LCOV - code coverage report
Current view: top level - src/compiler - dead-code-elimination.cc (source / functions) Hit Total Coverage
Test: app.info Lines: 156 156 100.0 %
Date: 2019-02-19 Functions: 20 20 100.0 %

          Line data    Source code
       1             : // Copyright 2015 the V8 project authors. All rights reserved.
       2             : // Use of this source code is governed by a BSD-style license that can be
       3             : // found in the LICENSE file.
       4             : 
       5             : #include "src/compiler/dead-code-elimination.h"
       6             : 
       7             : #include "src/compiler/common-operator.h"
       8             : #include "src/compiler/graph.h"
       9             : #include "src/compiler/js-operator.h"
      10             : #include "src/compiler/node-properties.h"
      11             : #include "src/compiler/operator-properties.h"
      12             : 
      13             : namespace v8 {
      14             : namespace internal {
      15             : namespace compiler {
      16             : 
      17     2815042 : DeadCodeElimination::DeadCodeElimination(Editor* editor, Graph* graph,
      18             :                                          CommonOperatorBuilder* common,
      19             :                                          Zone* temp_zone)
      20             :     : AdvancedReducer(editor),
      21             :       graph_(graph),
      22             :       common_(common),
      23     2815042 :       dead_(graph->NewNode(common->Dead())),
      24     5630097 :       zone_(temp_zone) {
      25             :   NodeProperties::SetType(dead_, Type::None());
      26     2815055 : }
      27             : 
      28             : namespace {
      29             : 
      30             : // True if we can guarantee that {node} will never actually produce a value or
      31             : // effect.
      32   814896980 : bool NoReturn(Node* node) {
      33   814845983 :   return node->opcode() == IrOpcode::kDead ||
      34   814846875 :          node->opcode() == IrOpcode::kUnreachable ||
      35  1629688235 :          node->opcode() == IrOpcode::kDeadValue ||
      36  1629688235 :          NodeProperties::GetTypeOrAny(node).IsNone();
      37             : }
      38             : 
      39   258496478 : Node* FindDeadInput(Node* node) {
      40  1331789212 :   for (Node* input : node->inputs()) {
      41   814896377 :     if (NoReturn(input)) return input;
      42             :   }
      43             :   return nullptr;
      44             : }
      45             : 
      46             : }  // namespace
      47             : 
      48   315421192 : Reduction DeadCodeElimination::Reduce(Node* node) {
      49             :   DisallowHeapAccess no_heap_access;
      50   315421192 :   switch (node->opcode()) {
      51             :     case IrOpcode::kEnd:
      52     3018038 :       return ReduceEnd(node);
      53             :     case IrOpcode::kLoop:
      54             :     case IrOpcode::kMerge:
      55     7800663 :       return ReduceLoopOrMerge(node);
      56             :     case IrOpcode::kLoopExit:
      57      344176 :       return ReduceLoopExit(node);
      58             :     case IrOpcode::kUnreachable:
      59             :     case IrOpcode::kIfException:
      60     2195315 :       return ReduceUnreachableOrIfException(node);
      61             :     case IrOpcode::kPhi:
      62     4149075 :       return ReducePhi(node);
      63             :     case IrOpcode::kEffectPhi:
      64     7781146 :       return PropagateDeadControl(node);
      65             :     case IrOpcode::kDeoptimize:
      66             :     case IrOpcode::kReturn:
      67             :     case IrOpcode::kTerminate:
      68             :     case IrOpcode::kTailCall:
      69     4593507 :       return ReduceDeoptimizeOrReturnOrTerminateOrTailCall(node);
      70             :     case IrOpcode::kThrow:
      71      900599 :       return PropagateDeadControl(node);
      72             :     case IrOpcode::kBranch:
      73             :     case IrOpcode::kSwitch:
      74     9915239 :       return ReduceBranchOrSwitch(node);
      75             :     default:
      76   274723434 :       return ReduceNode(node);
      77             :   }
      78             :   UNREACHABLE();
      79             : }
      80             : 
      81   159510088 : Reduction DeadCodeElimination::PropagateDeadControl(Node* node) {
      82             :   DCHECK_EQ(1, node->op()->ControlInputCount());
      83   159510088 :   Node* control = NodeProperties::GetControlInput(node);
      84   159499338 :   if (control->opcode() == IrOpcode::kDead) return Replace(control);
      85             :   return NoChange();
      86             : }
      87             : 
      88     3110201 : Reduction DeadCodeElimination::ReduceEnd(Node* node) {
      89             :   DCHECK_EQ(IrOpcode::kEnd, node->opcode());
      90             :   Node::Inputs inputs = node->inputs();
      91             :   DCHECK_LE(1, inputs.count());
      92             :   int live_input_count = 0;
      93    14372892 :   for (int i = 0; i < inputs.count(); ++i) {
      94    11354852 :     Node* const input = inputs[i];
      95             :     // Skip dead inputs.
