source/opt/local_single_block_elim_pass.cpp

// 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.

#include "iterator.h"
#include "local_single_block_elim_pass.h"

static const int kSpvEntryPointFunctionId = 1;
static const int kSpvStorePtrId = 0;
static const int kSpvStoreValId = 1;
static const int kSpvLoadPtrId = 0;
static const int kSpvAccessChainPtrId = 0;
static const int kSpvTypePointerStorageClass = 0;
static const int kSpvTypePointerTypeId = 1;

namespace spvtools {
namespace opt {

bool LocalSingleBlockLoadStoreElimPass::IsNonPtrAccessChain(
    const SpvOp opcode) const {
  return opcode == SpvOpAccessChain || opcode == SpvOpInBoundsAccessChain;
}

bool LocalSingleBlockLoadStoreElimPass::IsMathType(
    const ir::Instruction* typeInst) const {
  switch (typeInst->opcode()) {
  case SpvOpTypeInt:
  case SpvOpTypeFloat:
  case SpvOpTypeBool:
  case SpvOpTypeVector:
  case SpvOpTypeMatrix:
    return true;
  default:
    break;
  }
  return false;
}

bool LocalSingleBlockLoadStoreElimPass::IsTargetType(
    const ir::Instruction* typeInst) const {
  if (IsMathType(typeInst))
    return true;
  if (typeInst->opcode() == SpvOpTypeArray)
    return IsMathType(def_use_mgr_->GetDef(typeInst->GetSingleWordOperand(1)));
  if (typeInst->opcode() != SpvOpTypeStruct)
    return false;
  // All struct members must be math type
  int nonMathComp = 0;
  typeInst->ForEachInId([&nonMathComp,this](const uint32_t* tid) {
    ir::Instruction* compTypeInst = def_use_mgr_->GetDef(*tid);
    if (!IsMathType(compTypeInst)) ++nonMathComp;
  });
  return nonMathComp == 0;
}

ir::Instruction* LocalSingleBlockLoadStoreElimPass::GetPtr(
      ir::Instruction* ip, uint32_t* varId) {
  *varId = ip->GetSingleWordInOperand(
      ip->opcode() == SpvOpStore ?  kSpvStorePtrId : kSpvLoadPtrId);
  ir::Instruction* ptrInst = def_use_mgr_->GetDef(*varId);
  ir::Instruction* varInst = ptrInst;
  while (IsNonPtrAccessChain(varInst->opcode())) {
    *varId = varInst->GetSingleWordInOperand(kSpvAccessChainPtrId);
    varInst = def_use_mgr_->GetDef(*varId);
  }
  return ptrInst;
}

bool LocalSingleBlockLoadStoreElimPass::IsTargetVar(uint32_t varId) {
  if (seen_non_target_vars_.find(varId) != seen_non_target_vars_.end())
    return false;
  if (seen_target_vars_.find(varId) != seen_target_vars_.end())
    return true;
  const ir::Instruction* varInst = def_use_mgr_->GetDef(varId);
  assert(varInst->opcode() == SpvOpVariable);
  const uint32_t varTypeId = varInst->type_id();
  const ir::Instruction* varTypeInst = def_use_mgr_->GetDef(varTypeId);
  if (varTypeInst->GetSingleWordInOperand(kSpvTypePointerStorageClass) !=
    SpvStorageClassFunction) {
    seen_non_target_vars_.insert(varId);
    return false;
  }
  const uint32_t varPteTypeId =
    varTypeInst->GetSingleWordInOperand(kSpvTypePointerTypeId);
  ir::Instruction* varPteTypeInst = def_use_mgr_->GetDef(varPteTypeId);
  if (!IsTargetType(varPteTypeInst)) {
    seen_non_target_vars_.insert(varId);
    return false;
  }
  seen_target_vars_.insert(varId);
  return true;
}

void LocalSingleBlockLoadStoreElimPass::ReplaceAndDeleteLoad(
    ir::Instruction* loadInst, uint32_t replId) {
  const uint32_t loadId = loadInst->result_id();
  (void) def_use_mgr_->ReplaceAllUsesWith(loadId, replId);
  // TODO(greg-lunarg): Consider moving DCE into separate pass
  DCEInst(loadInst);
}

