Turn dead code elimination into a proper HPhase.

R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/18791002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15529 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-dce.cc

+// Copyright 2013 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "hydrogen-dce.h"
+#include "v8.h"
+
+namespace v8 {
+namespace internal {
+
+bool HDeadCodeEliminationPhase::MarkLive(HValue* ref, HValue* instr) {
+  if (instr->CheckFlag(HValue::kIsLive)) return false;
+  instr->SetFlag(HValue::kIsLive);
+
+  if (FLAG_trace_dead_code_elimination) {
+    HeapStringAllocator allocator;
+    StringStream stream(&allocator);
+    if (ref != NULL) {
+      ref->PrintTo(&stream);
+    } else {
+      stream.Add("root ");
+    }
+    stream.Add(" -> ");
+    instr->PrintTo(&stream);
+    PrintF("[MarkLive %s]\n", *stream.ToCString());
+  }
+
+  return true;
+}
+
+
+void HDeadCodeEliminationPhase::MarkLiveInstructions() {
+  ZoneList<HValue*> worklist(graph()->blocks()->length(), zone());
+
+  // Mark initial root instructions for dead code elimination.
+  for (int i = 0; i < graph()->blocks()->length(); ++i) {
+    HBasicBlock* block = graph()->blocks()->at(i);
+    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+      HInstruction* instr = it.Current();
+      if (instr->CannotBeEliminated() && MarkLive(NULL, instr)) {
+        worklist.Add(instr, zone());
+      }
+    }
+    for (int j = 0; j < block->phis()->length(); j++) {
+      HPhi* phi = block->phis()->at(j);
+      if (phi->CannotBeEliminated() && MarkLive(NULL, phi)) {
+        worklist.Add(phi, zone());
+      }
+    }
+  }
+
+  // Transitively mark all inputs of live instructions live.
+  while (!worklist.is_empty()) {
+    HValue* instr = worklist.RemoveLast();
+    for (int i = 0; i < instr->OperandCount(); ++i) {
+      if (MarkLive(instr, instr->OperandAt(i))) {
+        worklist.Add(instr->OperandAt(i), zone());
+      }
+    }
+  }
+}
+
+
+void HDeadCodeEliminationPhase::RemoveDeadInstructions() {
+  ZoneList<HPhi*> worklist(graph()->blocks()->length(), zone());
+
+  // Remove any instruction not marked kIsLive.
+  for (int i = 0; i < graph()->blocks()->length(); ++i) {
+    HBasicBlock* block = graph()->blocks()->at(i);
+    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+      HInstruction* instr = it.Current();
+      if (!instr->CheckFlag(HValue::kIsLive)) {
+        // Instruction has not been marked live; assume it is dead and remove.
+        // TODO(titzer): we don't remove constants because some special ones
+        // might be used by later phases and are assumed to be in the graph
+        if (!instr->IsConstant()) instr->DeleteAndReplaceWith(NULL);
+      } else {
+        // Clear the liveness flag to leave the graph clean for the next DCE.
+        instr->ClearFlag(HValue::kIsLive);
+      }
+    }
+    // Collect phis that are dead and remove them in the next pass.
+    for (int j = 0; j < block->phis()->length(); j++) {
+      HPhi* phi = block->phis()->at(j);
+      if (!phi->CheckFlag(HValue::kIsLive)) {
+        worklist.Add(phi, zone());
+      } else {
+        phi->ClearFlag(HValue::kIsLive);
+      }
+    }
+  }
+
+  // Process phis separately to avoid simultaneously mutating the phi list.
+  while (!worklist.is_empty()) {
+    HPhi* phi = worklist.RemoveLast();
+    HBasicBlock* block = phi->block();
+    phi->DeleteAndReplaceWith(NULL);
+    block->RecordDeletedPhi(phi->merged_index());
+  }
+}
+
+} }  // namespace v8::internal

src/hydrogen-dce.h

+// Copyright 2013 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_HYDROGEN_DCE_H_
+#define V8_HYDROGEN_DCE_H_
+
+#include "hydrogen.h"
+
+namespace v8 {
+namespace internal {
+
+
+class HDeadCodeEliminationPhase : public HPhase {
+ public:
+  explicit HDeadCodeEliminationPhase(HGraph* graph)
+      : HPhase("H_Dead code elimination", graph) { }
+
+  void Run() {
+    MarkLiveInstructions();
+    RemoveDeadInstructions();
+  }
+
+ private:
+  bool MarkLive(HValue* ref, HValue* instr);
+  void MarkLiveInstructions();
+  void RemoveDeadInstructions();
+};
+
+
+} }  // namespace v8::internal
+
+#endif  // V8_HYDROGEN_DCE_H_

src/hydrogen.cc

@@ -33,6 +33,7 @@
 #include "codegen.h"
 #include "full-codegen.h"
 #include "hashmap.h"
+#include "hydrogen-dce.h"
 #include "hydrogen-environment-liveness.h"
 #include "hydrogen-escape-analysis.h"
 #include "hydrogen-infer-representation.h"
@@ -3464,9 +3465,7 @@ bool HGraph::Optimize(SmartArrayPointer<char>* bailout_reason) {
   }
 
