SPIRV-Tools/source/opt/local_single_store_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 "local_single_store_elim_pass.h"

#include "cfa.h"
#include "iterator.h"
#include "latest_version_glsl_std_450_header.h"

namespace spvtools {
namespace opt {

namespace {

const uint32_t kStoreValIdInIdx = 1;
const uint32_t kVariableInitIdInIdx = 1;

}  // anonymous namespace

bool LocalSingleStoreElimPass::HasOnlySupportedRefs(uint32_t ptrId) {
  if (supported_ref_ptrs_.find(ptrId) != supported_ref_ptrs_.end()) return true;
  bool hasOnlySupportedRefs = true;
  get_def_use_mgr()->ForEachUser(
      ptrId, [this, &hasOnlySupportedRefs](ir::Instruction* user) {
        SpvOp op = user->opcode();
        if (IsNonPtrAccessChain(op) || op == SpvOpCopyObject) {
          if (!HasOnlySupportedRefs(user->result_id())) {
            hasOnlySupportedRefs = false;
          }
        } else if (op != SpvOpStore && op != SpvOpLoad && op != SpvOpName &&
                   !IsNonTypeDecorate(op)) {
          hasOnlySupportedRefs = false;
        }
      });
  if (hasOnlySupportedRefs) {
    supported_ref_ptrs_.insert(ptrId);
  }
  return hasOnlySupportedRefs;
}

void LocalSingleStoreElimPass::SingleStoreAnalyze(ir::Function* func) {
  ssa_var2store_.clear();
  non_ssa_vars_.clear();
  store2idx_.clear();
  store2blk_.clear();
  for (auto bi = func->begin(); bi != func->end(); ++bi) {
    uint32_t instIdx = 0;
    for (auto ii = bi->begin(); ii != bi->end(); ++ii, ++instIdx) {
      uint32_t varId = 0;
      ir::Instruction* ptrInst = nullptr;
      switch (ii->opcode()) {
        case SpvOpStore: {
          ptrInst = GetPtr(&*ii, &varId);
        } break;
        case SpvOpVariable: {
          // If initializer, treat like store
          if (ii->NumInOperands() > 1) {
            varId = ii->result_id();
            ptrInst = &*ii;
          }
        } break;
        default:
          break;
      }  // switch
      if (varId == 0) continue;
      // Verify variable is target type
      if (non_ssa_vars_.find(varId) != non_ssa_vars_.end()) continue;
      if (ptrInst->opcode() != SpvOpVariable) {
        non_ssa_vars_.insert(varId);
        ssa_var2store_.erase(varId);
        continue;
      }
      // Verify target type and function storage class
      if (!IsTargetVar(varId)) {
        non_ssa_vars_.insert(varId);
        continue;
      }
      if (!HasOnlySupportedRefs(varId)) {
        non_ssa_vars_.insert(varId);
        continue;
      }
      // Ignore variables with multiple stores
      if (ssa_var2store_.find(varId) != ssa_var2store_.end()) {
        non_ssa_vars_.insert(varId);
        ssa_var2store_.erase(varId);
        continue;
      }
      // Remember pointer to variable's store and it's
      // ordinal position in block
      ssa_var2store_[varId] = &*ii;
      store2idx_[&*ii] = instIdx;
      store2blk_[&*ii] = &*bi;
    }
  }
}

LocalSingleStoreElimPass::GetBlocksFunction
LocalSingleStoreElimPass::AugmentedCFGSuccessorsFunction() const {
  return [this](const ir::BasicBlock* block) {
    auto asmi = augmented_successors_map_.find(block);
    if (asmi != augmented_successors_map_.end()) return &(*asmi).second;
    auto smi = successors_map_.find(block);
    return &(*smi).second;
  };
}

LocalSingleStoreElimPass::GetBlocksFunction
LocalSingleStoreElimPass::AugmentedCFGPredecessorsFunction() const {
  return [this](const ir::BasicBlock* block) {
    auto apmi = augmented_predecessors_map_.find(block);
    if (apmi != augmented_predecessors_map_.end()) return &(*apmi).second;
    auto pmi = predecessors_map_.find(block);
    return &(*pmi).second;
  };
}

