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..13bd5541f617e058b299638cbd34f433d69a6e7c 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -810,6 +810,8 @@ class HValue: public ZoneObject {
     // has processed this instruction.
     kIDefsProcessingDone,
     kHasNoObservableSideEffects,
+    // used during dead code elimination to indicate the instruction is live

[Jakob Kummerow, 2013/05/08 12:07:24]

nit: Our style guide demands that comments be proper sentences, beginning with a
capital letter and ending with appropriate punctuation.
This remark applies to most comments introduced in this CL.

[titzer, 2013/05/13 13:29:38]

Done.

+    kIsNotDead,

[Sven Panne, 2013/05/07 13:32:10]

I don't like negated things, especially when the uses are negated, too.
Something like kAlive or kReachable (choose some positive formulation) is
better.

http://www.refactoring.com/catalog/removeDoubleNegative.html

[titzer, 2013/05/13 13:29:38]

Done.

     kLastFlag = kIDefsProcessingDone
   };
 
@@ -1076,6 +1078,11 @@ class HValue: public ZoneObject {
     return HasNoUses() && !HasObservableSideEffects() && IsDeletable();
   }
 
+  // has side effects or otherwise cannot be dead code eliminated
+  bool IsNotDeletable() const {
+    return HasObservableSideEffects() || !IsDeletable();

[Sven Panne, 2013/05/07 13:32:10]

Hmmm, do we really need IsDead *and* IsNotDeletable? !IsNotDeletable is a part
of IsDead, BTW. Again, negated things are not nice, see above.

[titzer, 2013/05/13 13:29:38]

Done.

+  }
+
 #ifdef DEBUG
   virtual void Verify() = 0;
 #endif
@@ -2965,7 +2972,6 @@ 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 +3031,6 @@ 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 +3080,6 @@ 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_;
 };