Disable speculative LICM when it may lead to unnecessary deopts

src/hydrogen.cc

 // Copyright 2012 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 678 matching lines @@
 
 HGraph::HGraph(CompilationInfo* info)
     : isolate_(info->isolate()),
       next_block_id_(0),
       entry_block_(NULL),
       blocks_(8, info->zone()),
       values_(16, info->zone()),
       phi_list_(NULL),
       info_(info),
       zone_(info->zone()),
-      is_recursive_(false) {
+      is_recursive_(false),
+      use_optimistic_licm_(false),
+      type_change_checksum_(0) {
   start_environment_ =
       new(zone_) HEnvironment(NULL, info->scope(), info->closure(), zone_);
   start_environment_->set_ast_id(BailoutId::FunctionEntry());
   entry_block_ = CreateBasicBlock();
   entry_block_->SetInitialEnvironment(start_environment_);
 }
 
 
 HBasicBlock* HGraph::CreateBasicBlock() {
   HBasicBlock* result = new(zone()) HBasicBlock(this);
@@ skipping 1182 matching lines @@
 #endif
   size_t string_len = strlen(underlying_buffer) + 1;
   ASSERT(string_len <= sizeof(underlying_buffer));
   char* result = new char[strlen(underlying_buffer) + 1];
   memcpy(result, underlying_buffer, string_len);
   return SmartArrayPointer<char>(result);
 }
 
 
 void HGlobalValueNumberer::LoopInvariantCodeMotion() {
+  TRACE_GVN_1("Using optimistic loop invariant code motion: %s\n",
+              graph_->use_optimistic_licm() ? "yes" : "no");
   for (int i = graph_->blocks()->length() - 1; i >= 0; --i) {
     HBasicBlock* block = graph_->blocks()->at(i);
     if (block->IsLoopHeader()) {
       GVNFlagSet side_effects = loop_side_effects_[block->block_id()];
       TRACE_GVN_2("Try loop invariant motion for block B%d %s\n",
                   block->block_id(),
                   *GetGVNFlagsString(side_effects));
 
       GVNFlagSet accumulated_first_time_depends;
       GVNFlagSet accumulated_first_time_changes;
@@ skipping 23 matching lines @@
   while (instr != NULL) {
     HInstruction* next = instr->next();
     bool hoisted = false;
     if (instr->CheckFlag(HValue::kUseGVN)) {
       TRACE_GVN_4("Checking instruction %d (%s) %s. Loop %s\n",
                   instr->id(),
                   instr->Mnemonic(),
                   *GetGVNFlagsString(instr->gvn_flags()),
                   *GetGVNFlagsString(loop_kills));
       bool can_hoist = !instr->gvn_flags().ContainsAnyOf(depends_flags);
+      if (can_hoist && !graph()->use_optimistic_licm()) {
+        can_hoist = block->IsLoopSuccessorDominator();
+      }
       if (instr->IsTransitionElementsKind()) {
         // It's possible to hoist transitions out of a loop as long as the
         // hoisting wouldn't move the transition past an instruction that has a
         // DependsOn flag for anything it changes.
         GVNFlagSet hoist_depends_blockers =
             HValue::ConvertChangesToDependsFlags(instr->ChangesFlags());
 
         // In addition, the transition must not be hoisted above elements kind
         // changes, or if the transition is destructive to the elements buffer,
         // changes to array pointer or array contents.
@@ skipping 1124 matching lines @@
         new(zone()) HStackCheck(context, HStackCheck::kFunctionEntry));
 
     VisitStatements(info()->function()->body());
     if (HasStackOverflow()) return NULL;
 
     if (current_block() != NULL) {
       HReturn* instr = new(zone()) HReturn(graph()->GetConstantUndefined());
       current_block()->FinishExit(instr);
       set_current_block(NULL);
     }
+
+    // If the checksum of the number of type info changes is the same as the
+    // last time this function was compiled, then this recompile is likely not
+    // due to missing/inadequate type feedback, but rather too aggressive
+    // optimization. Disable optimistic LICM in that case.
+    Handle<Code> unoptimized_code(info()->shared_info()->code());
+    ASSERT(unoptimized_code->kind() == Code::FUNCTION);
+    Handle<Object> maybe_type_info(unoptimized_code->type_feedback_info());
+    Handle<TypeFeedbackInfo> type_info(
+        Handle<TypeFeedbackInfo>::cast(maybe_type_info));
+    int checksum = type_info->own_type_change_checksum();
+    int composite_checksum = graph()->update_type_change_checksum(checksum);
+    graph()->set_use_optimistic_licm(
+        !type_info->matches_inlined_type_change_checksum(composite_checksum));
+    type_info->set_inlined_type_change_checksum(composite_checksum);
   }
 
   return graph();
 }
 
 bool HGraph::Optimize(SmartArrayPointer<char>* bailout_reason) {
   *bailout_reason = SmartArrayPointer<char>();
   OrderBlocks();
   AssignDominators();
 
@@ skipping 3715 matching lines @@
                                         target_shared);
   }
 
   // ----------------------------------------------------------------
   // After this point, we've made a decision to inline this function (so
   // TryInline should always return true).
 
   // Save the pending call context and type feedback oracle. Set up new ones
   // for the inlined function.
   ASSERT(target_shared->has_deoptimization_support());
+  Handle<Code> unoptimized_code(target_shared->code());
   TypeFeedbackOracle target_oracle(
-      Handle<Code>(target_shared->code()),
+      unoptimized_code,
       Handle<Context>(target->context()->native_context()),
       isolate(),
       zone());
   // The function state is new-allocated because we need to delete it
   // in two different places.
   FunctionState* target_state = new FunctionState(
       this, &target_info, &target_oracle, inlining_kind);
 
   HConstant* undefined = graph()->GetConstantUndefined();
   HEnvironment* inner_env =
@@ skipping 59 matching lines @@
     TraceInline(target, caller, "inline graph construction failed");
     target_shared->DisableOptimization();
     inline_bailout_ = true;
     delete target_state;
     return true;
   }
 
   // Update inlined nodes count.
   inlined_count_ += nodes_added;
 
+  ASSERT(unoptimized_code->kind() == Code::FUNCTION);
+  Handle<Object> maybe_type_info(unoptimized_code->type_feedback_info());
+  Handle<TypeFeedbackInfo> type_info(
+      Handle<TypeFeedbackInfo>::cast(maybe_type_info));
+  graph()->update_type_change_checksum(type_info->own_type_change_checksum());
+
   TraceInline(target, caller, NULL);
 
   if (current_block() != NULL) {
     FunctionState* state = function_state();
     if (state->inlining_kind() == CONSTRUCT_CALL_RETURN) {
       // Falling off the end of an inlined construct call. In a test context the
       // return value will always evaluate to true, in a value context the
       // return value is the newly allocated receiver.
       if (call_context()->IsTest()) {
         current_block()->Goto(inlined_test_context()->if_true(), state);
@@ skipping 2782 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal