118 lines
4.5 KiB
C++
118 lines
4.5 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_CCP_PASS_H_
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#define SOURCE_OPT_CCP_PASS_H_
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#include <memory>
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#include <unordered_map>
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#include "source/opt/constants.h"
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#include "source/opt/function.h"
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#include "source/opt/ir_context.h"
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#include "source/opt/mem_pass.h"
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#include "source/opt/module.h"
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#include "source/opt/propagator.h"
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namespace spvtools {
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namespace opt {
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class CCPPass : public MemPass {
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public:
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CCPPass() = default;
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const char* name() const override { return "ccp"; }
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Status Process() override;
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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::kAnalysisDecorations | IRContext::kAnalysisCombinators |
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IRContext::kAnalysisCFG | IRContext::kAnalysisDominatorAnalysis |
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IRContext::kAnalysisNameMap | IRContext::kAnalysisConstants |
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IRContext::kAnalysisTypes;
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}
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private:
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// Initializes the pass.
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void Initialize();
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// Runs constant propagation on the given function |fp|. Returns true if any
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// constants were propagated and the IR modified.
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bool PropagateConstants(Function* fp);
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// Visits a single instruction |instr|. If the instruction is a conditional
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// branch that always jumps to the same basic block, it sets the destination
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// block in |dest_bb|.
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SSAPropagator::PropStatus VisitInstruction(Instruction* instr,
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BasicBlock** dest_bb);
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// Visits an OpPhi instruction |phi|. This applies the meet operator for the
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// CCP lattice. Essentially, if all the operands in |phi| have the same
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// constant value C, the result for |phi| gets assigned the value C.
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SSAPropagator::PropStatus VisitPhi(Instruction* phi);
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// Visits an SSA assignment instruction |instr|. If the RHS of |instr| folds
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// into a constant value C, then the LHS of |instr| is assigned the value C in
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// |values_|.
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SSAPropagator::PropStatus VisitAssignment(Instruction* instr);
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// Visits a branch instruction |instr|. If the branch is conditional
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// (OpBranchConditional or OpSwitch), and the value of its selector is known,
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// |dest_bb| will be set to the corresponding destination block. Unconditional
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// branches always set |dest_bb| to the single destination block.
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SSAPropagator::PropStatus VisitBranch(Instruction* instr,
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BasicBlock** dest_bb) const;
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// Replaces all operands used in |fp| with the corresponding constant values
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// in |values_|. Returns true if any operands were replaced, and false
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// otherwise.
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bool ReplaceValues();
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// Marks |instr| as varying by registering a varying value for its result
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// into the |values_| table. Returns SSAPropagator::kVarying.
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SSAPropagator::PropStatus MarkInstructionVarying(Instruction* instr);
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// Returns true if |id| is the special SSA id that corresponds to a varying
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// value.
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bool IsVaryingValue(uint32_t id) const;
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// Constant manager for the parent IR context. Used to record new constants
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// generated during propagation.
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analysis::ConstantManager* const_mgr_;
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// Constant value table. Each entry <id, const_decl_id> in this map
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// represents the compile-time constant value for |id| as declared by
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// |const_decl_id|. Each |const_decl_id| in this table is an OpConstant
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// declaration for the current module.
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//
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// Additionally, this table keeps track of SSA IDs with varying values. If an
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// SSA ID is found to have a varying value, it will have an entry in this
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// table that maps to the special SSA id kVaryingSSAId. These values are
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// never replaced in the IR, they are used by CCP during propagation.
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std::unordered_map<uint32_t, uint32_t> values_;
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// Propagator engine used.
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std::unique_ptr<SSAPropagator> propagator_;
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// Value for the module's ID bound before running CCP. Used to detect whether
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// propagation created new instructions.
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uint32_t original_id_bound_;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_CCP_PASS_H_
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