Simplify the check when to perform loop invariant code motion.

src/hydrogen.cc

 // Copyright 2011 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 50 matching lines @@
       loop_information_(NULL),
       predecessors_(2),
       dominator_(NULL),
       dominated_blocks_(4),
       last_environment_(NULL),
       argument_count_(-1),
       first_instruction_index_(-1),
       last_instruction_index_(-1),
       deleted_phis_(4),
       parent_loop_header_(NULL),
-      is_inline_return_target_(false) { }
+      is_inline_return_target_(false),
+      is_deoptimizing_(false) { }
 
 
 void HBasicBlock::AttachLoopInformation() {
   ASSERT(!IsLoopHeader());
   loop_information_ = new(zone()) HLoopInformation(this);
 }
 
 
 void HBasicBlock::DetachLoopInformation() {
   ASSERT(IsLoopHeader());
@@ skipping 1359 matching lines @@
 
 
 bool HGlobalValueNumberer::AllowCodeMotion() {
   return info()->shared_info()->opt_count() + 1 < Compiler::kDefaultMaxOptCount;
 }
 
 
 bool HGlobalValueNumberer::ShouldMove(HInstruction* instr,
                                       HBasicBlock* loop_header) {
   // If we've disabled code motion, don't move any instructions.
   if (!AllowCodeMotion()) return false;

[Kevin Millikin (Chromium), 2011/06/09 15:18:00]

return AllowCodeMotion() && !instr->block()->IsDeoptimizing();

[fschneider, 2011/06/09 15:46:47]

Done.

-
-  // If --aggressive-loop-invariant-motion, move everything except change
-  // instructions.
-  if (FLAG_aggressive_loop_invariant_motion && !instr->IsChange()) {
-    return true;
-  }
-
-  // Otherwise only move instructions that postdominate the loop header
-  // (i.e. are always executed inside the loop). This is to avoid
-  // unnecessary deoptimizations assuming the loop is executed at least
-  // once.  TODO(fschneider): Better type feedback should give us
-  // information about code that was never executed.
-  HBasicBlock* block = instr->block();
-  bool result = true;
-  if (block != loop_header) {
-    for (int i = 1; i < loop_header->predecessors()->length(); ++i) {
-      bool found = false;
-      HBasicBlock* pred = loop_header->predecessors()->at(i);
-      while (pred != loop_header) {
-        if (pred == block) found = true;
-        pred = pred->dominator();
-      }
-      if (!found) {
-        result = false;
-        break;
-      }
-    }
-  }
-  return result;
+  // Don't hoist code from never executed paths.
+  if (instr->block()->IsDeoptimizing()) return false;
+  return true;
 }
 
 
 int HGlobalValueNumberer::CollectSideEffectsOnPathsToDominatedBlock(
     HBasicBlock* dominator, HBasicBlock* dominated) {
   int side_effects = 0;
   for (int i = 0; i < dominated->predecessors()->length(); ++i) {
     HBasicBlock* block = dominated->predecessors()->at(i);
     if (dominator->block_id() < block->block_id() &&
         block->block_id() < dominated->block_id() &&
@@ skipping 3352 matching lines @@
 }
 
 
 void HGraphBuilder::VisitSub(UnaryOperation* expr) {
   CHECK_ALIVE(VisitForValue(expr->expression()));
   HValue* value = Pop();
   HInstruction* instr = new(zone()) HMul(value, graph_->GetConstantMinus1());
   TypeInfo info = oracle()->UnaryType(expr);
   if (info.IsUninitialized()) {
     AddInstruction(new(zone()) HSoftDeoptimize);
+    current_block()->MarkAsDeoptimizing();
     info = TypeInfo::Unknown();
   }
   Representation rep = ToRepresentation(info);
   TraceRepresentation(expr->op(), info, instr, rep);
   instr->AssumeRepresentation(rep);
   ast_context()->ReturnInstruction(instr, expr->id());
 }
 
 
 void HGraphBuilder::VisitBitNot(UnaryOperation* expr) {
   CHECK_ALIVE(VisitForValue(expr->expression()));
   HValue* value = Pop();
   TypeInfo info = oracle()->UnaryType(expr);
   if (info.IsUninitialized()) {
     AddInstruction(new(zone()) HSoftDeoptimize);
+    current_block()->MarkAsDeoptimizing();
   }
   HInstruction* instr = new(zone()) HBitNot(value);
   ast_context()->ReturnInstruction(instr, expr->id());
 }
 
 
 void HGraphBuilder::VisitNot(UnaryOperation* expr) {
   // TODO(svenpanne) Perhaps a switch/virtual function is nicer here.
   if (ast_context()->IsTest()) {
     TestContext* context = TestContext::cast(ast_context());
@@ skipping 215 matching lines @@
   return new(zone()) HStringCharCodeAt(string, checked_index);
 }
 
 
 HInstruction* HGraphBuilder::BuildBinaryOperation(BinaryOperation* expr,
                                                   HValue* left,
                                                   HValue* right) {
   TypeInfo info = oracle()->BinaryType(expr);
   if (info.IsUninitialized()) {
     AddInstruction(new(zone()) HSoftDeoptimize);
+    current_block()->MarkAsDeoptimizing();
     info = TypeInfo::Unknown();
   }
   HInstruction* instr = NULL;
   switch (expr->op()) {
     case Token::ADD:
       if (info.IsString()) {
         AddInstruction(new(zone()) HCheckNonSmi(left));
         AddInstruction(HCheckInstanceType::NewIsString(left));
         AddInstruction(new(zone()) HCheckNonSmi(right));
         AddInstruction(HCheckInstanceType::NewIsString(right));
@@ skipping 249 matching lines @@
         Handle<String>::cast(right_literal->handle()));
     instr->set_position(expr->position());
     ast_context()->ReturnInstruction(instr, expr->id());
     return;
   }
 
   TypeInfo type_info = oracle()->CompareType(expr);
   // Check if this expression was ever executed according to type feedback.
   if (type_info.IsUninitialized()) {
     AddInstruction(new(zone()) HSoftDeoptimize);
+    current_block()->MarkAsDeoptimizing();
     type_info = TypeInfo::Unknown();
   }
 
   CHECK_ALIVE(VisitForValue(expr->left()));
   CHECK_ALIVE(VisitForValue(expr->right()));
 
   HValue* right = Pop();
   HValue* left = Pop();
   Token::Value op = expr->op();
 
@@ skipping 1023 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal