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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
//
// 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/mem_pass.h"
#include <memory>
#include <set>
#include <vector>
#include "source/cfa.h"
#include "source/opt/basic_block.h"
#include "source/opt/dominator_analysis.h"
#include "source/opt/ir_context.h"
#include "source/opt/iterator.h"
namespace spvtools {
namespace opt {
namespace {
const uint32_t kCopyObjectOperandInIdx = 0;
const uint32_t kTypePointerStorageClassInIdx = 0;
const uint32_t kTypePointerTypeIdInIdx = 1;
} // namespace
bool MemPass::IsBaseTargetType(const Instruction* typeInst) const {
switch (typeInst->opcode()) {
case SpvOpTypeInt:
case SpvOpTypeFloat:
case SpvOpTypeBool:
case SpvOpTypeVector:
case SpvOpTypeMatrix:
case SpvOpTypeImage:
case SpvOpTypeSampler:
case SpvOpTypeSampledImage:
case SpvOpTypePointer:
return true;
default:
break;
}
return false;
}
bool MemPass::IsTargetType(const Instruction* typeInst) const {
if (IsBaseTargetType(typeInst)) return true;
if (typeInst->opcode() == SpvOpTypeArray) {
if (!IsTargetType(
get_def_use_mgr()->GetDef(typeInst->GetSingleWordOperand(1)))) {
return false;
}
return true;
}
if (typeInst->opcode() != SpvOpTypeStruct) return false;
// All struct members must be math type
return typeInst->WhileEachInId([this](const uint32_t* tid) {
Instruction* compTypeInst = get_def_use_mgr()->GetDef(*tid);
if (!IsTargetType(compTypeInst)) return false;
return true;
});
}
bool MemPass::IsNonPtrAccessChain(const SpvOp opcode) const {
return opcode == SpvOpAccessChain || opcode == SpvOpInBoundsAccessChain;
}
bool MemPass::IsPtr(uint32_t ptrId) {
uint32_t varId = ptrId;
Instruction* ptrInst = get_def_use_mgr()->GetDef(varId);
while (ptrInst->opcode() == SpvOpCopyObject) {
varId = ptrInst->GetSingleWordInOperand(kCopyObjectOperandInIdx);
ptrInst = get_def_use_mgr()->GetDef(varId);
}
const SpvOp op = ptrInst->opcode();
if (op == SpvOpVariable || IsNonPtrAccessChain(op)) return true;
if (op != SpvOpFunctionParameter) return false;
const uint32_t varTypeId = ptrInst->type_id();
const Instruction* varTypeInst = get_def_use_mgr()->GetDef(varTypeId);
return varTypeInst->opcode() == SpvOpTypePointer;
}
Instruction* MemPass::GetPtr(uint32_t ptrId, uint32_t* varId) {
*varId = ptrId;
Instruction* ptrInst = get_def_use_mgr()->GetDef(*varId);
Instruction* varInst;
if (ptrInst->opcode() == SpvOpConstantNull) {
*varId = 0;
return ptrInst;
}
if (ptrInst->opcode() != SpvOpVariable &&
ptrInst->opcode() != SpvOpFunctionParameter) {
varInst = ptrInst->GetBaseAddress();
} else {
varInst = ptrInst;
}
if (varInst->opcode() == SpvOpVariable) {
*varId = varInst->result_id();
} else {
*varId = 0;
}
while (ptrInst->opcode() == SpvOpCopyObject) {
uint32_t temp = ptrInst->GetSingleWordInOperand(0);
ptrInst = get_def_use_mgr()->GetDef(temp);
}
return ptrInst;
}
Instruction* MemPass::GetPtr(Instruction* ip, uint32_t* varId) {
assert(ip->opcode() == SpvOpStore || ip->opcode() == SpvOpLoad ||
ip->opcode() == SpvOpImageTexelPointer || ip->IsAtomicWithLoad());
// All of these opcode place the pointer in position 0.
