Refactored HInferRepresenation::TryChange a bit, making the heuristics a bit clearer.

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1631 matching lines @@
     if (rep.IsNone()) continue;
     if (use->IsPhi()) HPhi::cast(use)->AddIndirectUsesTo(&use_count[0]);
     ++use_count[rep.kind()];
   }
   int tagged_count = use_count[Representation::kTagged];
   int double_count = use_count[Representation::kDouble];
   int int32_count = use_count[Representation::kInteger32];
   int non_tagged_count = double_count + int32_count;
 
   // If a non-loop phi has tagged uses, don't convert it to untagged.
-  if (value->IsPhi() && !value->block()->IsLoopHeader()) {
-    if (tagged_count > 0) return Representation::None();
+  if (value->IsPhi() && !value->block()->IsLoopHeader() && tagged_count > 0) {
+    return Representation::None();
   }
 
-  if (non_tagged_count >= tagged_count) {
-    if (int32_count > 0) {
-      if (!value->IsPhi() || value->IsConvertibleToInteger()) {
-        return Representation::Integer32();
-      }
-    }
-    if (double_count > 0) return Representation::Double();
+  // Prefer unboxing over boxing, the latter is more expensive.
+  if (tagged_count > non_tagged_count) Representation::None();
+
+  // Prefer Integer32 over Double, if possible.
+  if (int32_count > 0 && value->IsConvertibleToInteger()) {
+    return Representation::Integer32();
   }
+
+  if (double_count > 0) return Representation::Double();
+
   return Representation::None();
 }
 
 
 void HInferRepresentation::Analyze() {
   HPhase phase("Infer representations", graph_);
 
   // (1) Initialize bit vectors and count real uses. Each phi gets a
   // bit-vector of length <number of phis>.
   const ZoneList<HPhi*>* phi_list = graph_->phi_list();
@@ skipping 5149 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal