// 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 SOURCE_OPT_AGGRESSIVE_DEAD_CODE_ELIM_PASS_H_
#define SOURCE_OPT_AGGRESSIVE_DEAD_CODE_ELIM_PASS_H_

#include <algorithm>
#include <list>
#include <map>
#include <queue>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#include "source/opt/basic_block.h"
#include "source/opt/def_use_manager.h"
#include "source/opt/mem_pass.h"
#include "source/opt/module.h"
#include "source/util/bit_vector.h"

namespace spvtools {
namespace opt {

// See optimizer.hpp for documentation.
class AggressiveDCEPass : public MemPass {
  using cbb_ptr = const BasicBlock*;

 public:
  using GetBlocksFunction =
      std::function<std::vector<BasicBlock*>*(const BasicBlock*)>;

  AggressiveDCEPass(bool preserve_interface = false)
      : preserve_interface_(preserve_interface) {}

  const char* name() const override { return "eliminate-dead-code-aggressive"; }
  Status Process() override;

  IRContext::Analysis GetPreservedAnalyses() override {
    return IRContext::kAnalysisDefUse |
           IRContext::kAnalysisInstrToBlockMapping |
           IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
  }

 private:
  // Preserve entry point interface if true. All variables in interface
  // will be marked live and will not be eliminated. This mode is needed by
  // GPU-Assisted Validation instrumentation where a change in the interface
  // is not allowed.
  bool preserve_interface_;

  // Return true if |varId| is a variable of |storageClass|. |varId| must either
  // be 0 or the result of an instruction.
  bool IsVarOfStorage(uint32_t varId, uint32_t storageClass);

  // Return true if |varId| is variable of function storage class or is
  // private variable and privates can be optimized like locals (see
  // privates_like_local_).
  bool IsLocalVar(uint32_t varId);

  // Return true if |inst| is marked live.
  bool IsLive(const Instruction* inst) const {
    return live_insts_.Get(inst->unique_id());
  }

  // Returns true if |inst| is dead.
  bool IsDead(Instruction* inst);

  // Adds entry points, execution modes and workgroup size decorations to the
  // worklist for processing with the first function.
  void InitializeModuleScopeLiveInstructions();

  // Add |inst| to worklist_ and live_insts_.
  void AddToWorklist(Instruction* inst) {
    if (!live_insts_.Set(inst->unique_id())) {
      worklist_.push(inst);
    }
  }

  // Add all store instruction which use |ptrId|, directly or indirectly,
  // to the live instruction worklist.
  void AddStores(Function* func, uint32_t ptrId);

  // Initialize extensions allowlist
  void InitExtensions();

  // Return true if all extensions in this module are supported by this pass.
  bool AllExtensionsSupported() const;

  // Returns true if the target of |inst| is dead.  An instruction is dead if
  // its result id is used in decoration or debug instructions only. |inst| is
  // assumed to be OpName, OpMemberName or an annotation instruction.
  bool IsTargetDead(Instruction* inst);

  // If |varId| is local, mark all stores of varId as live.
  void ProcessLoad(Function* func, uint32_t varId);

  // Add branch to |labelId| to end of block |bp|.
  void AddBranch(uint32_t labelId, BasicBlock* bp);

  // Add all break and continue branches in the construct associated with
  // |mergeInst| to worklist if not already live
  void AddBreaksAndContinuesToWorklist(Instruction* mergeInst);

  // Eliminates dead debug2 and annotation instructions. Marks dead globals for
  // removal (e.g. types, constants and variables).
  bool ProcessGlobalValues();

  // Erases functions that are unreachable from the entry points of the module.
  bool EliminateDeadFunctions();

  // For function |func|, mark all Stores to non-function-scope variables
  // and block terminating instructions as live. Recursively mark the values
  // they use. When complete, mark any non-live instructions to be deleted.
  // Returns true if the function has been modified.
  //
  // Note: This function does not delete useless control structures. All
  // existing control structures will remain. This can leave not-insignificant
  // sequences of ultimately useless code.
  // TODO(): Remove useless control constructs.
  bool AggressiveDCE(Function* func);

  Pass::Status ProcessImpl();

  // Adds instructions which must be kept because of they have side-effects
  // that ADCE cannot model to the work list.
  void InitializeWorkList(Function* func,
                          std::list<BasicBlock*>& structuredOrder);

  // Marks all of the OpFunctionParameter instructions in |func| as live.
  void MarkFunctionParameterAsLive(const Function* func);

  // Returns the terminator instruction in the header for the innermost
  // construct that contains |blk|.  Returns nullptr if no such header exists.
  Instruction* GetHeaderBranch(BasicBlock* blk);

  // Returns the header for the innermost construct that contains |blk|.  A loop
  // header will be its own header.  Returns nullptr if no such header exists.
  BasicBlock* GetHeaderBlock(BasicBlock* blk) const;

  // Returns the same as |GetHeaderBlock| except if |blk| is a loop header it
  // will return the header of the next enclosing construct.  Returns nullptr if
  // no such header exists.
  Instruction* GetBranchForNextHeader(BasicBlock* blk);

  // Returns the merge instruction in the same basic block as |inst|.  Returns
  // nullptr if one does not exist.
  Instruction* GetMergeInstruction(Instruction* inst);

  // Returns true if |bb| is in the construct with header |header_block|.
  bool BlockIsInConstruct(BasicBlock* header_block, BasicBlock* bb);

  // True if current function is entry point and has no function calls.
  bool private_like_local_;

  // Live Instruction Worklist.  An instruction is added to this list
  // if it might have a side effect, either directly or indirectly.
  // If we don't know, then add it to this list.  Instructions are
  // removed from this list as the algorithm traces side effects,
  // building up the live instructions set |live_insts_|.
  std::queue<Instruction*> worklist_;

  // Live Instructions
  utils::BitVector live_insts_;

  // Live Local Variables
  std::unordered_set<uint32_t> live_local_vars_;

  // List of instructions to delete. Deletion is delayed until debug and
  // annotation instructions are processed.
  std::vector<Instruction*> to_kill_;

  // Extensions supported by this pass.
  std::unordered_set<std::string> extensions_allowlist_;
};

}  // namespace opt
}  // namespace spvtools

#endif  // SOURCE_OPT_AGGRESSIVE_DEAD_CODE_ELIM_PASS_H_
