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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
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SOURCE_OPT_CODE_SINK_H_
+#define SOURCE_OPT_CODE_SINK_H_
+
+#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 {
+ public:
+ 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;
+ }
+
+ private:
+ // 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
+
+#endif // SOURCE_OPT_CODE_SINK_H_