Improve dead code elimination by transitively marking live code and removing all dead code. Replace…

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index decc62705b28808de6ca0f78b66fc503421dbc5e..a739f603e67958d68ec4e95e5b9bc60e6b4c30a7 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -795,6 +795,7 @@ class HValue: public ZoneObject {
     kDeoptimizeOnUndefined,
     kIsArguments,
     kTruncatingToInt32,
+    // Set after an instruction is killed.
     kIsDead,
     // Instructions that are allowed to produce full range unsigned integer
     // values are marked with kUint32 flag. If arithmetic shift or a load from
@@ -810,6 +811,8 @@ class HValue: public ZoneObject {
     // has processed this instruction.
     kIDefsProcessingDone,
     kHasNoObservableSideEffects,
+    // Indicates the instruction is live during dead code elimination.
+    kIsLive,
     kLastFlag = kIDefsProcessingDone
   };
 
@@ -1072,8 +1075,9 @@ class HValue: public ZoneObject {
     UNREACHABLE();
   }
 
-  bool IsDead() const {
-    return HasNoUses() && !HasObservableSideEffects() && IsDeletable();
+  // Check if this instruction has some reason that prevents elimination.
+  bool CanBeEliminated() const {
+    return !HasObservableSideEffects() && IsDeletable();
   }
 
 #ifdef DEBUG
@@ -2965,7 +2969,6 @@ class HPhi: public HValue {
       : inputs_(2, zone),
         merged_index_(merged_index),
         phi_id_(-1),
-        is_live_(false),
         is_convertible_to_integer_(true) {
     for (int i = 0; i < Representation::kNumRepresentations; i++) {
       non_phi_uses_[i] = 0;
@@ -3025,8 +3028,6 @@ class HPhi: public HValue {
     return indirect_uses_[Representation::kDouble];
   }
   int phi_id() { return phi_id_; }
-  bool is_live() { return is_live_; }
-  void set_is_live(bool b) { is_live_ = b; }
 
   static HPhi* cast(HValue* value) {
     ASSERT(value->IsPhi());
@@ -3076,7 +3077,6 @@ class HPhi: public HValue {
   int non_phi_uses_[Representation::kNumRepresentations];
   int indirect_uses_[Representation::kNumRepresentations];
   int phi_id_;
-  bool is_live_;
   bool is_convertible_to_integer_;
 };