Perform a fix point iteration for GVN.

BUG=
R=danno@chromium.org

Review URL: https://codereview.chromium.org/149573014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19115 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -247,6 +247,7 @@ DEFINE_bool(crankshaft, true, "use crankshaft")
 DEFINE_string(hydrogen_filter, "*", "optimization filter")
 DEFINE_bool(use_range, true, "use hydrogen range analysis")
 DEFINE_bool(use_gvn, true, "use hydrogen global value numbering")
+DEFINE_int(gvn_iterations, 3, "maximum number of GVN fix-point iterations")
 DEFINE_bool(use_canonicalizing, true, "use hydrogen instruction canonicalizing")
 DEFINE_bool(use_inlining, true, "use function inlining")
 DEFINE_bool(use_escape_analysis, true, "use hydrogen escape analysis")

src/hydrogen-gvn.cc

@@ -374,7 +374,19 @@ HGlobalValueNumberingPhase::HGlobalValueNumberingPhase(HGraph* graph)
                                  zone());
     loop_side_effects_.AddBlock(GVNFlagSet(), graph->blocks()->length(),
                                 zone());
-  }
+}
+
+
+void HGlobalValueNumberingPhase::Reset() {
+  block_side_effects_.Clear();
+  loop_side_effects_.Clear();
+  visited_on_paths_.Clear();
+  block_side_effects_.AddBlock(GVNFlagSet(), graph()->blocks()->length(),
+                               zone());
+  loop_side_effects_.AddBlock(GVNFlagSet(), graph()->blocks()->length(),
+                              zone());
+}
+
 
 void HGlobalValueNumberingPhase::Analyze() {
   removed_side_effects_ = false;
@@ -791,7 +803,9 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
                         instr->Mnemonic(),
                         other->id(),
                         other->Mnemonic());
-            instr->HandleSideEffectDominator(changes_flag, other);
+            if (instr->HandleSideEffectDominator(changes_flag, other)) {
+              removed_side_effects_ = true;
+            }
           }
         }
       }

src/hydrogen-gvn.h

@@ -42,17 +42,16 @@ class HGlobalValueNumberingPhase : public HPhase {
   explicit HGlobalValueNumberingPhase(HGraph* graph);
 
   void Run() {
-    Analyze();
-    // Trigger a second analysis pass to further eliminate duplicate values
-    // that could only be discovered by removing side-effect-generating
-    // instructions during the first pass.
-    if (FLAG_smi_only_arrays && removed_side_effects_) {
+    int max_fixpoint_iteration_count = FLAG_gvn_iterations;
+    for (int i = 0; i < max_fixpoint_iteration_count; i++) {
       Analyze();
-      // TODO(danno): Turn this into a fixpoint iteration.
+      if (!removed_side_effects_) break;
+      Reset();
     }
   }
 
  private:
+  void Reset();
   void Analyze();
   GVNFlagSet CollectSideEffectsOnPathsToDominatedBlock(
       HBasicBlock* dominator,

src/hydrogen-instructions.cc

@@ -1514,7 +1514,7 @@ void HCheckInstanceType::GetCheckMaskAndTag(uint8_t* mask, uint8_t* tag) {
 }
 
 
-void HCheckMaps::HandleSideEffectDominator(GVNFlag side_effect,
+bool HCheckMaps::HandleSideEffectDominator(GVNFlag side_effect,
                                            HValue* dominator) {
   ASSERT(side_effect == kChangesMaps);
   // TODO(mstarzinger): For now we specialize on HStoreNamedField, but once
@@ -1522,13 +1522,14 @@ void HCheckMaps::HandleSideEffectDominator(GVNFlag side_effect,
   // for which the map is known.
   if (HasNoUses() && dominator->IsStoreNamedField()) {
     HStoreNamedField* store = HStoreNamedField::cast(dominator);
-    if (!store->has_transition() || store->object() != value()) return;
+    if (!store->has_transition() || store->object() != value()) return false;
     HConstant* transition = HConstant::cast(store->transition());
     if (map_set_.Contains(transition->GetUnique())) {
       DeleteAndReplaceWith(NULL);
-      return;
+      return true;
     }
   }
+  return false;
 }
 
 
@@ -3409,11 +3410,11 @@ Representation HUnaryMathOperation::RepresentationFromInputs() {
 }
 
 
-void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
+bool HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
                                           HValue* dominator) {
   ASSERT(side_effect == kChangesNewSpacePromotion);
   Zone* zone = block()->zone();
-  if (!FLAG_use_allocation_folding) return;
+  if (!FLAG_use_allocation_folding) return false;
 
   // Try to fold allocations together with their dominating allocations.
   if (!dominator->IsAllocate()) {
@@ -3421,7 +3422,7 @@ void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
       PrintF("#%d (%s) cannot fold into #%d (%s)\n",
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
-    return;
+    return false;
   }
 
   HAllocate* dominator_allocate = HAllocate::cast(dominator);
@@ -3435,12 +3436,12 @@ void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
       PrintF("#%d (%s) cannot fold into #%d (%s), dynamic allocation size\n",
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
-    return;
+    return false;
   }
 
   dominator_allocate = GetFoldableDominator(dominator_allocate);
   if (dominator_allocate == NULL) {
-    return;
+    return false;
   }
 
   ASSERT((IsNewSpaceAllocation() &&
@@ -3477,7 +3478,7 @@ void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
           id(), Mnemonic(), dominator_allocate->id(),
           dominator_allocate->Mnemonic(), new_dominator_size);
     }
-    return;
+    return false;
   }
 
   HInstruction* new_dominator_size_constant = HConstant::CreateAndInsertBefore(
@@ -3525,6 +3526,7 @@ void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
         id(), Mnemonic(), dominator_allocate->id(),
         dominator_allocate->Mnemonic());
   }
+  return true;
 }
 
 

src/hydrogen-instructions.h

@@ -875,9 +875,11 @@ class HValue : public ZoneObject {
   // This function must be overridden for instructions which have the
   // kTrackSideEffectDominators flag set, to track instructions that are
   // dominating side effects.
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  // It returns true if it removed an instruction which had side effects.
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) {
     UNREACHABLE();
+    return false;
   }
 
   // Check if this instruction has some reason that prevents elimination.
@@ -2680,7 +2682,7 @@ class HCheckMaps V8_FINAL : public HTemplateInstruction<2> {
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::Tagged();
   }
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE;
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
@@ -5349,7 +5351,7 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
     flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATE_DOUBLE_ALIGNED);
   }
 
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE;
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
@@ -6461,10 +6463,11 @@ class HStoreNamedField V8_FINAL : public HTemplateInstruction<3> {
     }
     return Representation::Tagged();
   }
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE {
     ASSERT(side_effect == kChangesNewSpacePromotion);
     new_space_dominator_ = dominator;
+    return false;
   }
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
@@ -6691,10 +6694,11 @@ class HStoreKeyed V8_FINAL
     return value()->IsConstant() && HConstant::cast(value())->IsTheHole();
   }
 
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE {
     ASSERT(side_effect == kChangesNewSpacePromotion);
     new_space_dominator_ = dominator;
+    return false;
   }
 
   HValue* new_space_dominator() const { return new_space_dominator_; }