SPIRV-Tools/source/opt/local_single_block_elim_pass.h

// Copyright (c) 2017 The Khronos Group Inc.
// Copyright (c) 2017 Valve Corporation
// Copyright (c) 2017 LunarG Inc.
//
// 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 LIBSPIRV_OPT_LOCAL_SINGLE_BLOCK_ELIM_PASS_H_
#define LIBSPIRV_OPT_LOCAL_SINGLE_BLOCK_ELIM_PASS_H_


#include <algorithm>
#include <map>
#include <queue>
#include <utility>
#include <unordered_map>
#include <unordered_set>

#include "basic_block.h"
#include "def_use_manager.h"
#include "module.h"
#include "pass.h"

namespace spvtools {
namespace opt {

// See optimizer.hpp for documentation.
class LocalSingleBlockLoadStoreElimPass : public Pass {
 public:
  LocalSingleBlockLoadStoreElimPass();
  const char* name() const override { return "eliminate-local-single-block"; }
  Status Process(ir::Module*) override;

 private:
  // Returns true if |opcode| is a non-ptr access chain op
  bool IsNonPtrAccessChain(const SpvOp opcode) const;

  // Returns true if |typeInst| is a scalar type
  // or a vector or matrix
  bool IsMathType(const ir::Instruction* typeInst) const;

  // Returns true if |typeInst| is a math type or a struct or array
  // of a math type.
  bool IsTargetType(const ir::Instruction* typeInst) const;

  // Given a load or store |ip|, return the pointer instruction.
  // Also return the base variable's id in |varId|.
  ir::Instruction* GetPtr(ir::Instruction* ip, uint32_t* varId);

  // Return true if |varId| is a previously identified target variable.
  // Return false if |varId| is a previously identified non-target variable.
  // If variable is not cached, return true if variable is a function scope 
  // variable of target type, false otherwise. Updates caches of target 
  // and non-target variables.
  bool IsTargetVar(uint32_t varId);

  // Replace all instances of |loadInst|'s id with |replId| and delete
  // |loadInst|.
  void ReplaceAndDeleteLoad(ir::Instruction* loadInst, uint32_t replId);

  // Return true if any instruction loads from |ptrId|
  bool HasLoads(uint32_t ptrId) const;

  // Return true if |varId| is not a function variable or if it has
  // a load
  bool IsLiveVar(uint32_t varId) const;

  // Return true if |storeInst| is not to function variable or if its
  // base variable has a load
  bool IsLiveStore(ir::Instruction* storeInst);

  // Add stores using |ptr_id| to |insts|
  void AddStores(uint32_t ptr_id, std::queue<ir::Instruction*>* insts);

  // Delete |inst| and iterate DCE on all its operands. Won't delete
  // labels. 
  void DCEInst(ir::Instruction* inst);

  // On all entry point functions, within each basic block, eliminate
  // loads and stores to function variables where possible. For
  // loads, if previous load or store to same variable, replace
  // load id with previous id and delete load. Finally, check if
  // remaining stores are useless, and delete store and variable
  // where possible. Assumes logical addressing.
  bool LocalSingleBlockLoadStoreElim(ir::Function* func);

  // Save next available id into |module|.
  inline void FinalizeNextId(ir::Module* module) {
    module->SetIdBound(next_id_);
  }

  // Return next available id and calculate next.
  inline uint32_t TakeNextId() {
    return next_id_++;
  }

  void Initialize(ir::Module* module);
  Pass::Status ProcessImpl();

  // Module this pass is processing
  ir::Module* module_;

  // Def-Uses for the module we are processing
  std::unique_ptr<analysis::DefUseManager> def_use_mgr_;

  // Map from function's result id to function
  std::unordered_map<uint32_t, ir::Function*> id2function_;

  // Cache of previously seen target types
  std::unordered_set<uint32_t> seen_target_vars_;

  // Cache of previously seen non-target types
  std::unordered_set<uint32_t> seen_non_target_vars_;

  // Map from function scope variable to a store of that variable in the
  // current block whose value is currently valid. This map is cleared
  // at the start of each block and incrementally updated as the block
  // is scanned. The stores are candidates for elimination. The map is
  // conservatively cleared when a function call is encountered.
  std::unordered_map<uint32_t, ir::Instruction*> var2store_;

  // Map from function scope variable to a load of that variable in the
  // current block whose value is currently valid. This map is cleared
  // at the start of each block and incrementally updated as the block
  // is scanned. The stores are candidates for elimination. The map is
  // conservatively cleared when a function call is encountered.
  std::unordered_map<uint32_t, ir::Instruction*> var2load_;

  // Set of variables whose most recent store in the current block cannot be
  // deleted, for example, if there is a load of the variable which is
  // dependent on the store and is not replaced and deleted by this pass,
  // for example, a load through an access chain. A variable is removed
  // from this set each time a new store of that variable is encountered.
  std::unordered_set<uint32_t> pinned_vars_;

  // Next unused ID
  uint32_t next_id_;
};

}  // namespace opt
}  // namespace spvtools

#endif  // LIBSPIRV_OPT_LOCAL_SINGLE_BLOCK_ELIM_PASS_H_