[committed] Fix failure of Octeon BADDU tests

[Richard Sandiford]

This patch fixes the MIPS octeon-baddu-1.c failures.  As Andrew says
in the PR, the problem is that the combined instruction seems more
expensive than the separate ones.

Tested on mips64-linux-gnu and applied.

Richard


gcc/
        PR target/51278
        * config/mips/mips.c (mips_rtx_costs): Handle baddu.

Index: gcc/config/mips/mips.c
===================================================================
--- gcc/config/mips/mips.c      2011-11-26 12:51:05.000000000 +0000
+++ gcc/config/mips/mips.c      2011-11-26 12:57:02.000000000 +0000
@@ -3777,6 +3777,16 @@ mips_rtx_costs (rtx x, int code, int out
       return false;
 
     case ZERO_EXTEND:
+      if (outer_code == SET
+         && ISA_HAS_BADDU
+         && (GET_CODE (XEXP (x, 0)) == TRUNCATE
+             || GET_CODE (XEXP (x, 0)) == SUBREG)
+         && GET_MODE (XEXP (x, 0)) == QImode
+         && GET_CODE (XEXP (XEXP (x, 0), 0)) == PLUS)
+       {
+         *total = set_src_cost (XEXP (XEXP (x, 0), 0), speed);
+         return true;
+       }
       *total = mips_zero_extend_cost (mode, XEXP (x, 0));
       return false;