[PATCH][ARM][2/4] Fix operand costing logic for SMUL[TB][TB]

[Kyrill Tkachov]

Hi all,

As part of investigating the codegen effects of a fix for PR 65932 I found we 
assign
too high a cost for the sign-extending multiply instruction SMULBB.
This is because we add the cost of a multiply-extend but then also recurse into 
the
SIGN_EXTEND sub-expressions rather than the registers (or subregs) being 
sign-extended.

This patch is a simple fix. The fix is right by itself, but in combination with 
patch 3
fix the gcc.target/arm/wmul-2.c testcase.

Bootstrapped and tested on arm-none-linux-gnueabihf.

Ok for trunk?

Thanks,
Kyrill

2016-01-22  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    * config/arm/arm.c (arm_new_rtx_costs, MULT case): Properly extract
    the operands of the SIGN_EXTENDs from a SMUL[TB][TB] rtx.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 17f00b5a1de21de35366b82040a7ad46d65f899e..ee3ebe4561ea3d9791fabdfcec8b16af63bd4d20 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -10321,8 +10321,10 @@ arm_new_rtx_costs (rtx x, enum rtx_code code, enum rtx_code outer_code,
 	      /* SMUL[TB][TB].  */
 	      if (speed_p)
 		*cost += extra_cost->mult[0].extend;
-	      *cost += rtx_cost (XEXP (x, 0), mode, SIGN_EXTEND, 0, speed_p);
-	      *cost += rtx_cost (XEXP (x, 1), mode, SIGN_EXTEND, 1, speed_p);
+	      *cost += rtx_cost (XEXP (XEXP (x, 0), 0), mode,
+				 SIGN_EXTEND, 0, speed_p);
+	      *cost += rtx_cost (XEXP (XEXP (x, 1), 0), mode,
+				 SIGN_EXTEND, 1, speed_p);
 	      return true;
 	    }
 	  if (speed_p)