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[0/3] Fix PR78120, in ifcvt/rtlanal/i386.

Message ID 90a82189-d776-c568-0989-dd33b121337a@redhat.com
State New
Headers show

Commit Message

Bernd Schmidt Nov. 23, 2016, 7:01 p.m. UTC 
On 11/23/2016 07:57 PM, Bernd Schmidt wrote:
> 2. The i386 backend mishandles SET rtxs. If you have a fairly plain

> single-insn SET, you tend to get COSTS_N_INSNS (2) out of set_rtx_cost,

> because rtx_costs has a default of COSTS_N_INSNS (1) for a SET, and you

> get the cost of the src in addition to that.



Bernd

Comments

Uros Bizjak Nov. 23, 2016, 9:46 p.m. UTC | #1 
On Wed, Nov 23, 2016 at 8:01 PM, Bernd Schmidt <bschmidt@redhat.com> wrote:
> On 11/23/2016 07:57 PM, Bernd Schmidt wrote:

>>

>> 2. The i386 backend mishandles SET rtxs. If you have a fairly plain

>> single-insn SET, you tend to get COSTS_N_INSNS (2) out of set_rtx_cost,

>> because rtx_costs has a default of COSTS_N_INSNS (1) for a SET, and you

>> get the cost of the src in addition to that.


Looks good to me.

Thanks,
Uros.
diff mbox

Patch

	PR rtl-optimization/78120
	* config/i386/i386.c (ix86_rtx_costs): Fully handle SETs.

Index: gcc/config/i386/i386.c
===================================================================
--- gcc/config/i386/i386.c	(revision 242038)
+++ gcc/config/i386/i386.c	(working copy)
@@ -39925,6 +39925,7 @@  ix86_rtx_costs (rtx x, machine_mode mode
   enum rtx_code code = GET_CODE (x);
   enum rtx_code outer_code = (enum rtx_code) outer_code_i;
   const struct processor_costs *cost = speed ? ix86_cost : &ix86_size_cost;
+  int src_cost;
 
   switch (code)
     {
@@ -39935,7 +39936,23 @@  ix86_rtx_costs (rtx x, machine_mode mode
 	  *total = ix86_set_reg_reg_cost (GET_MODE (SET_DEST (x)));
 	  return true;
 	}
-      return false;
+
+      if (register_operand (SET_SRC (x), VOIDmode))
+	/* Avoid potentially incorrect high cost from rtx_costs
+	   for non-tieable SUBREGs.  */
+	src_cost = 0;
+      else
+	{
+	  src_cost = rtx_cost (SET_SRC (x), mode, SET, 1, speed);
+
+	  if (CONSTANT_P (SET_SRC (x)))
+	    /* Constant costs assume a base value of COSTS_N_INSNS (1) and add
+	       a small value, possibly zero for cheap constants.  */
+	    src_cost += COSTS_N_INSNS (1);
+	}
+
+      *total = src_cost + rtx_cost (SET_DEST (x), mode, SET, 0, speed);
+      return true;
 
     case CONST_INT:
     case CONST: