SPIRV-Tools/source/opt/dead_branch_elim_pass.h
Steven Perron c2013e248b
Make the constant and type manager analyses. (#2250)
Currently it is impossible to invalidate the constnat and type manager.
However, the compact ids pass changes the ids for the types and
constants, which makes them invalid.  This change will make them
analyses that have to been explicitly marked as preserved by passes.
This will allow compact ids to invalidate them.

Fixes #2220.
2018-12-20 18:00:05 +00:00

157 lines
6.7 KiB
C++

// 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_DEAD_BRANCH_ELIM_PASS_H_
#define SOURCE_OPT_DEAD_BRANCH_ELIM_PASS_H_
#include <algorithm>
#include <map>
#include <queue>
#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"
namespace spvtools {
namespace opt {
// See optimizer.hpp for documentation.
class DeadBranchElimPass : public MemPass {
using cbb_ptr = const BasicBlock*;
public:
DeadBranchElimPass() = default;
const char* name() const override { return "eliminate-dead-branches"; }
Status Process() override;
IRContext::Analysis GetPreservedAnalyses() override {
return IRContext::kAnalysisDefUse |
IRContext::kAnalysisInstrToBlockMapping |
IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
}
private:
// If |condId| is boolean constant, return conditional value in |condVal| and
// return true, otherwise return false.
bool GetConstCondition(uint32_t condId, bool* condVal);
// If |valId| is a 32-bit integer constant, return value via |value| and
// return true, otherwise return false.
bool GetConstInteger(uint32_t valId, uint32_t* value);
// Add branch to |labelId| to end of block |bp|.
void AddBranch(uint32_t labelId, BasicBlock* bp);
// For function |func|, look for BranchConditionals with constant condition
// and convert to a Branch to the indicated label. Delete resulting dead
// blocks. Note some such branches and blocks may be left to avoid creating
// invalid control flow.
// TODO(greg-lunarg): Remove remaining constant conditional branches and dead
// blocks.
bool EliminateDeadBranches(Function* func);
// Returns the basic block containing |id|.
// Note: this pass only requires correct instruction block mappings for the
// input. This pass does not preserve the block mapping, so it is not kept
// up-to-date during processing.
BasicBlock* GetParentBlock(uint32_t id);
// Marks live blocks reachable from the entry of |func|. Simplifies constant
// branches and switches as it proceeds, to limit the number of live blocks.
// It is careful not to eliminate backedges even if they are dead, but the
// header is live. Likewise, unreachable merge blocks named in live merge
// instruction must be retained (though they may be clobbered).
bool MarkLiveBlocks(Function* func,
std::unordered_set<BasicBlock*>* live_blocks);
// Checks for unreachable merge and continue blocks with live headers; those
// blocks must be retained. Continues are tracked separately so that a live
// phi can be updated to take an undef value from any of its predecessors
// that are unreachable continues.
//
// |unreachable_continues| maps the id of an unreachable continue target to
// the header block that declares it.
void MarkUnreachableStructuredTargets(
const std::unordered_set<BasicBlock*>& live_blocks,
std::unordered_set<BasicBlock*>* unreachable_merges,
std::unordered_map<BasicBlock*, BasicBlock*>* unreachable_continues);
// Fix phis in reachable blocks so that only live (or unremovable) incoming
// edges are present. If the block now only has a single live incoming edge,
// remove the phi and replace its uses with its data input. If the single
// remaining incoming edge is from the phi itself, the the phi is in an
// unreachable single block loop. Either the block is dead and will be
// removed, or it's reachable from an unreachable continue target. In the
// latter case that continue target block will be collapsed into a block that
// only branches back to its header and we'll eliminate the block with the
// phi.
//
// |unreachable_continues| maps continue targets that cannot be reached to
// merge instruction that declares them.
bool FixPhiNodesInLiveBlocks(
Function* func, const std::unordered_set<BasicBlock*>& live_blocks,
const std::unordered_map<BasicBlock*, BasicBlock*>&
unreachable_continues);
// Erases dead blocks. Any block captured in |unreachable_merges| or
// |unreachable_continues| is a dead block that is required to remain due to
// a live merge instruction in the corresponding header. These blocks will
// have their instructions clobbered and will become a label and terminator.
// Unreachable merge blocks are terminated by OpUnreachable, while
// unreachable continue blocks are terminated by an unconditional branch to
// the header. Otherwise, blocks are dead if not explicitly captured in
// |live_blocks| and are totally removed.
//
// |unreachable_continues| maps continue targets that cannot be reached to
// corresponding header block that declares them.
bool EraseDeadBlocks(
Function* func, const std::unordered_set<BasicBlock*>& live_blocks,
const std::unordered_set<BasicBlock*>& unreachable_merges,
const std::unordered_map<BasicBlock*, BasicBlock*>&
unreachable_continues);
// Reorders blocks in reachable functions so that they satisfy dominator
// block ordering rules.
void FixBlockOrder();
// Return the first branch instruction that is a conditional branch to
// |merge_block_id|. Returns |nullptr| if no such branch exists. If there are
// multiple such branches, the first one is the one that would be executed
// first when running the code. That is, the one that dominates all of the
// others.
//
// |start_block_id| must be a block whose innermost containing merge construct
// has |merge_block_id| as the merge block.
//
// |loop_merge_id| and |loop_continue_id| are the merge and continue block ids
// of the innermost loop containing |start_block_id|.
Instruction* FindFirstExitFromSelectionMerge(uint32_t start_block_id,
uint32_t merge_block_id,
uint32_t loop_merge_id,
uint32_t loop_continue_id);
};
} // namespace opt
} // namespace spvtools
#endif // SOURCE_OPT_DEAD_BRANCH_ELIM_PASS_H_