LCOV - code coverage report
Current view: top level - src/compiler - dead-code-elimination.cc (source / functions) Hit Total Coverage
Test: app.info Lines: 136 137 99.3 %
Date: 2019-04-17 Functions: 18 19 94.7 %

          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     2860206 : DeadCodeElimination::DeadCodeElimination(Editor* editor, Graph* graph,
      18             :                                          CommonOperatorBuilder* common,
      19             :                                          Zone* temp_zone)
      20             :     : AdvancedReducer(editor),
      21             :       graph_(graph),
      22             :       common_(common),
      23     2860206 :       dead_(graph->NewNode(common->Dead())),
      24     5720420 :       zone_(temp_zone) {
      25             :   NodeProperties::SetType(dead_, Type::None());
      26     2860214 : }
      27             : 
      28             : namespace {
      29             : 
      30             : // True if we can guarantee that {node} will never actually produce a value or
      31             : // effect.
      32   771684012 : bool NoReturn(Node* node) {
      33   771633234 :   return node->opcode() == IrOpcode::kDead ||
      34   771631934 :          node->opcode() == IrOpcode::kUnreachable ||
      35  1543260991 :          node->opcode() == IrOpcode::kDeadValue ||
      36  1543260991 :          NodeProperties::GetTypeOrAny(node).IsNone();
      37             : }
      38             : 
      39   247395258 : Node* FindDeadInput(Node* node) {
      40  1018972023 :   for (Node* input : node->inputs()) {
      41   771683019 :     if (NoReturn(input)) return input;
      42             :   }
      43             :   return nullptr;
      44             : }
      45             : 
      46             : }  // namespace
      47             : 
      48   302825066 : Reduction DeadCodeElimination::Reduce(Node* node) {
      49             :   DisallowHeapAccess no_heap_access;
      50   302825066 :   switch (node->opcode()) {
      51             :     case IrOpcode::kEnd:
      52     3050688 :       return ReduceEnd(node);
      53             :     case IrOpcode::kLoop:
      54             :     case IrOpcode::kMerge:
      55     7497451 :       return ReduceLoopOrMerge(node);
      56             :     case IrOpcode::kLoopExit:
      57      352078 :       return ReduceLoopExit(node);
      58             :     case IrOpcode::kUnreachable:
      59             :     case IrOpcode::kIfException:
      60     2273687 :       return ReduceUnreachableOrIfException(node);
      61             :     case IrOpcode::kPhi:
      62     3952022 :       return ReducePhi(node);
      63             :     case IrOpcode::kEffectPhi:
      64             :       return PropagateDeadControl(node);
      65             :     case IrOpcode::kDeoptimize:
      66             :     case IrOpcode::kReturn:
      67             :     case IrOpcode::kTerminate:
      68             :     case IrOpcode::kTailCall:
      69     4581237 :       return ReduceDeoptimizeOrReturnOrTerminateOrTailCall(node);
      70             :     case IrOpcode::kThrow:
      71             :       return PropagateDeadControl(node);
      72             :     case IrOpcode::kBranch:
      73             :     case IrOpcode::kSwitch:
      74     9605622 :       return ReduceBranchOrSwitch(node);
      75             :     default:
      76   263056912 :       return ReduceNode(node);
      77             :   }
      78             :   UNREACHABLE();
      79             : }
      80             : 
      81           0 : Reduction DeadCodeElimination::PropagateDeadControl(Node* node) {
      82             :   DCHECK_EQ(1, node->op()->ControlInputCount());
      83   153443690 :   Node* control = NodeProperties::GetControlInput(node);
      84   153428503 :   if (control->opcode() == IrOpcode::kDead) return Replace(control);
      85             :   return NoChange();
      86             : }
      87             : 
      88     3050688 : 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    23187794 :   for (int i = 0; i < inputs.count(); ++i) {
      94             :     Node* const input = inputs[i];
      95             :     // Skip dead inputs.
      96    10068552 :     if (input->opcode() == IrOpcode::kDead) continue;
      97             :     // Compact live inputs.