bool LocalSingleBlockLoadStoreElimPass::HasLoads(uint32_t ptrId) const {
  analysis::UseList* uses = def_use_mgr_->GetUses(ptrId);
  if (uses == nullptr)
    return false;
  for (auto u : *uses) {
    SpvOp op = u.inst->opcode();
    if (IsNonPtrAccessChain(op)) {
      if (HasLoads(u.inst->result_id()))
        return true;
    }
    else {
      // Conservatively assume that calls will do a load
      // TODO(): Improve analysis around function calls
      if (op == SpvOpLoad || op == SpvOpFunctionCall)
        return true;
    }
  }
  return false;
}

bool LocalSingleBlockLoadStoreElimPass::IsLiveVar(uint32_t varId) const {
  // non-function scope vars are live
  const ir::Instruction* varInst = def_use_mgr_->GetDef(varId);
  assert(varInst->opcode() == SpvOpVariable);
  const uint32_t varTypeId = varInst->type_id();
  const ir::Instruction* varTypeInst = def_use_mgr_->GetDef(varTypeId);
  if (varTypeInst->GetSingleWordInOperand(kSpvTypePointerStorageClass) !=
      SpvStorageClassFunction)
    return true;
  // test if variable is loaded from
  return HasLoads(varId);
}

bool LocalSingleBlockLoadStoreElimPass::IsLiveStore(
    ir::Instruction* storeInst) {
  // get store's variable
  uint32_t varId;
  (void) GetPtr(storeInst, &varId);
  return IsLiveVar(varId);
}

void LocalSingleBlockLoadStoreElimPass::AddStores(
    uint32_t ptr_id, std::queue<ir::Instruction*>* insts) {
  analysis::UseList* uses = def_use_mgr_->GetUses(ptr_id);
  if (uses != nullptr) {
    for (auto u : *uses) {
      if (IsNonPtrAccessChain(u.inst->opcode()))
        AddStores(u.inst->result_id(), insts);
      else if (u.inst->opcode() == SpvOpStore)
        insts->push(u.inst);
    }
  }
}

void LocalSingleBlockLoadStoreElimPass::DCEInst(ir::Instruction* inst) {
  std::queue<ir::Instruction*> deadInsts;
  deadInsts.push(inst);
  while (!deadInsts.empty()) {
    ir::Instruction* di = deadInsts.front();
    // Don't delete labels
    if (di->opcode() == SpvOpLabel) {
      deadInsts.pop();
      continue;
    }
    // Remember operands
    std::vector<uint32_t> ids;
    di->ForEachInId([&ids](uint32_t* iid) {
      ids.push_back(*iid);
    });
    uint32_t varId = 0;
    // Remember variable if dead load
    if (di->opcode() == SpvOpLoad)
      (void) GetPtr(di, &varId);
    def_use_mgr_->KillInst(di);
    // For all operands with no remaining uses, add their instruction
    // to the dead instruction queue.
    for (auto id : ids) {
      analysis::UseList* uses = def_use_mgr_->GetUses(id);
      if (uses == nullptr)
        deadInsts.push(def_use_mgr_->GetDef(id));
    }
    // if a load was deleted and it was the variable's
    // last load, add all its stores to dead queue
    if (varId != 0 && !IsLiveVar(varId)) 
      AddStores(varId, &deadInsts);
    deadInsts.pop();
  }
}

