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// Copyright (c) 2019 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <unordered_map>
#include "source/opt/ir_context.h"
#include "source/opt/module.h"
#include "source/opt/pass.h"
namespace spvtools {
namespace opt {
// This pass does code sinking for OpAccessChain and OpLoad on variables in
// uniform storage or in read only memory. Code sinking is a transformation
// where an instruction is moved into a more deeply nested construct.
// The goal is to move these instructions as close as possible to their uses
// without having to execute them more often or to replicate the instruction.
// Moving the instruction in this way can lead to shorter live ranges, which can
// lead to less register pressure. It can also cause instructions to be
// executed less often because they could be moved into one path of a selection
// construct.
// This optimization can cause register pressure to rise if the operands of the
// instructions go dead after the instructions being moved. That is why we only
// move certain OpLoad and OpAccessChain instructions. They generally have
// constants, loop induction variables, and global pointers as operands. The
// operands are live for a longer time in most cases.
class CodeSinkingPass : public Pass {
const char* name() const override { return "code-sink"; }
Status Process() override;
// Return the mask of preserved Analyses.
IRContext::Analysis GetPreservedAnalyses() override {
return IRContext::kAnalysisDefUse |
IRContext::kAnalysisInstrToBlockMapping |
IRContext::kAnalysisCombinators | IRContext::kAnalysisCFG |
IRContext::kAnalysisDominatorAnalysis |
IRContext::kAnalysisLoopAnalysis | IRContext::kAnalysisNameMap |
IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
// Sinks the instructions in |bb| as much as possible. Returns true if
// something changes.
bool SinkInstructionsInBB(BasicBlock* bb);
// Tries the sink |inst| as much as possible. Returns true if the instruction
// is moved.
bool SinkInstruction(Instruction* inst);
// Returns the basic block in which to move |inst| to move is as close as
// possible to the uses of |inst| without increasing the number of times
// |inst| will be executed. Return |nullptr| if there is no need to move
// |inst|.
BasicBlock* FindNewBasicBlockFor(Instruction* inst);
// Return true if |inst| reference memory and it is possible that the data in
// the memory changes at some point.
bool ReferencesMutableMemory(Instruction* inst);
// Returns true if the module contains an instruction that has a memory
// semantics id as an operand, and the memory semantics enforces a
// synchronization of uniform memory. See section 3.25 of the SPIR-V
// specification.
bool HasUniformMemorySync();
// Returns true if there may be a store to the variable |var_inst|.
bool HasPossibleStore(Instruction* var_inst);
// Returns true if one of the basic blocks in |set| exists on a path from the
// basic block |start| to |end|.
bool IntersectsPath(uint32_t start, uint32_t end,
const std::unordered_set<uint32_t>& set);
// Returns true if |mem_semantics_id| is the id of a constant that, when
// interpreted as a memory semantics mask enforces synchronization of uniform
// memory. See section 3.25 of the SPIR-V specification.
bool IsSyncOnUniform(uint32_t mem_semantics_id) const;
// True if a check has for uniform storage has taken place.
bool checked_for_uniform_sync_;
// Cache of whether or not the module has a memory sync on uniform storage.
// only valid if |check_for_uniform_sync_| is true.
bool has_uniform_sync_;
} // namespace opt
} // namespace spvtools