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

[Bernd Schmidt <bschmidt@redhat.com>]

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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


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	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: