Detect truncating Phi uses of Phis with constant inputs

src/hydrogen-instructions.cc

 // Copyright 2012 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 1940 matching lines @@
 void HPhi::DeleteFromGraph() {
   ASSERT(block() != NULL);
   block()->RemovePhi(this);
   ASSERT(block() == NULL);
 }
 
 
 void HPhi::InitRealUses(int phi_id) {
   // Initialize real uses.
   phi_id_ = phi_id;
+  // Compute a conservative approximation of truncating uses before inferring
+  // representations. The proper, exact computation will be done later, when
+  // inserting representation changes.
+  SetFlag(kTruncatingToInt32);
   for (HUseIterator it(uses()); !it.Done(); it.Advance()) {
     HValue* value = it.value();
     if (!value->IsPhi()) {
       Representation rep = value->observed_input_representation(it.index());
       non_phi_uses_[rep.kind()] += value->LoopWeight();
       if (FLAG_trace_representation) {
         PrintF("#%d Phi is used by real #%d %s as %s\n",
                id(), value->id(), value->Mnemonic(), rep.Mnemonic());
       }
+      if (!value->IsSimulate() && !value->CheckFlag(kTruncatingToInt32)) {
+        ClearFlag(kTruncatingToInt32);
+      }
     }
   }
 }
 
 
 void HPhi::AddNonPhiUsesFrom(HPhi* other) {
   if (FLAG_trace_representation) {
     PrintF("adding to #%d Phi uses of #%d Phi: i%d d%d t%d\n",
            id(), other->id(),
            other->non_phi_uses_[Representation::kInteger32],
@@ skipping 1647 matching lines @@
 
 
 void HCheckFunction::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal