[backport from gcc-4.7/trunk <mikpe@it.uu.se>]

gcc/

2011-03-16  Jeff Law  <law@redhat.com>

	PR rtl-optimization/37273
	* ira-costs.c (scan_one_insn): Detect constants living in memory and
	handle them like argument loads from stack slots.  Do not double
	count memory for memory constants and argument loads from stack slots.

--- gcc-4.6-20110318/gcc/ira-costs.c.~1~	2011-02-15 22:21:59.000000000 +0100
+++ gcc-4.6-20110318/gcc/ira-costs.c	2011-03-21 14:35:51.000000000 +0100
@@ -1,5 +1,5 @@
 /* IRA hard register and memory cost calculation for allocnos or pseudos.
-   Copyright (C) 2006, 2007, 2008, 2009, 2010
+   Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011
    Free Software Foundation, Inc.
    Contributed by Vladimir Makarov <vmakarov@redhat.com>.
 
@@ -1009,6 +1009,7 @@ scan_one_insn (rtx insn)
   enum rtx_code pat_code;
   rtx set, note;
   int i, k;
+  bool counted_mem;
 
   if (!NONDEBUG_INSN_P (insn))
     return insn;
@@ -1018,15 +1019,23 @@ scan_one_insn (rtx insn)
       || pat_code == ADDR_VEC || pat_code == ADDR_DIFF_VEC)
     return insn;
 
+  counted_mem = false;
   set = single_set (insn);
   extract_insn (insn);
 
   /* If this insn loads a parameter from its stack slot, then it
      represents a savings, rather than a cost, if the parameter is
-     stored in memory.  Record this fact.  */
+     stored in memory.  Record this fact. 
+
+     Similarly if we're loading other constants from memory (constant
+     pool, TOC references, small data areas, etc) and this is the only
+     assignment to the destination pseudo.  */
   if (set != 0 && REG_P (SET_DEST (set)) && MEM_P (SET_SRC (set))
       && (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != NULL_RTX
-      && MEM_P (XEXP (note, 0)))
+      && ((MEM_P (XEXP (note, 0)))
+	  || (CONSTANT_P (XEXP (note, 0))
+	      && LEGITIMATE_CONSTANT_P (XEXP (note, 0))
+	      && REG_N_SETS (REGNO (SET_DEST (set))) == 1)))
     {
       enum reg_class cl = GENERAL_REGS;
       rtx reg = SET_DEST (set);
@@ -1038,6 +1047,7 @@ scan_one_insn (rtx insn)
 	-= ira_memory_move_cost[GET_MODE (reg)][cl][1] * frequency;
       record_address_regs (GET_MODE (SET_SRC (set)), XEXP (SET_SRC (set), 0),
 			   0, MEM, SCRATCH, frequency * 2);
+      counted_mem = true;
     }
 
   record_operand_costs (insn, pref);
@@ -1052,7 +1062,10 @@ scan_one_insn (rtx insn)
 	struct costs *p = COSTS (costs, COST_INDEX (regno));
 	struct costs *q = op_costs[i];
 
-	p->mem_cost += q->mem_cost;
+	/* If the already accounted for the memory "cost" above, don't
+	   do so again.  */
+	if (!counted_mem)
+	  p->mem_cost += q->mem_cost;
 	for (k = 0; k < cost_classes_num; k++)
 	  p->cost[k] += q->cost[k];
       }