   // Remove dead code and phis
-  if (FLAG_dead_code_elimination) {
-    DeadCodeElimination("H_Eliminate early dead code");
-  }
+  if (FLAG_dead_code_elimination) Run<HDeadCodeEliminationPhase>();
   CollectPhis();
 
   if (has_osr()) osr()->FinishOsrValues();
@@ -3507,9 +3506,7 @@ bool HGraph::Optimize(SmartArrayPointer<char>* bailout_reason) {
     EliminateRedundantBoundsChecks();
   }
   if (FLAG_array_index_dehoisting) DehoistSimpleArrayIndexComputations();
-  if (FLAG_dead_code_elimination) {
-    DeadCodeElimination("H_Eliminate late dead code");
-  }
+  if (FLAG_dead_code_elimination) Run<HDeadCodeEliminationPhase>();
 
   RestoreActualValues();
 
@@ -3990,99 +3987,6 @@ void HGraph::DehoistSimpleArrayIndexComputations() {
 }
 
 
-void HGraph::DeadCodeElimination(const char* phase_name) {
-  HPhase phase(phase_name, this);
-  MarkLiveInstructions();
-  RemoveDeadInstructions();
-}
-
-
-void HGraph::MarkLiveInstructions() {
-  ZoneList<HValue*> worklist(blocks_.length(), zone());
-
-  // Mark initial root instructions for dead code elimination.
-  for (int i = 0; i < blocks()->length(); ++i) {
-    HBasicBlock* block = blocks()->at(i);
-    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
-      HInstruction* instr = it.Current();
-      if (instr->CannotBeEliminated()) MarkLive(NULL, instr, &worklist);
-    }
-    for (int j = 0; j < block->phis()->length(); j++) {
-      HPhi* phi = block->phis()->at(j);
-      if (phi->CannotBeEliminated()) MarkLive(NULL, phi, &worklist);
-    }
-  }
-
-  // Transitively mark all inputs of live instructions live.
-  while (!worklist.is_empty()) {
-    HValue* instr = worklist.RemoveLast();
-    for (int i = 0; i < instr->OperandCount(); ++i) {
-      MarkLive(instr, instr->OperandAt(i), &worklist);
-    }
-  }
-}
-
-
-void HGraph::MarkLive(HValue* ref, HValue* instr, ZoneList<HValue*>* worklist) {
-  if (!instr->CheckFlag(HValue::kIsLive)) {
-    instr->SetFlag(HValue::kIsLive);
-    worklist->Add(instr, zone());
-
-    if (FLAG_trace_dead_code_elimination) {
-      HeapStringAllocator allocator;
-      StringStream stream(&allocator);
-      if (ref != NULL) {
-        ref->PrintTo(&stream);
-      } else {
-        stream.Add("root ");
-      }
-      stream.Add(" -> ");
-      instr->PrintTo(&stream);
-      PrintF("[MarkLive %s]\n", *stream.ToCString());
-    }
-  }
-}
-
-
-void HGraph::RemoveDeadInstructions() {
-  ZoneList<HPhi*> dead_phis(blocks_.length(), zone());
-
-  // Remove any instruction not marked kIsLive.
-  for (int i = 0; i < blocks()->length(); ++i) {
-    HBasicBlock* block = blocks()->at(i);
-    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
-      HInstruction* instr = it.Current();
-      if (!instr->CheckFlag(HValue::kIsLive)) {
-        // Instruction has not been marked live; assume it is dead and remove.
-        // TODO(titzer): we don't remove constants because some special ones
-        // might be used by later phases and are assumed to be in the graph
-        if (!instr->IsConstant()) instr->DeleteAndReplaceWith(NULL);
-      } else {
-        // Clear the liveness flag to leave the graph clean for the next DCE.
-        instr->ClearFlag(HValue::kIsLive);
-      }
-    }
-    // Collect phis that are dead and remove them in the next pass.
-    for (int j = 0; j < block->phis()->length(); j++) {
-      HPhi* phi = block->phis()->at(j);
-      if (!phi->CheckFlag(HValue::kIsLive)) {
-        dead_phis.Add(phi, zone());
-      } else {
-        phi->ClearFlag(HValue::kIsLive);
-      }
-    }
-  }
-
-  // Process phis separately to avoid simultaneously mutating the phi list.
-  while (!dead_phis.is_empty()) {
-    HPhi* phi = dead_phis.RemoveLast();
-    HBasicBlock* block = phi->block();
-    phi->DeleteAndReplaceWith(NULL);
-    block->RecordDeletedPhi(phi->merged_index());
-  }
-}
-
-
 void HGraph::RestoreActualValues() {
   HPhase phase("H_Restore actual values", this);
 

src/hydrogen.h

@@ -306,7 +306,6 @@ class HGraph: public ZoneObject {
   void EliminateRedundantBoundsChecks();
   void DehoistSimpleArrayIndexComputations();
   void RestoreActualValues();
-  void DeadCodeElimination(const char *phase_name);
   void PropagateDeoptimizingMark();
   void AnalyzeAndPruneEnvironmentLiveness();
 
@@ -451,9 +450,6 @@ class HGraph: public ZoneObject {
     phase.Run();
   }
 
-  void MarkLive(HValue* ref, HValue* instr, ZoneList<HValue*>* worklist);
-  void MarkLiveInstructions();
-  void RemoveDeadInstructions();
   void MarkAsDeoptimizingRecursively(HBasicBlock* block);
   void NullifyUnreachableInstructions();
   void InsertTypeConversions(HInstruction* instr);

tools/gyp/v8.gyp

@@ -335,6 +335,8 @@
         '../../src/heap-snapshot-generator.h',
         '../../src/heap.cc',
         '../../src/heap.h',
+        '../../src/hydrogen-dce.cc',
+        '../../src/hydrogen-dce.h',
         '../../src/hydrogen-environment-liveness.cc',
         '../../src/hydrogen-environment-liveness.h',
         '../../src/hydrogen-escape-analysis.cc',