      96    11354852 :     if (input->opcode() == IrOpcode::kDead) continue;
      97             :     // Compact live inputs.
      98    11188888 :     if (i != live_input_count) node->ReplaceInput(live_input_count, input);
      99    11188894 :     ++live_input_count;
     100             :   }
     101     3018040 :   if (live_input_count == 0) {
     102             :     return Replace(dead());
     103     3018025 :   } else if (live_input_count < inputs.count()) {
     104       92152 :     node->TrimInputCount(live_input_count);
     105      184304 :     NodeProperties::ChangeOp(node, common()->End(live_input_count));
     106             :     return Changed(node);
     107             :   }
     108             :   DCHECK_EQ(inputs.count(), live_input_count);
     109             :   return NoChange();
     110             : }
     111             : 
     112             : 
     113    15623832 : Reduction DeadCodeElimination::ReduceLoopOrMerge(Node* node) {
     114             :   DCHECK(IrOpcode::IsMergeOpcode(node->opcode()));
     115             :   Node::Inputs inputs = node->inputs();
     116             :   DCHECK_LE(1, inputs.count());
     117             :   // Count the number of live inputs to {node} and compact them on the fly, also
     118             :   // compacting the inputs of the associated {Phi} and {EffectPhi} uses at the
     119             :   // same time.  We consider {Loop}s dead even if only the first control input
     120             :   // is dead.
     121             :   int live_input_count = 0;
     122     8467881 :   if (node->opcode() != IrOpcode::kLoop ||
     123      667290 :       node->InputAt(0)->opcode() != IrOpcode::kDead) {
     124    27164671 :     for (int i = 0; i < inputs.count(); ++i) {
     125    27164614 :       Node* const input = inputs[i];
     126             :       // Skip dead inputs.
     127    27164614 :       if (input->opcode() == IrOpcode::kDead) continue;
     128             :       // Compact live inputs.
     129    26773185 :       if (live_input_count != i) {
     130      413954 :         node->ReplaceInput(live_input_count, input);
     131     2203129 :         for (Node* const use : node->uses()) {
     132     1375107 :           if (NodeProperties::IsPhi(use)) {
     133             :             DCHECK_EQ(inputs.count() + 1, use->InputCount());
     134      692039 :             use->ReplaceInput(live_input_count, use->InputAt(i));
     135             :           }
     136             :         }
     137             :       }
     138    26773242 :       ++live_input_count;
     139             :     }
     140             :   }
     141     7800648 :   if (live_input_count == 0) {
     142             :     return Replace(dead());
     143     7787533 :   } else if (live_input_count == 1) {
     144      521306 :     NodeVector loop_exits(zone_);
     145             :     // Due to compaction above, the live input is at offset 0.
