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RFA: RL78: Fix multiply costs when optimizing for size
- From: Nick Clifton <nickc at redhat dot com>
- To: dj at redhat dot com
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 05 Aug 2015 14:52:32 +0100
- Subject: RFA: RL78: Fix multiply costs when optimizing for size
- Authentication-results: sourceware.org; auth=none
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);