bool LocalSingleBlockLoadStoreElimPass::LocalSingleBlockLoadStoreElim(
    ir::Function* func) {
  // Verify no CopyObject ops in function. This is a pre-SSA pass and
  // is generally not useful for code already in CSSA form.
  for (auto& blk : *func)
    for (auto& inst : blk)
      if (inst.opcode() == SpvOpCopyObject)
        return false;
  // Perform local store/load and load/load elimination on each block
  bool modified = false;
  for (auto bi = func->begin(); bi != func->end(); ++bi) {
    var2store_.clear();
    var2load_.clear();
    pinned_vars_.clear();
    for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
      switch (ii->opcode()) {
      case SpvOpStore: {
        // Verify store variable is target type
        uint32_t varId;
        ir::Instruction* ptrInst = GetPtr(&*ii, &varId);
        if (!IsTargetVar(varId))
          continue;
        // Register the store
        if (ptrInst->opcode() == SpvOpVariable) {
          // if not pinned, look for WAW
          if (pinned_vars_.find(varId) == pinned_vars_.end()) {
            auto si = var2store_.find(varId);
            if (si != var2store_.end()) {
              def_use_mgr_->KillInst(si->second);
            }
          }
          var2store_[varId] = &*ii;
        }
        else {
          assert(IsNonPtrAccessChain(ptrInst->opcode()));
          var2store_.erase(varId);
        }
        pinned_vars_.erase(varId);
        var2load_.erase(varId);
      } break;
      case SpvOpLoad: {
        // Verify store variable is target type
        uint32_t varId;
        ir::Instruction* ptrInst = GetPtr(&*ii, &varId);
        if (!IsTargetVar(varId))
          continue;
        // Look for previous store or load
        uint32_t replId = 0;
        if (ptrInst->opcode() == SpvOpVariable) {
          auto si = var2store_.find(varId);
          if (si != var2store_.end()) {
            replId = si->second->GetSingleWordInOperand(kSpvStoreValId);
          }
          else {
            auto li = var2load_.find(varId);
            if (li != var2load_.end()) {
              replId = li->second->result_id();
            }
          }
        }
        if (replId != 0) {
          // replace load's result id and delete load
          ReplaceAndDeleteLoad(&*ii, replId);
          modified = true;
        }
        else {
          if (ptrInst->opcode() == SpvOpVariable)
            var2load_[varId] = &*ii;  // register load
          pinned_vars_.insert(varId);
        }
      } break;
      case SpvOpFunctionCall: {
        // Conservatively assume all locals are redefined for now.
        // TODO(): Handle more optimally
        var2store_.clear();
        var2load_.clear();
        pinned_vars_.clear();
      } break;
      default:
        break;
      }
    }
    // Go back and delete useless stores in block
    // TODO(greg-lunarg): Consider moving DCE into separate pass
    for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
      if (ii->opcode() != SpvOpStore)
        continue;
      if (IsLiveStore(&*ii))
        continue;
      DCEInst(&*ii);
    }
  }
  return modified;
}

void LocalSingleBlockLoadStoreElimPass::Initialize(ir::Module* module) {

  module_ = module;

  // Initialize function and block maps
  id2function_.clear();
  for (auto& fn : *module_) 
    id2function_[fn.result_id()] = &fn;

  // Initialize Target Type Caches
  seen_target_vars_.clear();
  seen_non_target_vars_.clear();

  // TODO(): Reuse def/use from previous passes
  def_use_mgr_.reset(new analysis::DefUseManager(consumer(), module_));

  // Start new ids with next availablein module
  next_id_ = module_->id_bound();

};

Pass::Status LocalSingleBlockLoadStoreElimPass::ProcessImpl() {
  // Assumes logical addressing only
  if (module_->HasCapability(SpvCapabilityAddresses))
    return Status::SuccessWithoutChange;
  bool modified = false;
  // Call Mem2Reg on all remaining functions.
  for (auto& e : module_->entry_points()) {
    ir::Function* fn =
        id2function_[e.GetSingleWordOperand(kSpvEntryPointFunctionId)];
    modified = modified || LocalSingleBlockLoadStoreElim(fn);
  }
  FinalizeNextId(module_);
  return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}

LocalSingleBlockLoadStoreElimPass::LocalSingleBlockLoadStoreElimPass()
    : module_(nullptr), def_use_mgr_(nullptr), next_id_(0) {}

Pass::Status LocalSingleBlockLoadStoreElimPass::Process(ir::Module* module) {
  Initialize(module);
  return ProcessImpl();
}

}  // namespace opt
}  // namespace spvtools