     146     6845447 :     for (Node* const use : node->uses()) {
     147     2901417 :       if (NodeProperties::IsPhi(use)) {
     148      499851 :         Replace(use, use->InputAt(0));
     149     2560392 :       } else if (use->opcode() == IrOpcode::kLoopExit &&
     150             :                  use->InputAt(1) == node) {
     151             :         // Remember the loop exits so that we can mark their loop input dead.
     152             :         // This has to be done after the use list iteration so that we do
     153             :         // not mutate the use list while it is being iterated.
     154        2629 :         loop_exits.push_back(use);
     155     2553657 :       } else if (use->opcode() == IrOpcode::kTerminate) {
     156             :         DCHECK_EQ(IrOpcode::kLoop, node->opcode());
     157             :         Replace(use, dead());
     158             :       }
     159             :     }
     160     1045243 :     for (Node* loop_exit : loop_exits) {
     161        2629 :       loop_exit->ReplaceInput(1, dead());
     162             :       Revisit(loop_exit);
     163             :     }
     164             :     return Replace(node->InputAt(0));
     165             :   }
     166             :   DCHECK_LE(2, live_input_count);
     167             :   DCHECK_LE(live_input_count, inputs.count());
     168             :   // Trim input count for the {Merge} or {Loop} node.
     169     7266227 :   if (live_input_count < inputs.count()) {
     170             :     // Trim input counts for all phi uses and revisit them.
     171      530315 :     for (Node* const use : node->uses()) {
     172      320567 :       if (NodeProperties::IsPhi(use)) {
     173      145185 :         use->ReplaceInput(live_input_count, node);
     174      145185 :         TrimMergeOrPhi(use, live_input_count);
     175             :         Revisit(use);
     176             :       }
     177             :     }
     178      104874 :     TrimMergeOrPhi(node, live_input_count);
     179             :     return Changed(node);
     180             :   }
     181             :   return NoChange();
     182             : }
     183             : 
     184       18742 : Reduction DeadCodeElimination::RemoveLoopExit(Node* node) {
     185             :   DCHECK_EQ(IrOpcode::kLoopExit, node->opcode());
     186      179054 :   for (Node* const use : node->uses()) {
     187       70785 :     if (use->opcode() == IrOpcode::kLoopExitValue ||
     188             :         use->opcode() == IrOpcode::kLoopExitEffect) {
     189       70643 :       Replace(use, use->InputAt(0));
     190             :     }
     191             :   }
     192       18742 :   Node* control = NodeProperties::GetControlInput(node, 0);
     193             :   Replace(node, control);
     194       18742 :   return Replace(control);
     195             : }
     196             : 
     197   296675124 : Reduction DeadCodeElimination::ReduceNode(Node* node) {
     198             :   DCHECK(!IrOpcode::IsGraphTerminator(node->opcode()));
     199   274774972 :   int const effect_input_count = node->op()->EffectInputCount();
     200   274774972 :   int const control_input_count = node->op()->ControlInputCount();
     201             :   DCHECK_LE(control_input_count, 1);
     202   274774972 :   if (control_input_count == 1) {
     203   130005944 :     Reduction reduction = PropagateDeadControl(node);
     204   130000259 :     if (reduction.Changed()) return reduction;
     205             :   }
     206   549029048 :   if (effect_input_count == 0 &&
     207    21900152 :       (control_input_count == 0 || node->op()->ControlOutputCount() == 0)) {
     208   140907374 :     return ReducePureNode(node);
     209             :   }
     210   133607150 :   if (effect_input_count > 0) {
     211   113127426 :     return ReduceEffectNode(node);
     212             :   }
     213             :   return NoChange();
     214             : }
     215             : 
     216    12289169 : Reduction DeadCodeElimination::ReducePhi(Node* node) {
     217             :   DCHECK_EQ(IrOpcode::kPhi, node->opcode());
     218     4149174 :   Reduction reduction = PropagateDeadControl(node);