      98     9900692 :     if (i != live_input_count) node->ReplaceInput(live_input_count, input);
      99     9900693 :     ++live_input_count;
     100             :   }
     101     3050689 :   if (live_input_count == 0) {
     102             :     return Replace(dead());
     103     3050674 :   } else if (live_input_count < inputs.count()) {
     104       94314 :     node->TrimInputCount(live_input_count);
     105       94313 :     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     7497483 : 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     8137274 :   if (node->opcode() != IrOpcode::kLoop ||
     123             :       node->InputAt(0)->opcode() != IrOpcode::kDead) {
     124    60150642 :     for (int i = 0; i < inputs.count(); ++i) {
     125             :       Node* const input = inputs[i];
     126             :       // Skip dead inputs.
     127    26327354 :       if (input->opcode() == IrOpcode::kDead) continue;
     128             :       // Compact live inputs.
     129    25935826 :       if (live_input_count != i) {
     130      415686 :         node->ReplaceInput(live_input_count, input);
     131     1788478 :         for (Node* const use : node->uses()) {
     132     1372792 :           if (NodeProperties::IsPhi(use)) {
     133             :             DCHECK_EQ(inputs.count() + 1, use->InputCount());
     134      686055 :             use->ReplaceInput(live_input_count, use->InputAt(i));
     135             :           }
     136             :         }
     137             :       }
     138    25935826 :       ++live_input_count;
     139             :     }
     140             :   }
     141     7497483 :   if (live_input_count == 0) {
     142             :     return Replace(dead());
     143     7484117 :   } else if (live_input_count == 1) {
     144      517230 :     NodeVector loop_exits(zone_);
     145             :     // Due to compaction above, the live input is at offset 0.
     146     6297485 :     for (Node* const use : node->uses()) {
     147     2890128 :       if (NodeProperties::IsPhi(use)) {
     148             :         Replace(use, use->InputAt(0));
     149     2546456 :       } 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        2218 :         loop_exits.push_back(use);
     155     2540617 :       } else if (use->opcode() == IrOpcode::kTerminate) {
     156             :         DCHECK_EQ(IrOpcode::kLoop, node->opcode());
     157             :         Replace(use, dead());
     158             :       }
     159             :     }
     160      519447 :     for (Node* loop_exit : loop_exits) {
     161        2218 :       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     6966887 :   if (live_input_count < inputs.count()) {
     170             :     // Trim input counts for all phi uses and revisit them.
     171      422427 :     for (Node* const use : node->uses()) {
     172      317819 :       if (NodeProperties::IsPhi(use)) {
     173      142969 :         use->ReplaceInput(live_input_count, node);
     174      142969 :         TrimMergeOrPhi(use, live_input_count);
     175             :         Revisit(use);
     176             :       }
     177             :     }
     178      104608 :     TrimMergeOrPhi(node, live_input_count);
     179             :     return Changed(node);
     180             :   }
     181             :   return NoChange();
     182             : }
     183             : 
     184       14570 : Reduction DeadCodeElimination::RemoveLoopExit(Node* node) {
     185             :   DCHECK_EQ(IrOpcode::kLoopExit, node->opcode());
     186       69816 :   for (Node* const use : node->uses()) {
     187       55246 :     if (use->opcode() == IrOpcode::kLoopExitValue ||
     188             :         use->opcode() == IrOpcode::kLoopExitEffect) {
     189             :       Replace(use, use->InputAt(0));
     190             :     }
     191             :   }
     192       14570 :   Node* control = NodeProperties::GetControlInput(node, 0);
     193             :   Replace(node, control);
     194       14570 :   return Replace(control);
     195             : }
     196             : 
     197   263121474 : Reduction DeadCodeElimination::ReduceNode(Node* node) {
     198             :   DCHECK(!IrOpcode::IsGraphTerminator(node->opcode()));
     199             :   int const effect_input_count = node->op()->EffectInputCount();
     200             :   int const control_input_count = node->op()->ControlInputCount();
     201             :   DCHECK_LE(control_input_count, 1);
