Base iDef update code.

Review URL: https://codereview.chromium.org/12079042

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13575 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -205,6 +205,7 @@ DEFINE_bool(trap_on_deopt, false, "put a break point before deoptimizing")
 DEFINE_bool(deoptimize_uncommon_cases, true, "deoptimize uncommon cases")
 DEFINE_bool(polymorphic_inlining, true, "polymorphic inlining")
 DEFINE_bool(use_osr, true, "use on-stack replacement")
+DEFINE_bool(idefs, false, "use informative definitions")
 DEFINE_bool(array_bounds_checks_elimination, true,
             "perform array bounds checks elimination")
 DEFINE_bool(array_index_dehoisting, true,

src/hydrogen-instructions.cc

@@ -364,6 +364,54 @@ HType HType::TypeFromValue(Handle<Object> value) {
 }
 
 
+bool HValue::Dominates(HValue* dominator, HValue* dominated) {
+  if (dominator->block() != dominated->block()) {
+    // If they are in different blocks we can use the dominance relation
+    // between the blocks.
+    return dominator->block()->Dominates(dominated->block());
+  } else {
+    // Otherwise we must see which instruction comes first, considering
+    // that phis always precede regular instructions.
+    if (dominator->IsInstruction()) {
+      if (dominated->IsInstruction()) {
+        for (HInstruction* next = HInstruction::cast(dominator)->next();
+             next != NULL;
+             next = next->next()) {
+          if (next == dominated) return true;
+        }
+        return false;
+      } else if (dominated->IsPhi()) {
+        return false;
+      } else {
+        UNREACHABLE();
+      }
+    } else if (dominator->IsPhi()) {
+      if (dominated->IsInstruction()) {
+        return true;
+      } else {
+        // We cannot compare which phi comes first.
+        UNREACHABLE();
+      }
+    } else {
+      UNREACHABLE();
+    }
+    return false;
+  }
+}
+
+
+bool HValue::TestDominanceUsingProcessedFlag(HValue* dominator,
+                                             HValue* dominated) {
+  if (dominator->block() != dominated->block()) {
+    return dominator->block()->Dominates(dominated->block());
+  } else {
+    // If both arguments are in the same block we check if "dominator" has
+    // already been processed or if it is a phi: if yes it dominates the other.
+    return dominator->CheckFlag(kIDefsProcessingDone) || dominator->IsPhi();
+  }
+}
+
+
 bool HValue::IsDefinedAfter(HBasicBlock* other) const {
   return block()->block_id() > other->block_id();
 }

src/hydrogen-instructions.h

@@ -579,7 +579,10 @@ class HValue: public ZoneObject {
     // HGraph::ComputeSafeUint32Operations is responsible for setting this
     // flag.
     kUint32,
-    kLastFlag = kUint32
+    // This flag is set to true after the SetupInformativeDefinitions() pass
+    // has processed this instruction.
+    kIDefsProcessingDone,
+    kLastFlag = kIDefsProcessingDone
   };
 
   STATIC_ASSERT(kLastFlag < kBitsPerInt);
@@ -687,8 +690,8 @@ class HValue: public ZoneObject {
     return RedefinedOperandIndex() != kNoRedefinedOperand;
   }
   HValue* RedefinedOperand() {
-    ASSERT(IsInformativeDefinition());
-    return OperandAt(RedefinedOperandIndex());
+    return IsInformativeDefinition() ? OperandAt(RedefinedOperandIndex())
+                                     : NULL;
   }
 
   // This method must always return the original HValue SSA definition
@@ -698,6 +701,15 @@ class HValue: public ZoneObject {
                                      : this;
   }
 
+  virtual void AddInformativeDefinitions() {}
+
+  void UpdateRedefinedUsesWhileSettingUpInformativeDefinitions() {
+    UpdateRedefinedUsesInner<TestDominanceUsingProcessedFlag>();
+  }
+  void UpdateRedefinedUses() {
+    UpdateRedefinedUsesInner<Dominates>();
+  }
+
   bool IsDefinedAfter(HBasicBlock* other) const;
 
   // Operands.
@@ -856,6 +868,36 @@ class HValue: public ZoneObject {
     representation_ = r;
   }
 