const uint32_t ptrId = ip->GetSingleWordInOperand(0);
return GetPtr(ptrId, varId);
}
bool MemPass::HasOnlyNamesAndDecorates(uint32_t id) const {
return get_def_use_mgr()->WhileEachUser(id, [this](Instruction* user) {
SpvOp op = user->opcode();
if (op != SpvOpName && !IsNonTypeDecorate(op)) {
return false;
}
return true;
});
}
void MemPass::KillAllInsts(BasicBlock* bp, bool killLabel) {
bp->KillAllInsts(killLabel);
}
bool MemPass::HasLoads(uint32_t varId) const {
return !get_def_use_mgr()->WhileEachUser(varId, [this](Instruction* user) {
SpvOp op = user->opcode();
// TODO(): The following is slightly conservative. Could be
// better handling of non-store/name.
if (IsNonPtrAccessChain(op) || op == SpvOpCopyObject) {
if (HasLoads(user->result_id())) {
return false;
}
} else if (op != SpvOpStore && op != SpvOpName && !IsNonTypeDecorate(op)) {
return false;
}
return true;
});
}
bool MemPass::IsLiveVar(uint32_t varId) const {
const Instruction* varInst = get_def_use_mgr()->GetDef(varId);
// assume live if not a variable eg. function parameter
if (varInst->opcode() != SpvOpVariable) return true;
// non-function scope vars are live
const uint32_t varTypeId = varInst->type_id();
const Instruction* varTypeInst = get_def_use_mgr()->GetDef(varTypeId);
if (varTypeInst->GetSingleWordInOperand(kTypePointerStorageClassInIdx) !=
SpvStorageClassFunction)
return true;
// test if variable is loaded from
return HasLoads(varId);
}
void MemPass::AddStores(uint32_t ptr_id, std::queue<Instruction*>* insts) {
get_def_use_mgr()->ForEachUser(ptr_id, [this, insts](Instruction* user) {
SpvOp op = user->opcode();
if (IsNonPtrAccessChain(op)) {
AddStores(user->result_id(), insts);
} else if (op == SpvOpStore) {
insts->push(user);
}
});
}
void MemPass::DCEInst(Instruction* inst,
const std::function<void(Instruction*)>& call_back) {
std::queue<Instruction*> deadInsts;
deadInsts.push(inst);
while (!deadInsts.empty()) {
Instruction* di = deadInsts.front();
// Don't delete labels
if (di->opcode() == SpvOpLabel) {
deadInsts.pop();
continue;
}
// Remember operands
std::set<uint32_t> ids;
di->ForEachInId([&ids](uint32_t* iid) { ids.insert(*iid); });
uint32_t varId = 0;
// Remember variable if dead load
if (di->opcode() == SpvOpLoad) (void)GetPtr(di, &varId);
if (call_back) {
call_back(di);
}
context()->KillInst(di);
// For all operands with no remaining uses, add their instruction
// to the dead instruction queue.