     219     4148901 :   if (reduction.Changed()) return reduction;
     220     4070537 :   MachineRepresentation rep = PhiRepresentationOf(node->op());
     221    12208700 :   if (rep == MachineRepresentation::kNone ||
     222    12210118 :       NodeProperties::GetTypeOrAny(node).IsNone()) {
     223          56 :     return Replace(DeadValue(node, rep));
     224             :   }
     225     4069458 :   int input_count = node->op()->ValueInputCount();
     226    20467206 :   for (int i = 0; i < input_count; ++i) {
     227    16397745 :     Node* input = NodeProperties::GetValueInput(node, i);
     228    16399826 :     if (input->opcode() == IrOpcode::kDeadValue &&
     229        2132 :         DeadValueRepresentationOf(input->op()) != rep) {
     230         687 :       NodeProperties::ReplaceValueInput(node, DeadValue(input, rep), i);
     231             :     }
     232             :   }
     233             :   return NoChange();
     234             : }
     235             : 
     236   140907678 : Reduction DeadCodeElimination::ReducePureNode(Node* node) {
     237             :   DCHECK_EQ(0, node->op()->EffectInputCount());
     238   140907678 :   if (node->opcode() == IrOpcode::kDeadValue) return NoChange();
     239   140847463 :   if (Node* input = FindDeadInput(node)) {
     240      104517 :     return Replace(DeadValue(input));
     241             :   }
     242             :   return NoChange();
     243             : }
     244             : 
     245     2195315 : Reduction DeadCodeElimination::ReduceUnreachableOrIfException(Node* node) {
     246             :   DCHECK(node->opcode() == IrOpcode::kUnreachable ||
     247             :          node->opcode() == IrOpcode::kIfException);
     248     2195315 :   Reduction reduction = PropagateDeadControl(node);
     249     2195309 :   if (reduction.Changed()) return reduction;
     250     2145867 :   Node* effect = NodeProperties::GetEffectInput(node, 0);
     251     2145860 :   if (effect->opcode() == IrOpcode::kDead) {
     252             :     return Replace(effect);
     253             :   }
     254     2145783 :   if (effect->opcode() == IrOpcode::kUnreachable) {
     255             :     return Replace(effect);
     256             :   }
     257             :   return NoChange();
     258             : }
     259             : 
     260   113130942 : Reduction DeadCodeElimination::ReduceEffectNode(Node* node) {
     261             :   DCHECK_EQ(1, node->op()->EffectInputCount());
     262   113134033 :   Node* effect = NodeProperties::GetEffectInput(node, 0);
     263   113124186 :   if (effect->opcode() == IrOpcode::kDead) {
     264             :     return Replace(effect);
     265             :   }
     266   113115531 :   if (Node* input = FindDeadInput(node)) {
     267        7638 :     if (effect->opcode() == IrOpcode::kUnreachable) {
     268        1497 :       RelaxEffectsAndControls(node);
     269        6141 :       return Replace(DeadValue(input));
     270             :     }
     271             : 
     272        1497 :     Node* control = node->op()->ControlInputCount() == 1
     273             :                         ? NodeProperties::GetControlInput(node, 0)
     274        1553 :                         : graph()->start();
     275             :     Node* unreachable =
     276        1497 :         graph()->NewNode(common()->Unreachable(), effect, control);
     277             :     NodeProperties::SetType(unreachable, Type::None());
     278        1497 :     ReplaceWithValue(node, DeadValue(input), node, control);
     279             :     return Replace(unreachable);
     280             :   }
     281             : 
     282             :   return NoChange();
     283             : }
     284             : 
     285     4593509 : Reduction DeadCodeElimination::ReduceDeoptimizeOrReturnOrTerminateOrTailCall(
     286         285 :     Node* node) {
     287             :   DCHECK(node->opcode() == IrOpcode::kDeoptimize ||
     288             :          node->opcode() == IrOpcode::kReturn ||
     289             :          node->opcode() == IrOpcode::kTerminate ||
     290             :          node->opcode() == IrOpcode::kTailCall);
     291     4593509 :   Reduction reduction = PropagateDeadControl(node);
