Patchwork [AArch64,costs,7/18] Improve SET cost.

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Submitter James Greenhalgh
Date March 27, 2014, 5:33 p.m.
Message ID <1395941622-22926-8-git-send-email-james.greenhalgh@arm.com>
Download mbox | patch
Permalink /patch/334430/
State New
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Comments

James Greenhalgh - March 27, 2014, 5:33 p.m.
Hi,

This patch adds functionality for costing a SET RTX.

Often these are "free" in the sense that we factor the cost of the set
in to the cost of the RHS of the insn. Notable exceptions are sets to
MEM which should be costed as a store, and simple register moves, which
should be costed.

Tested in series on aarch64-none-elf.

OK for stage 1?

Thanks,
James

---
2014-03-27  James Greenhalgh  <james.greenhalgh@arm.com>
	    Philip Tomsich  <philipp.tomsich@theobroma-systems.com>

	* config/aarch64/aarch64.c (aarch64_rtx_costs): Improve costing
	for SET RTX.

Patch

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 766d70d..1b21ecc 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -4826,6 +4826,8 @@  aarch64_rtx_costs (rtx x, int code, int outer ATTRIBUTE_UNUSED,
   switch (code)
     {
     case SET:
+      /* The cost depends entirely on the operands to SET.  */
+      *cost = 0;
       op0 = SET_DEST (x);
       op1 = SET_SRC (x);
 
@@ -4835,23 +4837,33 @@  aarch64_rtx_costs (rtx x, int code, int outer ATTRIBUTE_UNUSED,
 	  if (speed)
 	    *cost += extra_cost->ldst.store;
 
-	  if (op1 != const0_rtx)
-	    *cost += rtx_cost (op1, SET, 1, speed);
+	  *cost += rtx_cost (op1, SET, 1, speed);
 	  return true;
 
 	case SUBREG:
 	  if (! REG_P (SUBREG_REG (op0)))
 	    *cost += rtx_cost (SUBREG_REG (op0), SET, 0, speed);
+
 	  /* Fall through.  */
 	case REG:
-	  /* Cost is just the cost of the RHS of the set.  */
-	  *cost += rtx_cost (op1, SET, 1, true);
+	  /* const0_rtx is in general free, but we will use an
+	     instruction to set a register to 0.  */
+          if (REG_P (op1) || op1 == const0_rtx)
+            {
+              /* The cost is 1 per register copied.  */
+              int n_minus_1 = (GET_MODE_SIZE (GET_MODE (op0)) - 1)
+			      / UNITS_PER_WORD;
+              *cost = COSTS_N_INSNS (n_minus_1 + 1);
+            }
+          else
+	    /* Cost is just the cost of the RHS of the set.  */
+	    *cost += rtx_cost (op1, SET, 1, speed);
 	  return true;
 
-	case ZERO_EXTRACT:  /* Bit-field insertion.  */
+	case ZERO_EXTRACT:
 	case SIGN_EXTRACT:
-	  /* Strip any redundant widening of the RHS to meet the width of
-	     the target.  */
+	  /* Bit-field insertion.  Strip any redundant widening of
+	     the RHS to meet the width of the target.  */
 	  if (GET_CODE (op1) == SUBREG)
 	    op1 = SUBREG_REG (op1);
 	  if ((GET_CODE (op1) == ZERO_EXTEND
@@ -4860,10 +4872,25 @@  aarch64_rtx_costs (rtx x, int code, int outer ATTRIBUTE_UNUSED,
 	      && (GET_MODE_BITSIZE (GET_MODE (XEXP (op1, 0)))
 		  >= INTVAL (XEXP (op0, 1))))
 	    op1 = XEXP (op1, 0);
-	  *cost += rtx_cost (op1, SET, 1, speed);
+
+          if (CONST_INT_P (op1))
+            {
+              /* MOV immediate is assumed to always be cheap.  */
+              *cost = COSTS_N_INSNS (1);
+            }
+          else
+            {
+              /* BFM.  */
+	      if (speed)
+		*cost += extra_cost->alu.bfi;
+              *cost += rtx_cost (op1, (enum rtx_code) code, 1, speed);
+            }
+
 	  return true;
 
 	default:
+	  /* We can't make sense of this, assume default cost.  */
+          *cost = COSTS_N_INSNS (1);
 	  break;
 	}
       return false;