for (auto id : ids)
if (HasOnlyNamesAndDecorates(id)) {
Instruction* odi = get_def_use_mgr()->GetDef(id);
if (context()->IsCombinatorInstruction(odi)) deadInsts.push(odi);
}
// if a load was deleted and it was the variable's
// last load, add all its stores to dead queue
if (varId != 0 && !IsLiveVar(varId)) AddStores(varId, &deadInsts);
deadInsts.pop();
}
}
MemPass::MemPass() {}
bool MemPass::HasOnlySupportedRefs(uint32_t varId) {
return get_def_use_mgr()->WhileEachUser(varId, [this](Instruction* user) {
SpvOp op = user->opcode();
if (op != SpvOpStore && op != SpvOpLoad && op != SpvOpName &&
!IsNonTypeDecorate(op)) {
return false;
}
return true;
});
}
uint32_t MemPass::Type2Undef(uint32_t type_id) {
const auto uitr = type2undefs_.find(type_id);
if (uitr != type2undefs_.end()) return uitr->second;
const uint32_t undefId = TakeNextId();
if (undefId == 0) {
return 0;
}
std::unique_ptr<Instruction> undef_inst(
new Instruction(context(), SpvOpUndef, type_id, undefId, {}));
get_def_use_mgr()->AnalyzeInstDefUse(&*undef_inst);
get_module()->AddGlobalValue(std::move(undef_inst));
type2undefs_[type_id] = undefId;
return undefId;
}
bool MemPass::IsTargetVar(uint32_t varId) {
if (varId == 0) {
return false;
}
if (seen_non_target_vars_.find(varId) != seen_non_target_vars_.end())
return false;
if (seen_target_vars_.find(varId) != seen_target_vars_.end()) return true;
const Instruction* varInst = get_def_use_mgr()->GetDef(varId);
if (varInst->opcode() != SpvOpVariable) return false;
const uint32_t varTypeId = varInst->type_id();
const Instruction* varTypeInst = get_def_use_mgr()->GetDef(varTypeId);
if (varTypeInst->GetSingleWordInOperand(kTypePointerStorageClassInIdx) !=
SpvStorageClassFunction) {
seen_non_target_vars_.insert(varId);
return false;
}
const uint32_t varPteTypeId =
varTypeInst->GetSingleWordInOperand(kTypePointerTypeIdInIdx);
Instruction* varPteTypeInst = get_def_use_mgr()->GetDef(varPteTypeId);
if (!IsTargetType(varPteTypeInst)) {
seen_non_target_vars_.insert(varId);
return false;
}
seen_target_vars_.insert(varId);
return true;
}
// Remove all |phi| operands coming from unreachable blocks (i.e., blocks not in
// |reachable_blocks|). There are two types of removal that this function can
// perform:
//
// 1- Any operand that comes directly from an unreachable block is completely
// removed. Since the block is unreachable, the edge between the unreachable
// block and the block holding |phi| has been removed.
//
// 2- Any operand that comes via a live block and was defined at an unreachable
// block gets its value replaced with an OpUndef value. Since the argument
// was generated in an unreachable block, it no longer exists, so it cannot
// be referenced. However, since the value does not reach |phi| directly
// from the unreachable block, the operand cannot be removed from |phi|.
// Therefore, we replace the argument value with OpUndef.
//
// For example, in the switch() below, assume that we want to remove the
// argument with value %11 coming from block %41.
//
// [ ... ]
// %41 = OpLabel <--- Unreachable block
// %11 = OpLoad %int %y
// [ ... ]
// OpSelectionMerge %16 None
// OpSwitch %12 %16 10 %13 13 %14 18 %15
// %13 = OpLabel
// OpBranch %16
// %14 = OpLabel
// OpStore %outparm %int_14
// OpBranch %16
// %15 = OpLabel
// OpStore %outparm %int_15
// OpBranch %16
// %16 = OpLabel
// %30 = OpPhi %int %11 %41 %int_42 %13 %11 %14 %11 %15
//
// Since %41 is now an unreachable block, the first operand of |phi| needs to
// be removed completely. But the operands (%11 %14) and (%11 %15) cannot be
// removed because %14 and %15 are reachable blocks. Since %11 no longer exist,
// in those arguments, we replace all references to %11 with an OpUndef value.
// This results in |phi| looking like:
//
// %50 = OpUndef %int
// [ ... ]
// %30 = OpPhi %int %int_42 %13 %50 %14 %50 %15
void MemPass::RemovePhiOperands(
Instruction* phi, const std::unordered_set<BasicBlock*>& reachable_blocks) {
std::vector<Operand> keep_operands;
uint32_t type_id = 0;
// The id of an undefined value we've generated.
uint32_t undef_id = 0;
// Traverse all the operands in |phi|. Build the new operand vector by adding
// all the original operands from |phi| except the unwanted ones.
for (uint32_t i = 0; i < phi->NumOperands();) {
if (i < 2) {
// The first two arguments are always preserved.
keep_operands.push_back(phi->GetOperand(i));
++i;
continue;
}
// The remaining Phi arguments come in pairs. Index 'i' contains the
// variable id, index 'i + 1' is the originating block id.