+  // Signature of a function testing if a HValue properly dominates another.
+  typedef bool (*DominanceTest)(HValue*, HValue*);
+
+  // Simple implementation of DominanceTest implemented walking the chain
+  // of Hinstructions (used in UpdateRedefinedUsesInner).
+  static bool Dominates(HValue* dominator, HValue* dominated);
+
+  // A fast implementation of DominanceTest that works only for the
+  // "current" instruction in the SetupInformativeDefinitions() phase.
+  // During that phase we use a flag to mark processed instructions, and by
+  // checking the flag we can quickly test if an instruction comes before or
+  // after the "current" one.
+  static bool TestDominanceUsingProcessedFlag(HValue* dominator,
+                                              HValue* dominated);
+
+  // If we are redefining an operand, update all its dominated uses (the
+  // function that checks if a use is dominated is the template argument).
+  template<DominanceTest TestDominance>
+  void UpdateRedefinedUsesInner() {
+    HValue* input = RedefinedOperand();
+    if (input != NULL) {
+      for (HUseIterator uses = input->uses(); !uses.Done(); uses.Advance()) {
+        HValue* use = uses.value();
+        if (TestDominance(this, use)) {
+          use->SetOperandAt(uses.index(), this);
+        }
+      }
+    }
+  }
+
   static GVNFlagSet AllDependsOnFlagSet() {
     GVNFlagSet result;
     // Create changes mask.

src/hydrogen.cc

@@ -3587,7 +3587,10 @@ bool HGraph::Optimize(SmartArrayPointer<char>* bailout_reason) {
   HStackCheckEliminator sce(this);
   sce.Process();
 
-  if (FLAG_array_bounds_checks_elimination) EliminateRedundantBoundsChecks();
+  if (FLAG_idefs) SetupInformativeDefinitions();
+  if (FLAG_array_bounds_checks_elimination && !FLAG_idefs) {
+    EliminateRedundantBoundsChecks();
+  }
   if (FLAG_array_index_dehoisting) DehoistSimpleArrayIndexComputations();
   if (FLAG_dead_code_elimination) DeadCodeElimination();
 
@@ -3597,6 +3600,39 @@ bool HGraph::Optimize(SmartArrayPointer<char>* bailout_reason) {
 }
 
 
+void HGraph::SetupInformativeDefinitionsInBlock(HBasicBlock* block) {
+  for (int phi_index = 0; phi_index < block->phis()->length(); phi_index++) {
+    HPhi* phi = block->phis()->at(phi_index);
+    phi->AddInformativeDefinitions();
+    // We do not support phis that "redefine just one operand".
+    ASSERT(!phi->IsInformativeDefinition());
+  }
+
+  for (HInstruction* i = block->first(); i != NULL; i = i->next()) {
+    i->AddInformativeDefinitions();
+    i->UpdateRedefinedUsesWhileSettingUpInformativeDefinitions();
+  }
+}
+
+
+// This method is recursive, so if its stack frame is large it could
+// cause a stack overflow.
+// To keep the individual stack frames small we do the actual work inside
+// SetupInformativeDefinitionsInBlock();
+void HGraph::SetupInformativeDefinitionsRecursively(HBasicBlock* block) {
+  SetupInformativeDefinitionsInBlock(block);
+  for (int i = 0; i < block->dominated_blocks()->length(); ++i) {
+    SetupInformativeDefinitionsRecursively(block->dominated_blocks()->at(i));
+  }
+}
+
+
+void HGraph::SetupInformativeDefinitions() {
+  HPhase phase("H_Setup informative definitions", this);
+  SetupInformativeDefinitionsRecursively(entry_block());
+}
+
+
 // We try to "factor up" HBoundsCheck instructions towards the root of the
 // dominator tree.
 // For now we handle checks where the index is like "exp + int32value".

src/hydrogen.h

@@ -269,7 +269,7 @@ class HGraph: public ZoneObject {
   void Canonicalize();
   void OrderBlocks();
   void AssignDominators();
-  void ReplaceCheckedValues();
+  void SetupInformativeDefinitions();
   void EliminateRedundantBoundsChecks();
   void DehoistSimpleArrayIndexComputations();
   void DeadCodeElimination();
@@ -398,6 +398,8 @@ class HGraph: public ZoneObject {
   void InferTypes(ZoneList<HValue*>* worklist);
   void InitializeInferredTypes(int from_inclusive, int to_inclusive);
   void CheckForBackEdge(HBasicBlock* block, HBasicBlock* successor);
+  void SetupInformativeDefinitionsInBlock(HBasicBlock* block);
+  void SetupInformativeDefinitionsRecursively(HBasicBlock* block);
   void EliminateRedundantBoundsChecks(HBasicBlock* bb, BoundsCheckTable* table);
 
   Isolate* isolate_;