re PR rtl-optimization/7124 (-O2 -march=athlon produces ICE)

        PR opt/7124
        * config/i386/i386.c (ix86_register_move_cost): Increase cost
        for secondary_memory_needed pairs.

From-SVN: r57751

gcc/ChangeLog

-2002-10-02  Matt Austern  <austern@apple.com
+2002-10-02  Richard Henderson  <rth@redhat.com>
+
+	PR opt/7124
+	* config/i386/i386.c (ix86_register_move_cost): Increase cost
+	for secondary_memory_needed pairs.
+
+2002-10-02  Matt Austern  <austern@apple.com>
+
 	* class.c (check_field_decls): Changed warning about const member
 	variables so that it doesn't get issued for a class aggregate.
 	

gcc/config/i386/i386.c

@@ -13580,17 +13580,33 @@ ix86_register_move_cost (mode, class1, class2)
      enum reg_class class1, class2;
 {
   /* In case we require secondary memory, compute cost of the store followed
-     by load.  In case of copying from general_purpose_register we may emit
-     multiple stores followed by single load causing memory size mismatch
-     stall.  Count this as arbitarily high cost of 20.  */
+     by load.  In order to avoid bad register allocation choices, we need 
+     for this to be *at least* as high as the symmetric MEMORY_MOVE_COST.  */
+
   if (ix86_secondary_memory_needed (class1, class2, mode, 0))
     {
-      int add_cost = 0;
+      int cost = 1;
+
+      cost += MAX (MEMORY_MOVE_COST (mode, class1, 0),
+		   MEMORY_MOVE_COST (mode, class1, 1));
+      cost += MAX (MEMORY_MOVE_COST (mode, class2, 0),
+		   MEMORY_MOVE_COST (mode, class2, 1));
+      
+      /* In case of copying from general_purpose_register we may emit multiple
+         stores followed by single load causing memory size mismatch stall.
+         Count this as arbitarily high cost of 20.  */
       if (CLASS_MAX_NREGS (class1, mode) > CLASS_MAX_NREGS (class2, mode))
-	  add_cost = 20;
-      return (MEMORY_MOVE_COST (mode, class1, 0)
-	      + MEMORY_MOVE_COST (mode, class2, 1) + add_cost);
+	cost += 20;
+
+      /* In the case of FP/MMX moves, the registers actually overlap, and we
+	 have to switch modes in order to treat them differently.  */
+      if ((MMX_CLASS_P (class1) && MAYBE_FLOAT_CLASS_P (class2))
+          || (MMX_CLASS_P (class2) && MAYBE_FLOAT_CLASS_P (class1)))
+	cost += 20;
+
+      return cost;
     }
+
   /* Moves between SSE/MMX and integer unit are expensive.  */
   if (MMX_CLASS_P (class1) != MMX_CLASS_P (class2)
       || SSE_CLASS_P (class1) != SSE_CLASS_P (class2))