     292     4593519 :   if (reduction.Changed()) return reduction;
     293     4560647 :   if (FindDeadInput(node) != nullptr) {
     294         426 :     Node* effect = NodeProperties::GetEffectInput(node, 0);
     295         213 :     Node* control = NodeProperties::GetControlInput(node, 0);
     296         213 :     if (effect->opcode() != IrOpcode::kUnreachable) {
     297          36 :       effect = graph()->NewNode(common()->Unreachable(), effect, control);
     298             :       NodeProperties::SetType(effect, Type::None());
     299             :     }
     300         213 :     node->TrimInputCount(2);
     301         213 :     node->ReplaceInput(0, effect);
     302         213 :     node->ReplaceInput(1, control);
     303         213 :     NodeProperties::ChangeOp(node, common()->Throw());
     304             :     return Changed(node);
     305             :   }
     306             :   return NoChange();
     307             : }
     308             : 
     309      344176 : Reduction DeadCodeElimination::ReduceLoopExit(Node* node) {
     310      688352 :   Node* control = NodeProperties::GetControlInput(node, 0);
     311      671894 :   Node* loop = NodeProperties::GetControlInput(node, 1);
     312      671894 :   if (control->opcode() == IrOpcode::kDead ||
     313             :       loop->opcode() == IrOpcode::kDead) {
     314       18742 :     return RemoveLoopExit(node);
     315             :   }
     316             :   return NoChange();
     317             : }
     318             : 
     319     9916637 : Reduction DeadCodeElimination::ReduceBranchOrSwitch(Node* node) {
     320             :   DCHECK(node->opcode() == IrOpcode::kBranch ||
     321             :          node->opcode() == IrOpcode::kSwitch);
     322     9915231 :   Reduction reduction = PropagateDeadControl(node);
     323     9915237 :   if (reduction.Changed()) return reduction;
     324     9889161 :   Node* condition = NodeProperties::GetValueInput(node, 0);
     325     9889141 :   if (condition->opcode() == IrOpcode::kDeadValue) {
     326             :     // Branches or switches on {DeadValue} must originate from unreachable code
     327             :     // and cannot matter. Due to schedule freedom between the effect and the
     328             :     // control chain, they might still appear in reachable code. Remove them by
     329             :     // always choosing the first projection.
     330        1406 :     size_t const projection_cnt = node->op()->ControlOutputCount();
     331         703 :     Node** projections = zone_->NewArray<Node*>(projection_cnt);
     332             :     NodeProperties::CollectControlProjections(node, projections,
     333         703 :                                               projection_cnt);
     334         703 :     Replace(projections[0], NodeProperties::GetControlInput(node));
     335             :     return Replace(dead());
     336             :   }
     337             :   return NoChange();
     338             : }
     339             : 
     340      250059 : void DeadCodeElimination::TrimMergeOrPhi(Node* node, int size) {
     341      250059 :   const Operator* const op = common()->ResizeMergeOrPhi(node->op(), size);
     342      250059 :   node->TrimInputCount(OperatorProperties::GetTotalInputCount(op));
     343      250059 :   NodeProperties::ChangeOp(node, op);
     344      250059 : }
     345             : 
     346      228252 : Node* DeadCodeElimination::DeadValue(Node* node, MachineRepresentation rep) {
     347      112898 :   if (node->opcode() == IrOpcode::kDeadValue) {
     348       56013 :     if (rep == DeadValueRepresentationOf(node->op())) return node;
     349         792 :     node = NodeProperties::GetValueInput(node, 0);
     350             :   }
     351       57677 :   Node* dead_value = graph()->NewNode(common()->DeadValue(rep), node);
     352             :   NodeProperties::SetType(dead_value, Type::None());
     353       57677 :   return dead_value;
     354             : }
     355             : 
     356             : }  // namespace compiler
     357             : }  // namespace internal
     358      178779 : }  // namespace v8

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