void LocalSingleStoreElimPass::CalculateImmediateDominators(
    ir::Function* func) {
  // Compute CFG
  vector<ir::BasicBlock*> ordered_blocks;
  predecessors_map_.clear();
  successors_map_.clear();
  for (auto& blk : *func) {
    ordered_blocks.push_back(&blk);
    blk.ForEachSuccessorLabel([&blk, this](uint32_t sbid) {
      successors_map_[&blk].push_back(label2block_[sbid]);
      predecessors_map_[label2block_[sbid]].push_back(&blk);
    });
  }
  // Compute Augmented CFG
  augmented_successors_map_.clear();
  augmented_predecessors_map_.clear();
  successors_map_[cfg()->pseudo_exit_block()] = {};
  predecessors_map_[cfg()->pseudo_entry_block()] = {};
  auto succ_func = [this](const ir::BasicBlock* b) {
    return &successors_map_[b];
  };
  auto pred_func = [this](const ir::BasicBlock* b) {
    return &predecessors_map_[b];
  };
  CFA<ir::BasicBlock>::ComputeAugmentedCFG(
      ordered_blocks, cfg()->pseudo_entry_block(), cfg()->pseudo_exit_block(),
      &augmented_successors_map_, &augmented_predecessors_map_, succ_func,
      pred_func);
  // Compute Dominators
  vector<const ir::BasicBlock*> postorder;
  auto ignore_block = [](cbb_ptr) {};
  auto ignore_edge = [](cbb_ptr, cbb_ptr) {};
  spvtools::CFA<ir::BasicBlock>::DepthFirstTraversal(
      ordered_blocks[0], AugmentedCFGSuccessorsFunction(), ignore_block,
      [&](cbb_ptr b) { postorder.push_back(b); }, ignore_edge);
  auto edges = spvtools::CFA<ir::BasicBlock>::CalculateDominators(
      postorder, AugmentedCFGPredecessorsFunction());
  idom_.clear();
  for (auto edge : edges) idom_[edge.first] = edge.second;
}

bool LocalSingleStoreElimPass::Dominates(ir::BasicBlock* blk0, uint32_t idx0,
                                         ir::BasicBlock* blk1, uint32_t idx1) {
  if (blk0 == blk1) return idx0 <= idx1;
  ir::BasicBlock* b = blk1;
  while (idom_[b] != b) {
    b = idom_[b];
    if (b == blk0) return true;
  }
  return false;
}

bool LocalSingleStoreElimPass::SingleStoreProcess(ir::Function* func) {
  CalculateImmediateDominators(func);
  bool modified = false;
  for (auto bi = func->begin(); bi != func->end(); ++bi) {
    uint32_t instIdx = 0;
    std::vector<ir::Instruction*> dead_instructions;
    for (auto ii = bi->begin(); ii != bi->end(); ++ii, ++instIdx) {
      if (ii->opcode() != SpvOpLoad) continue;
      uint32_t varId;
      ir::Instruction* ptrInst = GetPtr(&*ii, &varId);
      // Skip access chain loads
      if (ptrInst->opcode() != SpvOpVariable) continue;
      const auto vsi = ssa_var2store_.find(varId);
      if (vsi == ssa_var2store_.end()) continue;
      if (non_ssa_vars_.find(varId) != non_ssa_vars_.end()) continue;
      // store must dominate load
      if (!Dominates(store2blk_[vsi->second], store2idx_[vsi->second], &*bi,
                     instIdx))
        continue;
      // Determine replacement id depending on OpStore or OpVariable
      uint32_t replId;
      if (vsi->second->opcode() == SpvOpStore)
        replId = vsi->second->GetSingleWordInOperand(kStoreValIdInIdx);
      else
        replId = vsi->second->GetSingleWordInOperand(kVariableInitIdInIdx);
      // Replace all instances of the load's id with the SSA value's id
      // and add load to removal list
      context()->KillNamesAndDecorates(&*ii);
      context()->ReplaceAllUsesWith(ii->result_id(), replId);
      dead_instructions.push_back(&*ii);
      modified = true;
    }

    // Define the function that will update the data structures as instructions
    // are deleted.
    auto update_function = [&dead_instructions,
                            this](ir::Instruction* other_inst) {
      // Update dead_instructions.
      auto i = std::find(dead_instructions.begin(), dead_instructions.end(),
                         other_inst);
      if (i != dead_instructions.end()) {
        dead_instructions.erase(i);
      }

