SPIRV-Tools/source/opt/dead_insert_elim_pass.cpp
2021-10-18 13:18:16 -04:00

265 lines
10 KiB
C++

// Copyright (c) 2018 The Khronos Group Inc.
// Copyright (c) 2018 Valve Corporation
// Copyright (c) 2018 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 "source/opt/dead_insert_elim_pass.h"
#include "source/opt/composite.h"
#include "source/opt/ir_context.h"
#include "source/opt/iterator.h"
#include "spirv/1.2/GLSL.std.450.h"
namespace spvtools {
namespace opt {
namespace {
const uint32_t kTypeVectorCountInIdx = 1;
const uint32_t kTypeMatrixCountInIdx = 1;
const uint32_t kTypeArrayLengthIdInIdx = 1;
const uint32_t kTypeIntWidthInIdx = 0;
const uint32_t kConstantValueInIdx = 0;
const uint32_t kInsertObjectIdInIdx = 0;
const uint32_t kInsertCompositeIdInIdx = 1;
} // anonymous namespace
uint32_t DeadInsertElimPass::NumComponents(Instruction* typeInst) {
switch (typeInst->opcode()) {
case SpvOpTypeVector: {
return typeInst->GetSingleWordInOperand(kTypeVectorCountInIdx);
} break;
case SpvOpTypeMatrix: {
return typeInst->GetSingleWordInOperand(kTypeMatrixCountInIdx);
} break;
case SpvOpTypeArray: {
uint32_t lenId =
typeInst->GetSingleWordInOperand(kTypeArrayLengthIdInIdx);
Instruction* lenInst = get_def_use_mgr()->GetDef(lenId);
if (lenInst->opcode() != SpvOpConstant) return 0;
uint32_t lenTypeId = lenInst->type_id();
Instruction* lenTypeInst = get_def_use_mgr()->GetDef(lenTypeId);
// TODO(greg-lunarg): Support non-32-bit array length
if (lenTypeInst->GetSingleWordInOperand(kTypeIntWidthInIdx) != 32)
return 0;
return lenInst->GetSingleWordInOperand(kConstantValueInIdx);
} break;
case SpvOpTypeStruct: {
return typeInst->NumInOperands();
} break;
default: { return 0; } break;
}
}
void DeadInsertElimPass::MarkInsertChain(
Instruction* insertChain, std::vector<uint32_t>* pExtIndices,
uint32_t extOffset, std::unordered_set<uint32_t>* visited_phis) {
// Not currently optimizing array inserts.
Instruction* typeInst = get_def_use_mgr()->GetDef(insertChain->type_id());
if (typeInst->opcode() == SpvOpTypeArray) return;
// Insert chains are only composed of inserts and phis
if (insertChain->opcode() != SpvOpCompositeInsert &&
insertChain->opcode() != SpvOpPhi)
return;
// If extract indices are empty, mark all subcomponents if type
// is constant length.
if (pExtIndices == nullptr) {
uint32_t cnum = NumComponents(typeInst);
if (cnum > 0) {
std::vector<uint32_t> extIndices;
for (uint32_t i = 0; i < cnum; i++) {
extIndices.clear();
extIndices.push_back(i);
std::unordered_set<uint32_t> sub_visited_phis;
MarkInsertChain(insertChain, &extIndices, 0, &sub_visited_phis);
}
return;
}
}
Instruction* insInst = insertChain;
while (insInst->opcode() == SpvOpCompositeInsert) {
// If no extract indices, mark insert and inserted object (which might
// also be an insert chain) and continue up the chain though the input
// composite.
//
// Note: We mark inserted objects in this function (rather than in
// EliminateDeadInsertsOnePass) because in some cases, we can do it
// more accurately here.
if (pExtIndices == nullptr) {
liveInserts_.insert(insInst->result_id());
uint32_t objId = insInst->GetSingleWordInOperand(kInsertObjectIdInIdx);
std::unordered_set<uint32_t> obj_visited_phis;
MarkInsertChain(get_def_use_mgr()->GetDef(objId), nullptr, 0,
&obj_visited_phis);
// If extract indices match insert, we are done. Mark insert and
// inserted object.
} else if (ExtInsMatch(*pExtIndices, insInst, extOffset)) {
liveInserts_.insert(insInst->result_id());
uint32_t objId = insInst->GetSingleWordInOperand(kInsertObjectIdInIdx);
std::unordered_set<uint32_t> obj_visited_phis;
MarkInsertChain(get_def_use_mgr()->GetDef(objId), nullptr, 0,
&obj_visited_phis);
break;
// If non-matching intersection, mark insert
} else if (ExtInsConflict(*pExtIndices, insInst, extOffset)) {
liveInserts_.insert(insInst->result_id());
// If more extract indices than insert, we are done. Use remaining
// extract indices to mark inserted object.
uint32_t numInsertIndices = insInst->NumInOperands() - 2;
if (pExtIndices->size() - extOffset > numInsertIndices) {
uint32_t objId = insInst->GetSingleWordInOperand(kInsertObjectIdInIdx);
std::unordered_set<uint32_t> obj_visited_phis;
MarkInsertChain(get_def_use_mgr()->GetDef(objId), pExtIndices,
extOffset + numInsertIndices, &obj_visited_phis);
break;
// If fewer extract indices than insert, also mark inserted object and
// continue up chain.
