Use enums for the index of IL operands.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 29065)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -4161,8 +4161,8 @@
         StoreInstanceFieldInstr* store_instance_field =
             instr->AsStoreInstanceField();
         kind_ = kField;
-        // Value is at input index 1.
-        representation_ = store_instance_field->RequiredInputRepresentation(1);
+        representation_ = store_instance_field->
+            RequiredInputRepresentation(StoreInstanceFieldInstr::kValuePos);
         instance_ =
             OriginalDefinition(store_instance_field->instance()->definition());
         field_ = &store_instance_field->field();
@@ -4172,8 +4172,8 @@
       case Instruction::kStoreVMField: {
         StoreVMFieldInstr* store_vm_field = instr->AsStoreVMField();
         kind_ = kVMField;
-        // Value is at input index 0.
-        representation_ = store_vm_field->RequiredInputRepresentation(0);
+        representation_ = store_vm_field->
+            RequiredInputRepresentation(StoreVMFieldInstr::kValuePos);
         instance_ = OriginalDefinition(store_vm_field->dest()->definition());
         offset_in_bytes_ = store_vm_field->offset_in_bytes();
         break;
@@ -4188,9 +4188,8 @@
 
       case Instruction::kStoreStaticField:
         kind_ = kField;
-        // Value is at input index 0.
-        representation_ =
-            instr->AsStoreStaticField()->RequiredInputRepresentation(0);
+        representation_ = instr->AsStoreStaticField()->
+            RequiredInputRepresentation(StoreStaticFieldInstr::kValuePos);
         field_ = &instr->AsStoreStaticField()->field();
         break;
 
@@ -4207,8 +4206,8 @@
       case Instruction::kStoreIndexed: {
         StoreIndexedInstr* store_indexed = instr->AsStoreIndexed();
         kind_ = kIndexed;
-        // Value is at input index 2.
-        representation_ = store_indexed->RequiredInputRepresentation(2);
+        representation_ = store_indexed->
+            RequiredInputRepresentation(StoreIndexedInstr::kValuePos);
         instance_ = OriginalDefinition(store_indexed->array()->definition());
         index_ = store_indexed->index()->definition();
         break;
@@ -4223,8 +4222,8 @@
 
       case Instruction::kStoreContext:
         kind_ = kContext;
-        ASSERT(instr->AsStoreContext()->RequiredInputRepresentation(0) ==
-               kTagged);
+        ASSERT(instr->AsStoreContext()->RequiredInputRepresentation(
+            StoreContextInstr::kValuePos) == kTagged);
         representation_ = kTagged;
         break;