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// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#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*;
using GetBlocksFunction =
std::function<std::vector<BasicBlock*>*(const BasicBlock*)>;
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;
// 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())) {
// 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);
// If |bp| is structured header block, returns true and sets |mergeInst| to
// the merge instruction, |branchInst| to the branch and |mergeBlockId| to the
// merge block if they are not nullptr. Any of |mergeInst|, |branchInst| or
// |mergeBlockId| may be a null pointer. Returns false if |bp| is a null
// pointer.
bool IsStructuredHeader(BasicBlock* bp, Instruction** mergeInst,
Instruction** branchInst, uint32_t* mergeBlockId);
// Initialize block2headerBranch_, header2nextHeaderBranch_, and
// branch2merge_ using |structuredOrder| to order blocks.
void ComputeBlock2HeaderMaps(std::list<BasicBlock*>& structuredOrder);
// 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();
// True if current function has a call instruction contained in it
bool call_in_func_;
// True if current function is an entry point
bool func_is_entry_point_;
// 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_;
// Map from block to the branch instruction in the header of the most
// immediate controlling structured if or loop. A loop header block points
// to its own branch instruction. An if-selection block points to the branch
// of an enclosing construct's header, if one exists.
std::unordered_map<BasicBlock*, Instruction*> block2headerBranch_;
// Map from header block to the branch instruction in the header of the
// structured construct enclosing it.
// The liveness algorithm is designed to iteratively mark as live all
// structured constructs enclosing a live instruction.
std::unordered_map<BasicBlock*, Instruction*> header2nextHeaderBranch_;
// Maps basic block to their index in the structured order traversal.
std::unordered_map<BasicBlock*, uint32_t> structured_order_index_;
// Map from branch to its associated merge instruction, if any
std::unordered_map<Instruction*, Instruction*> branch2merge_;
// Store instructions to variables of private storage
std::vector<Instruction*> private_stores_;
// 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