f9a88acbc9
TBR=mvstanton@chromium.org,neis@chromium.org,ahaas@chromium.org Bug: v8:9247 Change-Id: I5433c863a54f3412d73df0d38aba3fdbcfac7ebe Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1627973 Commit-Queue: Yang Guo <yangguo@chromium.org> Auto-Submit: Yang Guo <yangguo@chromium.org> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org> Cr-Commit-Position: refs/heads/master@{#61830}
88 lines
3.3 KiB
C++
88 lines
3.3 KiB
C++
// Copyright 2015 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_COMPILER_DEAD_CODE_ELIMINATION_H_
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#define V8_COMPILER_DEAD_CODE_ELIMINATION_H_
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#include "src/base/compiler-specific.h"
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#include "src/codegen/machine-type.h"
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#include "src/common/globals.h"
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#include "src/compiler/graph-reducer.h"
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namespace v8 {
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namespace internal {
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namespace compiler {
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// Forward declarations.
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class CommonOperatorBuilder;
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// Propagates {Dead} control and {DeadValue} values through the graph and
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// thereby removes dead code.
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// We detect dead values based on types, replacing uses of nodes with
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// {Type::None()} with {DeadValue}. A pure node (other than a phi) using
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// {DeadValue} is replaced by {DeadValue}. When {DeadValue} hits the effect
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// chain, a crashing {Unreachable} node is inserted and the rest of the effect
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// chain is collapsed. We wait for the {EffectControlLinearizer} to connect
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// {Unreachable} nodes to the graph end, since this is much easier if there is
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// no floating control.
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// {DeadValue} has an input, which has to have {Type::None()}. This input is
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// important to maintain the dependency on the cause of the unreachable code.
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// {Unreachable} has a value output and {Type::None()} so it can be used by
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// {DeadValue}.
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// {DeadValue} nodes track a {MachineRepresentation} so they can be lowered to a
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// value-producing node. {DeadValue} has the runtime semantics of crashing and
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// behaves like a constant of its representation so it can be used in gap moves.
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// Since phi nodes are the only remaining use of {DeadValue}, this
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// representation is only adjusted for uses by phi nodes.
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// In contrast to {DeadValue}, {Dead} can never remain in the graph.
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class V8_EXPORT_PRIVATE DeadCodeElimination final
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: public NON_EXPORTED_BASE(AdvancedReducer) {
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public:
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DeadCodeElimination(Editor* editor, Graph* graph,
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CommonOperatorBuilder* common, Zone* temp_zone);
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~DeadCodeElimination() final = default;
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const char* reducer_name() const override { return "DeadCodeElimination"; }
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Reduction Reduce(Node* node) final;
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private:
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Reduction ReduceEnd(Node* node);
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Reduction ReduceLoopOrMerge(Node* node);
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Reduction ReduceLoopExit(Node* node);
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Reduction ReduceNode(Node* node);
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Reduction ReducePhi(Node* node);
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Reduction ReduceEffectPhi(Node* node);
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Reduction ReducePureNode(Node* node);
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Reduction ReduceUnreachableOrIfException(Node* node);
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Reduction ReduceEffectNode(Node* node);
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Reduction ReduceDeoptimizeOrReturnOrTerminateOrTailCall(Node* node);
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Reduction ReduceBranchOrSwitch(Node* node);
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Reduction RemoveLoopExit(Node* node);
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Reduction PropagateDeadControl(Node* node);
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void TrimMergeOrPhi(Node* node, int size);
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Node* DeadValue(Node* none_node,
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MachineRepresentation rep = MachineRepresentation::kNone);
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Graph* graph() const { return graph_; }
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CommonOperatorBuilder* common() const { return common_; }
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Node* dead() const { return dead_; }
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Graph* const graph_;
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CommonOperatorBuilder* const common_;
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Node* const dead_;
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Zone* zone_;
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DISALLOW_COPY_AND_ASSIGN(DeadCodeElimination);
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};
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} // namespace compiler
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} // namespace internal
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} // namespace v8
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#endif // V8_COMPILER_DEAD_CODE_ELIMINATION_H_
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