accurate rtx_costs estimates for shifts by
integer constants (which are cheaper than by a register amount).
Fine tuning these is sufficient to have simple-ssa-strength-reduce
prefer multiplications by four, over multiplications by five.

Technically only the ASHIFT is required to fix the regression, but for
symmetry
I've added the appropriate PA-RISC values for all three shift types (in
SImode).
I've also checked that this doesn't reintroduce PR middle-end/87256.

I was wondering whether you could please "put this in the queue", and
reconfirm that PR middle-end/87256 remains resolved?


2020-08-27  Roger Sayle  <ro...@nextmovesoftware.com>

gcc/ChangeLog
        * config/pa/pa.c (hppa_rtx_costs) [ASHIFT, ASHIFTRT, LSHIFTRT]:
        Provide accurate costs for shifts of integer constants.

Many thanks in advance (and my apologies for the inconvenience),
Roger
--
Roger Sayle
NextMove Software
Cambridge, UK


diff --git a/gcc/config/pa/pa.c b/gcc/config/pa/pa.c
index cb88852..a9223ab 100644
--- a/gcc/config/pa/pa.c
+++ b/gcc/config/pa/pa.c
@@ -1642,6 +1642,14 @@ hppa_rtx_costs (rtx x, machine_mode mode, int outer_code,
          else
            *total = COSTS_N_INSNS (18);
        }
+      else if (REG_P (XEXP (x, 0)) && CONST_INT_P (XEXP (x, 1)))
+       {
+         if (TARGET_64BIT)
+           *total = COSTS_N_INSNS (2);
+         else
+           *total = COSTS_N_INSNS (1);
+         return true;
+       }
       else if (TARGET_64BIT)
        *total = COSTS_N_INSNS (4);
       else
@@ -1665,6 +1673,14 @@ hppa_rtx_costs (rtx x, machine_mode mode, int outer_code,
          else
            *total = COSTS_N_INSNS (19);
        }
+      else if (REG_P (XEXP (x, 0)) && CONST_INT_P (XEXP (x, 1)))
+       {
+         if (TARGET_64BIT)
+           *total = COSTS_N_INSNS (2);
+         else
+           *total = COSTS_N_INSNS (1);
+         return true;
+       }
       else if (TARGET_64BIT)
        *total = COSTS_N_INSNS (4);
       else
@@ -1688,6 +1704,11 @@ hppa_rtx_costs (rtx x, machine_mode mode, int outer_code,
          else
            *total = COSTS_N_INSNS (15);
        }
+      else if (REG_P (XEXP (x, 0)) && CONST_INT_P (XEXP (x, 1)))
+       {
+         *total = COSTS_N_INSNS (1);
+         return true;
+       }
       else if (TARGET_64BIT)
        *total = COSTS_N_INSNS (3);
       else