Improve and simplify removal of unreachable code

src/hydrogen-gvn.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
@@ skipping 378 matching lines @@
 void HGlobalValueNumberingPhase::ComputeBlockSideEffects() {
   // The Analyze phase of GVN can be called multiple times. Clear loop side
   // effects before computing them to erase the contents from previous Analyze
   // passes.
   for (int i = 0; i < loop_side_effects_.length(); ++i) {
     loop_side_effects_[i].RemoveAll();
   }
   for (int i = graph()->blocks()->length() - 1; i >= 0; --i) {
     // Compute side effects for the block.
     HBasicBlock* block = graph()->blocks()->at(i);
-    int id = block->block_id();
     GVNFlagSet side_effects;
-    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
-      HInstruction* instr = it.Current();
-      side_effects.Add(instr->ChangesFlags());
-      if (instr->IsDeoptimize()) {
-        block_side_effects_[id].RemoveAll();
-        side_effects.RemoveAll();
-        break;
+    if (block->IsReachable() && !block->IsDeoptimizing()) {
+      int id = block->block_id();
+      for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+        HInstruction* instr = it.Current();
+        side_effects.Add(instr->ChangesFlags());
       }
-    }
-    block_side_effects_[id].Add(side_effects);
+      block_side_effects_[id].Add(side_effects);
 
-    // Loop headers are part of their loop.
-    if (block->IsLoopHeader()) {
-      loop_side_effects_[id].Add(side_effects);
-    }
+      // Loop headers are part of their loop.
+      if (block->IsLoopHeader()) {
+        loop_side_effects_[id].Add(side_effects);
+      }
 
-    // Propagate loop side effects upwards.
-    if (block->HasParentLoopHeader()) {
-      int header_id = block->parent_loop_header()->block_id();
-      loop_side_effects_[header_id].Add(block->IsLoopHeader()
-                                        ? loop_side_effects_[id]
-                                        : side_effects);
+      // Propagate loop side effects upwards.
+      if (block->HasParentLoopHeader()) {
+        int header_id = block->parent_loop_header()->block_id();
+        loop_side_effects_[header_id].Add(block->IsLoopHeader()
+                                          ? loop_side_effects_[id]
+                                          : side_effects);
+      }
     }
   }
 }
 
 
 SmartArrayPointer<char> GetGVNFlagsString(GVNFlagSet flags) {
   char underlying_buffer[kLastFlag * 128];
   Vector<char> buffer(underlying_buffer, sizeof(underlying_buffer));
 #if DEBUG
   int offset = 0;
@@ skipping 169 matching lines @@
 
 bool HGlobalValueNumberingPhase::AllowCodeMotion() {
   return info()->IsStub() || info()->opt_count() + 1 < FLAG_max_opt_count;
 }
 
 
 bool HGlobalValueNumberingPhase::ShouldMove(HInstruction* instr,
                                             HBasicBlock* loop_header) {
   // If we've disabled code motion or we're in a block that unconditionally
   // deoptimizes, don't move any instructions.
-  return AllowCodeMotion() && !instr->block()->IsDeoptimizing();
+  return AllowCodeMotion() && !instr->block()->IsDeoptimizing() &&
+      instr->block()->IsReachable();
 }
 
 
 GVNFlagSet
 HGlobalValueNumberingPhase::CollectSideEffectsOnPathsToDominatedBlock(
     HBasicBlock* dominator, HBasicBlock* dominated) {
   GVNFlagSet side_effects;
   for (int i = 0; i < dominated->predecessors()->length(); ++i) {
     HBasicBlock* block = dominated->predecessors()->at(i);
     if (dominator->block_id() < block->block_id() &&
@@ skipping 223 matching lines @@
                                                       dominated);
         successor_map->Kill(side_effects_on_all_paths);
         successor_dominators->Kill(side_effects_on_all_paths);
       }
     }
     current = next;
   }
 }
 
 } }  // namespace v8::internal