RFA: RL78: Fix multiply costs when optimizing for size

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  <nickc@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);

Re: RFA: RL78: Fix multiply costs when optimizing for size

[DJ Delorie]

>   OK to apply ?

Ok.  Thanks!

> gcc/ChangeLog
> 2015-08-05  Nick Clifton  <nickc@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);
>