Propagate this-specialization to regular (megamorphic) calls

runtime/vm/flow_graph.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 65 matching lines @@
     }
   } else if (FLAG_trace_optimization) {
     if (current_defn == NULL) {
       THR_Print("Removing %s\n", current->DebugName());
     } else {
       ASSERT(!current_defn->HasUses());
       THR_Print("Removing v%" Pd ".\n", current_defn->ssa_temp_index());
     }
   }
   if (current->ArgumentCount() != 0) {
-    // This is a call instruction. Must remove original push arguments.
+    // Replacing a call instruction with something else.  Must remove
+    // superfluous push arguments.
     for (intptr_t i = 0; i < current->ArgumentCount(); ++i) {
       PushArgumentInstr* push = current->PushArgumentAt(i);
-      push->ReplaceUsesWith(push->value()->definition());
-      push->RemoveFromGraph();
+      if (replacement == NULL || i >= replacement->ArgumentCount() ||
+          replacement->PushArgumentAt(i) != push) {
+        push->ReplaceUsesWith(push->value()->definition());
+        push->RemoveFromGraph();
+      }
     }
   }
   iterator->RemoveCurrentFromGraph();
 }
 
 
 void FlowGraph::AddToDeferredPrefixes(
     ZoneGrowableArray<const LibraryPrefix*>* from) {
   ZoneGrowableArray<const LibraryPrefix*>* to = deferred_prefixes();
   for (intptr_t i = 0; i < from->length(); i++) {
@@ skipping 2173 matching lines @@
                                                 Representation rep,
                                                 intptr_t cid) {
   ExtractNthOutputInstr* extract =
       new (Z) ExtractNthOutputInstr(new (Z) Value(instr), index, rep, cid);
   instr->ReplaceUsesWith(extract);
   InsertAfter(instr, extract, NULL, FlowGraph::kValue);
 }
 
 
 }  // namespace dart