RFA: RL78: Fix multiply costs when optimizing for size

[Nick Clifton]

Hi DJ,

  The patch below fixes a small problem with the RL78 backend.  When
  optimizing for size it is better to use a slow multiply instruction
  than a faster, but larger, shift sequence.  So the patch tweaks the
  rtx costs for MULT insns when speed is not a priority.

  Tested with no regressions on an rl78-elf toolchain.

  OK to apply ?

Cheers
  Nick

gcc/ChangeLog
2015-08-05  Nick Clifton  <ni...@redhat.com>

        * config/rl78/rl78.c (rl78_rtx_costs): Treat MULT insns as cheap
        if optimizing for size.

Index: gcc/config/rl78/rl78.c
===================================================================
RCS file: /cvs/cvsfiles/gnupro/gcc/config/rl78/rl78.c,v
retrieving revision 1.12.6.15
diff -u -3 -p -r1.12.6.15 rl78.c
--- gcc/config/rl78/rl78.c      29 Jul 2015 12:24:04 -0000      1.12.6.15
+++ gcc/config/rl78/rl78.c      30 Jul 2015 15:20:10 -0000
@@ -4161,7 +4161,9 @@ static bool rl78_rtx_costs (rtx   x,
       switch (code)
        {
        case MULT:
-         if (RL78_MUL_G14)
+         if (! speed)
+           * total = COSTS_N_INSNS (5);
+         else if (RL78_MUL_G14)
            *total = COSTS_N_INSNS (14);
          else if (RL78_MUL_G13)
            *total = COSTS_N_INSNS (29);