     202   263121474 :   if (control_input_count == 1) {
     203             :     Reduction reduction = PropagateDeadControl(node);
     204   124561697 :     if (reduction.Changed()) return reduction;
     205             :   }
     206   525701958 :   if (effect_input_count == 0 &&
     207    21329702 :       (control_input_count == 0 || node->op()->ControlOutputCount() == 0)) {
     208   134638121 :     return ReducePureNode(node);
     209             :   }
     210   128212858 :   if (effect_input_count > 0) {
     211   108329606 :     return ReduceEffectNode(node);
     212             :   }
     213             :   return NoChange();
     214             : }
     215             : 
     216     3951863 : Reduction DeadCodeElimination::ReducePhi(Node* node) {
     217             :   DCHECK_EQ(IrOpcode::kPhi, node->opcode());
     218             :   Reduction reduction = PropagateDeadControl(node);
     219     3951207 :   if (reduction.Changed()) return reduction;
     220     3870875 :   MachineRepresentation rep = PhiRepresentationOf(node->op());
     221     7739965 :   if (rep == MachineRepresentation::kNone ||
     222     3870688 :       NodeProperties::GetTypeOrAny(node).IsNone()) {
     223          64 :     return Replace(DeadValue(node, rep));
     224             :   }
     225             :   int input_count = node->op()->ValueInputCount();
     226    36973745 :   for (int i = 0; i < input_count; ++i) {
     227    16552481 :     Node* input = NodeProperties::GetValueInput(node, i);
     228    16554754 :     if (input->opcode() == IrOpcode::kDeadValue &&
     229        2461 :         DeadValueRepresentationOf(input->op()) != rep) {
     230         809 :       NodeProperties::ReplaceValueInput(node, DeadValue(input, rep), i);
     231             :     }
     232             :   }
     233             :   return NoChange();
     234             : }
     235             : 
     236   134637975 : Reduction DeadCodeElimination::ReducePureNode(Node* node) {
     237             :   DCHECK_EQ(0, node->op()->EffectInputCount());
     238   134637975 :   if (node->opcode() == IrOpcode::kDeadValue) return NoChange();
     239   134576082 :   if (Node* input = FindDeadInput(node)) {
     240      105699 :     return Replace(DeadValue(input));
     241             :   }
     242             :   return NoChange();
     243             : }
     244             : 
     245     2273682 : Reduction DeadCodeElimination::ReduceUnreachableOrIfException(Node* node) {
     246             :   DCHECK(node->opcode() == IrOpcode::kUnreachable ||
     247             :          node->opcode() == IrOpcode::kIfException);
     248             :   Reduction reduction = PropagateDeadControl(node);
     249     2273676 :   if (reduction.Changed()) return reduction;
     250     2229735 :   Node* effect = NodeProperties::GetEffectInput(node, 0);
     251     2229712 :   if (effect->opcode() == IrOpcode::kDead) {
     252             :     return Replace(effect);
     253             :   }
     254     2229603 :   if (effect->opcode() == IrOpcode::kUnreachable) {
     255             :     return Replace(effect);
     256             :   }
     257             :   return NoChange();
     258             : }
     259             : 
     260   108328726 : Reduction DeadCodeElimination::ReduceEffectNode(Node* node) {
     261             :   DCHECK_EQ(1, node->op()->EffectInputCount());
     262   108328726 :   Node* effect = NodeProperties::GetEffectInput(node, 0);
     263   108324453 :   if (effect->opcode() == IrOpcode::kDead) {
     264             :     return Replace(effect);
     265             :   }
     266   108315707 :   if (Node* input = FindDeadInput(node)) {
     267        8861 :     if (effect->opcode() == IrOpcode::kUnreachable) {
     268             :       RelaxEffectsAndControls(node);
     269        7243 :       return Replace(DeadValue(input));
     270             :     }
     271             : 
     272             :     Node* control = node->op()->ControlInputCount() == 1
     273             :                         ? NodeProperties::GetControlInput(node, 0)
     274        1618 :                         : graph()->start();
     275             :     Node* unreachable =
     276        1618 :         graph()->NewNode(common()->Unreachable(), effect, control);
     277             :     NodeProperties::SetType(unreachable, Type::None());
     278             :     ReplaceWithValue(node, DeadValue(input), node, control);
     279             :     return Replace(unreachable);
