e1cdda2512
In addition to using the {Dead} node to prune dead control nodes and nodes that
depend on them, we introduce a {DeadValue} node representing an impossible value
that can occur at any position in the graph. The extended {DeadCodeElimination}
prunes {DeadValue} and its uses, inserting a crashing {Unreachable} node into
the effect chain when possible. The remaining uses of {DeadValue} are handled
in {EffectControlLinearizer}, where we always have access to the effect chain.
In addition to explicitly introduced {DeadValue} nodes, we consider any value use
of a node with type {None} as dead.
Bug: chromium:741225
Change-Id: Icc4b636d1d018c452ba1a2fa7cd3e00e522f1655
Reviewed-on: https://chromium-review.googlesource.com/641250
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48208}
68 lines
2.2 KiB
C++
68 lines
2.2 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/compiler/graph-reducer.h"
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#include "src/globals.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. When {DeadValue} hits the effect chain, a crashing
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// {Unreachable} node is inserted and the rest of the effect chain is collapsed.
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// We detect dead values based on types, pruning uses of DeadValue except for
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// uses by phi and control nodes without effect input. These remaining uses of
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// {DeadValue} are eliminated in the {EffectControlLinearizer}, when the effect
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// chain is readily available to insert an {Unreachable} node for safety. In
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// contrast to this, {Dead} must not 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);
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~DeadCodeElimination() final {}
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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 ReducePureNode(Node* node);
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Reduction ReduceEffectNode(Node* node);
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Reduction RemoveLoopExit(Node* node);
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void TrimMergeOrPhi(Node* node, int size);
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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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Node* dead_value() const { return dead_value_; }
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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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Node* const dead_value_;
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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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