SPIRV-Tools/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 "local_single_block_elim_pass.h"

#include "iterator.h"

namespace spvtools {
namespace opt {

namespace {

const uint32_t kStoreValIdInIdx = 1;

}  // anonymous namespace

bool LocalSingleBlockLoadStoreElimPass::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 &&
                   !this->IsNonTypeDecorate(op)) {
          hasOnlySupportedRefs = false;
        }
      });
  if (hasOnlySupportedRefs) {
    supported_ref_ptrs_.insert(ptrId);
  }
  return hasOnlySupportedRefs;
}

bool LocalSingleBlockLoadStoreElimPass::LocalSingleBlockLoadStoreElim(
    ir::Function* func) {
  // Perform local store/load and load/load elimination on each block
  std::vector<ir::Instruction*> dead_instructions;
  bool modified = false;
  for (auto bi = func->begin(); bi != func->end(); ++bi) {
    var2store_.clear();
    var2load_.clear();
    pinned_vars_.clear();
    auto next = bi->begin();
    for (auto ii = next; ii != bi->end(); ii = next) {
      ++next;
      switch (ii->opcode()) {
        case SpvOpStore: {
          // Verify store variable is target type
          uint32_t varId;
          ir::Instruction* ptrInst = GetPtr(&*ii, &varId);
          if (!IsTargetVar(varId)) continue;
          if (!HasOnlySupportedRefs(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()) {
                dead_instructions.push_back(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;
          if (!HasOnlySupportedRefs(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(kStoreValIdInIdx);
            } 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
            context()->KillNamesAndDecorates(&*ii);
            context()->ReplaceAllUsesWith(ii->result_id(), replId);
            dead_instructions.push_back(&*ii);
            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;
      }
    }

    while (!dead_instructions.empty()) {
      ir::Instruction* inst = dead_instructions.back();
      dead_instructions.pop_back();
      DCEInst(inst, [&dead_instructions](ir::Instruction* other_inst) {
        auto i = std::find(dead_instructions.begin(), dead_instructions.end(),
                           other_inst);
        if (i != dead_instructions.end()) {
          dead_instructions.erase(i);
        }
      });
    }

    // Go back and delete useless stores in block
    // TODO(greg-lunarg): Consider moving DCE into separate pass
    std::vector<ir::Instruction*> dead_stores;
    for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
      if (ii->opcode() != SpvOpStore) continue;
      if (IsLiveStore(&*ii)) continue;
      dead_stores.push_back(&*ii);
    }

    while (!dead_stores.empty()) {
      ir::Instruction* inst = dead_stores.back();
      dead_stores.pop_back();
      DCEInst(inst, [&dead_stores](ir::Instruction* other_inst) {
        auto i = std::find(dead_stores.begin(), dead_stores.end(), other_inst);
        if (i != dead_stores.end()) {
          dead_stores.erase(i);
        }
      });
    }
  }
  return modified;
}

void LocalSingleBlockLoadStoreElimPass::Initialize(ir::IRContext* c) {
  InitializeProcessing(c);

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

  // Clear collections
  supported_ref_ptrs_.clear();

  // Initialize extensions whitelist
  InitExtensions();
};

bool LocalSingleBlockLoadStoreElimPass::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 LocalSingleBlockLoadStoreElimPass::ProcessImpl() {
  // Assumes logical addressing only
  if (get_module()->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;
  // If any extensions in the module are not explicitly supported,
  // return unmodified.
  if (!AllExtensionsSupported()) return Status::SuccessWithoutChange;
  // Process all entry point functions
  ProcessFunction pfn = [this](ir::Function* fp) {
    return LocalSingleBlockLoadStoreElim(fp);
  };
  bool modified = ProcessEntryPointCallTree(pfn, get_module());
  return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}

LocalSingleBlockLoadStoreElimPass::LocalSingleBlockLoadStoreElimPass() {}

Pass::Status LocalSingleBlockLoadStoreElimPass::Process(ir::IRContext* c) {
  Initialize(c);
  return ProcessImpl();
}

void LocalSingleBlockLoadStoreElimPass::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