Reduce impact of HParameter inputs on HPhi representation selection

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/base/bits.h"
 #include "src/double.h"
 #include "src/factory.h"
 #include "src/hydrogen-infer-representation.h"
@@ skipping 4479 matching lines @@
     if (use->IsBinaryOperation()) {
       HBinaryOperation::cast(use)->set_observed_input_representation(
           it.index(), Representation::Smi());
     }
   }
 }
 
 
 void HPhi::InferRepresentation(HInferRepresentationPhase* h_infer) {
   DCHECK(CheckFlag(kFlexibleRepresentation));
-  Representation new_rep = RepresentationFromInputs();
+  Representation new_rep = RepresentationFromUses();
+  UpdateRepresentation(new_rep, h_infer, "uses");
+  new_rep = RepresentationFromInputs();
   UpdateRepresentation(new_rep, h_infer, "inputs");
-  new_rep = RepresentationFromUses();
-  UpdateRepresentation(new_rep, h_infer, "uses");
   new_rep = RepresentationFromUseRequirements();
   UpdateRepresentation(new_rep, h_infer, "use requirements");
 }
 
 
 Representation HPhi::RepresentationFromInputs() {
-  Representation r = Representation::None();
+  bool has_type_feedback =
+      smi_non_phi_uses() + int32_non_phi_uses() + double_non_phi_uses() > 0;
+  Representation r = representation();
   for (int i = 0; i < OperandCount(); ++i) {
+    // Ignore conservative Tagged assumption of parameters if we have
+    // reason to believe that it's too conservative.
+    if (has_type_feedback && OperandAt(i)->IsParameter()) continue;
+
     r = r.generalize(OperandAt(i)->KnownOptimalRepresentation());
   }
   return r;
 }
 
 
 // Returns a representation if all uses agree on the same representation.
 // Integer32 is also returned when some uses are Smi but others are Integer32.
 Representation HValue::RepresentationFromUseRequirements() {
   Representation rep = Representation::None();
@@ skipping 283 matching lines @@
       break;
     case HObjectAccess::kExternalMemory:
       os << "[external-memory]";
       break;
   }
 
   return os << "@" << access.offset();
 }
 
 } }  // namespace v8::internal