} else {
uint32_t objId = insInst->GetSingleWordInOperand(kInsertObjectIdInIdx);
std::unordered_set<uint32_t> obj_visited_phis;
MarkInsertChain(get_def_use_mgr()->GetDef(objId), nullptr, 0,
&obj_visited_phis);
}
}
// Get next insert in chain
const uint32_t compId =
insInst->GetSingleWordInOperand(kInsertCompositeIdInIdx);
insInst = get_def_use_mgr()->GetDef(compId);
}
// If insert chain ended with phi, do recursive call on each operand
if (insInst->opcode() != SpvOpPhi) return;
// Mark phi visited to prevent potential infinite loop. If phi is already
// visited, return to avoid infinite loop.
if (visited_phis->count(insInst->result_id()) != 0) return;
visited_phis->insert(insInst->result_id());
// Phis may have duplicate inputs values for different edges, prune incoming
// ids lists before recursing.
std::vector<uint32_t> ids;
for (uint32_t i = 0; i < insInst->NumInOperands(); i += 2) {
ids.push_back(insInst->GetSingleWordInOperand(i));
}
std::sort(ids.begin(), ids.end());
auto new_end = std::unique(ids.begin(), ids.end());
for (auto id_iter = ids.begin(); id_iter != new_end; ++id_iter) {
Instruction* pi = get_def_use_mgr()->GetDef(*id_iter);
MarkInsertChain(pi, pExtIndices, extOffset, visited_phis);
}
}
bool DeadInsertElimPass::EliminateDeadInserts(Function* func) {
bool modified = false;
bool lastmodified = true;
// Each pass can delete dead instructions, thus potentially revealing
// new dead insertions ie insertions with no uses.
while (lastmodified) {
lastmodified = EliminateDeadInsertsOnePass(func);
modified |= lastmodified;
}
return modified;
}
bool DeadInsertElimPass::EliminateDeadInsertsOnePass(Function* func) {
bool modified = false;
liveInserts_.clear();
visitedPhis_.clear();
// Mark all live inserts
for (auto bi = func->begin(); bi != func->end(); ++bi) {
for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
// Only process Inserts and composite Phis
SpvOp op = ii->opcode();
Instruction* typeInst = get_def_use_mgr()->GetDef(ii->type_id());
if (op != SpvOpCompositeInsert &&
(op != SpvOpPhi || !spvOpcodeIsComposite(typeInst->opcode())))
continue;
// The marking algorithm can be expensive for large arrays and the
// efficacy of eliminating dead inserts into arrays is questionable.
// Skip optimizing array inserts for now. Just mark them live.
// TODO(greg-lunarg): Eliminate dead array inserts
if (op == SpvOpCompositeInsert) {
if (typeInst->opcode() == SpvOpTypeArray) {
liveInserts_.insert(ii->result_id());
continue;
}
}
const uint32_t id = ii->result_id();
get_def_use_mgr()->ForEachUser(id, [&ii, this](Instruction* user) {
if (user->IsCommonDebugInstr()) return;
switch (user->opcode()) {
case SpvOpCompositeInsert:
case SpvOpPhi:
// Use by insert or phi does not initiate marking
break;
case SpvOpCompositeExtract: {
// Capture extract indices
std::vector<uint32_t> extIndices;
uint32_t icnt = 0;
user->ForEachInOperand([&icnt, &extIndices](const uint32_t* idp) {
if (icnt > 0) extIndices.push_back(*idp);
++icnt;
});
// Mark all inserts in chain that intersect with extract
std::unordered_set<uint32_t> visited_phis;
MarkInsertChain(&*ii, &extIndices, 0, &visited_phis);
} break;
default: {
// Mark inserts in chain for all components
MarkInsertChain(&*ii, nullptr, 0, nullptr);
} break;
}
});
}
}
// Find and disconnect dead inserts
std::vector<Instruction*> dead_instructions;
for (auto bi = func->begin(); bi != func->end(); ++bi) {
for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
if (ii->opcode() != SpvOpCompositeInsert) continue;
const uint32_t id = ii->result_id();
if (liveInserts_.find(id) != liveInserts_.end()) continue;
const uint32_t replId =
ii->GetSingleWordInOperand(kInsertCompositeIdInIdx);
(void)context()->ReplaceAllUsesWith(id, replId);
dead_instructions.push_back(&*ii);
modified = true;
}
}
// DCE dead inserts
while (!dead_instructions.empty()) {
Instruction* inst = dead_instructions.back();
dead_instructions.pop_back();
DCEInst(inst, [&dead_instructions](Instruction* other_inst) {
auto i = std::find(dead_instructions.begin(), dead_instructions.end(),
other_inst);
if (i != dead_instructions.end()) {
dead_instructions.erase(i);
}
});
}
return modified;
}
Pass::Status DeadInsertElimPass::Process() {
// Process all entry point functions.
ProcessFunction pfn = [this](Function* fp) {
return EliminateDeadInserts(fp);
};
bool modified = context()->ProcessReachableCallTree(pfn);
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
} // namespace opt
} // namespace spvtools