      // Update the variable-to-store map if any of its members is DCE'd.
      uint32_t id;
      if (other_inst->opcode() == SpvOpStore) GetPtr(other_inst, &id);
      if (other_inst->opcode() == SpvOpVariable)
        id = other_inst->result_id();
      else
        return;

      auto store = ssa_var2store_.find(id);
      if (store != ssa_var2store_.end()) {
        ssa_var2store_.erase(store);
      }
    };

    while (!dead_instructions.empty()) {
      ir::Instruction* inst = dead_instructions.back();
      dead_instructions.pop_back();
      DCEInst(inst, update_function);
    }
  }
  return modified;
}

bool LocalSingleStoreElimPass::SingleStoreDCE() {
  bool modified = false;
  std::unordered_set<ir::Instruction*> already_deleted;
  for (auto v : ssa_var2store_) {
    // check that it hasn't already been DCE'd
    if (already_deleted.find(v.second) != already_deleted.end()) continue;
    if (non_ssa_vars_.find(v.first) != non_ssa_vars_.end()) continue;
    if (!IsLiveVar(v.first)) {
      DCEInst(v.second, [&already_deleted](ir::Instruction* inst) {
        already_deleted.insert(inst);
      });
      modified = true;
    }
  }
  return modified;
}

bool LocalSingleStoreElimPass::LocalSingleStoreElim(ir::Function* func) {
  bool modified = false;
  SingleStoreAnalyze(func);
  if (ssa_var2store_.empty()) return false;
  modified |= SingleStoreProcess(func);
  modified |= SingleStoreDCE();
  return modified;
}

void LocalSingleStoreElimPass::Initialize(ir::IRContext* irContext) {
  InitializeProcessing(irContext);

  // Initialize function and block maps
  label2block_.clear();
  for (auto& fn : *get_module()) {
    for (auto& blk : fn) {
      uint32_t bid = blk.id();
      label2block_[bid] = &blk;
    }
  }

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

  // Initialize Supported Ref Pointer Cache
  supported_ref_ptrs_.clear();

  // Initialize extension whitelist
  InitExtensions();
};

bool LocalSingleStoreElimPass::AllExtensionsSupported() const {
  // If any extension not in whitelist, return false
  for (auto& ei : get_module()->extensions()) {
    const char* extName =
        reinterpret_cast<const char*>(&ei.GetInOperand(0).words[0]);
    if (extensions_whitelist_.find(extName) == extensions_whitelist_.end())
      return false;
  }
  return true;
}

Pass::Status LocalSingleStoreElimPass::ProcessImpl() {
  // Assumes relaxed logical addressing only (see instruction.h)
  if (context()->get_feature_mgr()->HasCapability(SpvCapabilityAddresses))
    return Status::SuccessWithoutChange;
  // Do not process if module contains OpGroupDecorate. Additional
  // support required in KillNamesAndDecorates().
  // TODO(greg-lunarg): Add support for OpGroupDecorate
  for (auto& ai : get_module()->annotations())
    if (ai.opcode() == SpvOpGroupDecorate) return Status::SuccessWithoutChange;
  // Do not process if any disallowed extensions are enabled
  if (!AllExtensionsSupported()) return Status::SuccessWithoutChange;
  // Process all entry point functions
  ProcessFunction pfn = [this](ir::Function* fp) {
    return LocalSingleStoreElim(fp);
  };
  bool modified = ProcessEntryPointCallTree(pfn, get_module());
  return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}

LocalSingleStoreElimPass::LocalSingleStoreElimPass() {}

Pass::Status LocalSingleStoreElimPass::Process(ir::IRContext* irContext) {
  Initialize(irContext);
  return ProcessImpl();
}

void LocalSingleStoreElimPass::InitExtensions() {
  extensions_whitelist_.clear();
  extensions_whitelist_.insert({
      "SPV_AMD_shader_explicit_vertex_parameter",
      "SPV_AMD_shader_trinary_minmax",
      "SPV_AMD_gcn_shader",
      "SPV_KHR_shader_ballot",
      "SPV_AMD_shader_ballot",
      "SPV_AMD_gpu_shader_half_float",
      "SPV_KHR_shader_draw_parameters",
      "SPV_KHR_subgroup_vote",
      "SPV_KHR_16bit_storage",
      "SPV_KHR_device_group",
      "SPV_KHR_multiview",
      "SPV_NVX_multiview_per_view_attributes",
      "SPV_NV_viewport_array2",
      "SPV_NV_stereo_view_rendering",
      "SPV_NV_sample_mask_override_coverage",
      "SPV_NV_geometry_shader_passthrough",
      "SPV_AMD_texture_gather_bias_lod",
      "SPV_KHR_storage_buffer_storage_class",
      // SPV_KHR_variable_pointers
      //   Currently do not support extended pointer expressions
      "SPV_AMD_gpu_shader_int16",
      "SPV_KHR_post_depth_coverage",
      "SPV_KHR_shader_atomic_counter_ops",
  });
}

}  // namespace opt
}  // namespace spvtools