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https://github.com/KhronosGroup/SPIRV-Tools
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dd4157dcee
Add code sinking pass. It will move OpLoad and OpAccessChain instructions as close as possible to their uses. Part of #1611.
108 lines
4.3 KiB
C++
108 lines
4.3 KiB
C++
// Copyright (c) 2019 Google LLC
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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_CODE_SINK_H_
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#define SOURCE_OPT_CODE_SINK_H_
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#include <unordered_map>
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#include "source/opt/ir_context.h"
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#include "source/opt/module.h"
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#include "source/opt/pass.h"
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namespace spvtools {
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namespace opt {
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// This pass does code sinking for OpAccessChain and OpLoad on variables in
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// uniform storage or in read only memory. Code sinking is a transformation
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// where an instruction is moved into a more deeply nested construct.
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//
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// The goal is to move these instructions as close as possible to their uses
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// without having to execute them more often or to replicate the instruction.
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// Moving the instruction in this way can lead to shorter live ranges, which can
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// lead to less register pressure. It can also cause instructions to be
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// executed less often because they could be moved into one path of a selection
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// construct.
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//
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// This optimization can cause register pressure to rise if the operands of the
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// instructions go dead after the instructions being moved. That is why we only
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// move certain OpLoad and OpAccessChain instructions. They generally have
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// constants, loop induction variables, and global pointers as operands. The
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// operands are live for a longer time in most cases.
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class CodeSinkingPass : public Pass {
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public:
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const char* name() const override { return "code-sink"; }
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Status Process() override;
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// Return the mask of preserved Analyses.
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IRContext::Analysis GetPreservedAnalyses() override {
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return IRContext::kAnalysisDefUse |
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IRContext::kAnalysisInstrToBlockMapping |
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IRContext::kAnalysisCombinators | IRContext::kAnalysisCFG |
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IRContext::kAnalysisDominatorAnalysis |
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IRContext::kAnalysisLoopAnalysis | IRContext::kAnalysisNameMap |
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IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
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}
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private:
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// Sinks the instructions in |bb| as much as possible. Returns true if
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// something changes.
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bool SinkInstructionsInBB(BasicBlock* bb);
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// Tries the sink |inst| as much as possible. Returns true if the instruction
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// is moved.
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bool SinkInstruction(Instruction* inst);
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// Returns the basic block in which to move |inst| to move is as close as
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// possible to the uses of |inst| without increasing the number of times
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// |inst| will be executed. Return |nullptr| if there is no need to move
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// |inst|.
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BasicBlock* FindNewBasicBlockFor(Instruction* inst);
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// Return true if |inst| reference memory and it is possible that the data in
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// the memory changes at some point.
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bool ReferencesMutableMemory(Instruction* inst);
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// Returns true if the module contains an instruction that has a memory
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// semantics id as an operand, and the memory semantics enforces a
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// synchronization of uniform memory. See section 3.25 of the SPIR-V
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// specification.
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bool HasUniformMemorySync();
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// Returns true if there may be a store to the variable |var_inst|.
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bool HasPossibleStore(Instruction* var_inst);
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// Returns true if one of the basic blocks in |set| exists on a path from the
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// basic block |start| to |end|.
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bool IntersectsPath(uint32_t start, uint32_t end,
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const std::unordered_set<uint32_t>& set);
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// Returns true if |mem_semantics_id| is the id of a constant that, when
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// interpreted as a memory semantics mask enforces synchronization of uniform
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// memory. See section 3.25 of the SPIR-V specification.
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bool IsSyncOnUniform(uint32_t mem_semantics_id) const;
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// True if a check has for uniform storage has taken place.
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bool checked_for_uniform_sync_;
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// Cache of whether or not the module has a memory sync on uniform storage.
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// only valid if |check_for_uniform_sync_| is true.
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bool has_uniform_sync_;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_CODE_SINK_H_
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