[PATCH][AArch64] Properly handle simple arith+extend ops in rtx costs

[Kyrill Tkachov]

Hi all,

Currently we assign the wrong rtx cost to instructions of the form
  add     x0, x0, x1, sxtw

that is, an arith operation plus a single extend (no shifting).
We correctly catch the cases where the extend is inside a shift, but
not the simple case.

This patch fixes that oversight by catching the simple case in
aarch64_rtx_arith_op_extract_p and thus making sure that it gets
assigned the alu.extend_arith extra cost.

Bootstrapped and tested on aarch64.

Ok for trunk?
Thanks,
Kyrill


2015-07-28  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    * config/aarch64/aarch64.c (aarch64_rtx_arith_op_extract_p):
    Handle simple SIGN_EXTEND or ZERO_EXTEND.
    (aarch64_rtx_costs): Properly strip extend or extract before
    passing down to rtx costs again.

commit 6ad208ea10b0893b356dab9d0c6f59821441229c
Author: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
Date:   Fri Jul 24 15:02:10 2015 +0100

    [AArch64] Properly handle simple arith+extend ops in rtx costs

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 617c079..eb70c30 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -5622,6 +5622,11 @@ aarch64_rtx_arith_op_extract_p (rtx x, machine_mode mode)
 	  return true;
 	}
     }
+  /* The simple case <ARITH>, XD, XN, XM, [us]xt.
+     No shift.  */
+  else if (GET_CODE (x) == SIGN_EXTEND
+	   || GET_CODE (x) == ZERO_EXTEND)
+    return REG_P (XEXP (x, 0));
 
   return false;
 }
@@ -6133,7 +6138,8 @@ cost_minus:
 	    if (speed)
 	      *cost += extra_cost->alu.extend_arith;
 
-	    *cost += rtx_cost (XEXP (XEXP (op1, 0), 0), VOIDmode,
+	    op1 = aarch64_strip_extend (op1);
+	    *cost += rtx_cost (op1, VOIDmode,
 			       (enum rtx_code) GET_CODE (op1), 0, speed);
 	    return true;
 	  }
@@ -6211,7 +6217,8 @@ cost_plus:
 	    if (speed)
 	      *cost += extra_cost->alu.extend_arith;
 
-	    *cost += rtx_cost (XEXP (XEXP (op0, 0), 0), VOIDmode,
+	    op0 = aarch64_strip_extend (op0);
+	    *cost += rtx_cost (op0, VOIDmode,
 			       (enum rtx_code) GET_CODE (op0), 0, speed);
 	    return true;
 	  }