     280             :   }
     281             : 
     282             :   return NoChange();
     283             : }
     284             : 
     285     4581237 : Reduction DeadCodeElimination::ReduceDeoptimizeOrReturnOrTerminateOrTailCall(
     286             :     Node* node) {
     287             :   DCHECK(node->opcode() == IrOpcode::kDeoptimize ||
     288             :          node->opcode() == IrOpcode::kReturn ||
     289             :          node->opcode() == IrOpcode::kTerminate ||
     290             :          node->opcode() == IrOpcode::kTailCall);
     291             :   Reduction reduction = PropagateDeadControl(node);
     292     4581243 :   if (reduction.Changed()) return reduction;
     293     4548694 :   if (FindDeadInput(node) != nullptr) {
     294         302 :     Node* effect = NodeProperties::GetEffectInput(node, 0);
     295         302 :     Node* control = NodeProperties::GetControlInput(node, 0);
     296         302 :     if (effect->opcode() != IrOpcode::kUnreachable) {
     297          83 :       effect = graph()->NewNode(common()->Unreachable(), effect, control);
     298             :       NodeProperties::SetType(effect, Type::None());
     299             :     }
     300         302 :     node->TrimInputCount(2);
     301         302 :     node->ReplaceInput(0, effect);
     302         302 :     node->ReplaceInput(1, control);
     303         302 :     NodeProperties::ChangeOp(node, common()->Throw());
     304             :     return Changed(node);
     305             :   }
     306             :   return NoChange();
     307             : }
     308             : 
     309      352077 : Reduction DeadCodeElimination::ReduceLoopExit(Node* node) {
     310      352077 :   Node* control = NodeProperties::GetControlInput(node, 0);
     311      352076 :   Node* loop = NodeProperties::GetControlInput(node, 1);
     312      691643 :   if (control->opcode() == IrOpcode::kDead ||
     313             :       loop->opcode() == IrOpcode::kDead) {
     314       14570 :     return RemoveLoopExit(node);
     315             :   }
     316             :   return NoChange();
     317             : }
     318             : 
     319     9605591 : Reduction DeadCodeElimination::ReduceBranchOrSwitch(Node* node) {
     320             :   DCHECK(node->opcode() == IrOpcode::kBranch ||
     321             :          node->opcode() == IrOpcode::kSwitch);
     322             :   Reduction reduction = PropagateDeadControl(node);
     323     9605441 :   if (reduction.Changed()) return reduction;
     324     9579428 :   Node* condition = NodeProperties::GetValueInput(node, 0);
     325     9579397 :   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         702 :     size_t const projection_cnt = node->op()->ControlOutputCount();
     331         702 :     Node** projections = zone_->NewArray<Node*>(projection_cnt);
     332             :     NodeProperties::CollectControlProjections(node, projections,
     333         702 :                                               projection_cnt);
     334         702 :     Replace(projections[0], NodeProperties::GetControlInput(node));
     335             :     return Replace(dead());
     336             :   }
     337             :   return NoChange();
     338             : }
     339             : 
     340      247577 : void DeadCodeElimination::TrimMergeOrPhi(Node* node, int size) {
     341      247577 :   const Operator* const op = common()->ResizeMergeOrPhi(node->op(), size);
     342      247577 :   node->TrimInputCount(OperatorProperties::GetTotalInputCount(op));
     343      247577 :   NodeProperties::ChangeOp(node, op);
     344      247577 : }
     345             : 
     346      115433 : Node* DeadCodeElimination::DeadValue(Node* node, MachineRepresentation rep) {
     347      115433 :   if (node->opcode() == IrOpcode::kDeadValue) {
     348       57282 :     if (rep == DeadValueRepresentationOf(node->op())) return node;
     349         925 :     node = NodeProperties::GetValueInput(node, 0);
     350             :   }
     351       59076 :   Node* dead_value = graph()->NewNode(common()->DeadValue(rep), node);
     352             :   NodeProperties::SetType(dead_value, Type::None());
     353       59076 :   return dead_value;
     354             : }
     355             : 
     356             : }  // namespace compiler
     357             : }  // namespace internal
     358      121996 : }  // namespace v8

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