92 lines
3.1 KiB
C++
92 lines
3.1 KiB
C++
// Copyright (c) 2017 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef SOURCE_OPT_VALUE_NUMBER_TABLE_H_
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#define SOURCE_OPT_VALUE_NUMBER_TABLE_H_
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#include <cstdint>
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#include <unordered_map>
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#include "source/opt/instruction.h"
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namespace spvtools {
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namespace opt {
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class IRContext;
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// Returns true if the two instructions compute the same value. Used by the
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// value number table to compare two instructions.
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class ComputeSameValue {
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public:
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bool operator()(const Instruction& lhs, const Instruction& rhs) const;
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};
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// The hash function used in the value number table.
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class ValueTableHash {
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public:
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std::size_t operator()(const Instruction& inst) const;
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};
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// This class implements the value number analysis. It is using a hash-based
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// approach to value numbering. It is essentially doing dominator-tree value
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// numbering described in
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//
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// Preston Briggs, Keith D. Cooper, and L. Taylor Simpson. 1997. Value
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// numbering. Softw. Pract. Exper. 27, 6 (June 1997), 701-724.
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// https://www.cs.rice.edu/~keith/Promo/CRPC-TR94517.pdf.gz
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//
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// The main difference is that because we do not perform redundancy elimination
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// as we build the value number table, we do not have to deal with cleaning up
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// the scope.
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class ValueNumberTable {
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public:
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ValueNumberTable(IRContext* ctx) : context_(ctx), next_value_number_(1) {
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BuildDominatorTreeValueNumberTable();
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}
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// Returns the value number of the value computed by |inst|. |inst| must have
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// a result id that will hold the computed value. If no value number has been
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// assigned to the result id, then the return value is 0.
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uint32_t GetValueNumber(Instruction* inst) const;
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// Returns the value number of the value contain in |id|. Returns 0 if it
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// has not been assigned a value number.
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uint32_t GetValueNumber(uint32_t id) const;
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IRContext* context() const { return context_; }
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private:
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// Assigns a value number to every result id in the module.
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void BuildDominatorTreeValueNumberTable();
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// Returns the new value number.
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uint32_t TakeNextValueNumber() { return next_value_number_++; }
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// Assigns a new value number to the result of |inst| if it does not already
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// have one. Return the value number for |inst|. |inst| must have a result
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// id.
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uint32_t AssignValueNumber(Instruction* inst);
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std::unordered_map<Instruction, uint32_t, ValueTableHash, ComputeSameValue>
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instruction_to_value_;
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std::unordered_map<uint32_t, uint32_t> id_to_value_;
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IRContext* context_;
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uint32_t next_value_number_;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_VALUE_NUMBER_TABLE_H_
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