assert(i % 2 == 0 && i < phi->NumOperands() - 1 &&
"malformed Phi arguments");
BasicBlock* in_block = cfg()->block(phi->GetSingleWordOperand(i + 1));
if (reachable_blocks.find(in_block) == reachable_blocks.end()) {
// If the incoming block is unreachable, remove both operands as this
// means that the |phi| has lost an incoming edge.
i += 2;
continue;
}
// In all other cases, the operand must be kept but may need to be changed.
uint32_t arg_id = phi->GetSingleWordOperand(i);
Instruction* arg_def_instr = get_def_use_mgr()->GetDef(arg_id);
BasicBlock* def_block = context()->get_instr_block(arg_def_instr);
if (def_block &&
reachable_blocks.find(def_block) == reachable_blocks.end()) {
// If the current |phi| argument was defined in an unreachable block, it
// means that this |phi| argument is no longer defined. Replace it with
// |undef_id|.
if (!undef_id) {
type_id = arg_def_instr->type_id();
undef_id = Type2Undef(type_id);
}
keep_operands.push_back(
Operand(spv_operand_type_t::SPV_OPERAND_TYPE_ID, {undef_id}));
} else {
// Otherwise, the argument comes from a reachable block or from no block
// at all (meaning that it was defined in the global section of the
// program). In both cases, keep the argument intact.
keep_operands.push_back(phi->GetOperand(i));
}
keep_operands.push_back(phi->GetOperand(i + 1));
i += 2;
}
context()->ForgetUses(phi);
phi->ReplaceOperands(keep_operands);
context()->AnalyzeUses(phi);
}
void MemPass::RemoveBlock(Function::iterator* bi) {
auto& rm_block = **bi;
// Remove instructions from the block.
rm_block.ForEachInst([&rm_block, this](Instruction* inst) {
// Note that we do not kill the block label instruction here. The label
// instruction is needed to identify the block, which is needed by the
// removal of phi operands.
if (inst != rm_block.GetLabelInst()) {
context()->KillInst(inst);
}
});
// Remove the label instruction last.
auto label = rm_block.GetLabelInst();
context()->KillInst(label);
*bi = bi->Erase();
}
bool MemPass::RemoveUnreachableBlocks(Function* func) {
bool modified = false;
// Mark reachable all blocks reachable from the function's entry block.
std::unordered_set<BasicBlock*> reachable_blocks;
std::unordered_set<BasicBlock*> visited_blocks;
std::queue<BasicBlock*> worklist;
reachable_blocks.insert(func->entry().get());
// Initially mark the function entry point as reachable.
worklist.push(func->entry().get());
auto mark_reachable = [&reachable_blocks, &visited_blocks, &worklist,
this](uint32_t label_id) {
auto successor = cfg()->block(label_id);
if (visited_blocks.count(successor) == 0) {
reachable_blocks.insert(successor);
worklist.push(successor);
visited_blocks.insert(successor);
}
};
// Transitively mark all blocks reachable from the entry as reachable.
while (!worklist.empty()) {
BasicBlock* block = worklist.front();
worklist.pop();
// All the successors of a live block are also live.
static_cast<const BasicBlock*>(block)->ForEachSuccessorLabel(
mark_reachable);
// All the Merge and ContinueTarget blocks of a live block are also live.
block->ForMergeAndContinueLabel(mark_reachable);
}
// Update operands of Phi nodes that reference unreachable blocks.
for (auto& block : *func) {
// If the block is about to be removed, don't bother updating its
// Phi instructions.
if (reachable_blocks.count(&block) == 0) {
continue;
}
// If the block is reachable and has Phi instructions, remove all
// operands from its Phi instructions that reference unreachable blocks.
// If the block has no Phi instructions, this is a no-op.
block.ForEachPhiInst([&reachable_blocks, this](Instruction* phi) {
RemovePhiOperands(phi, reachable_blocks);
});
}
// Erase unreachable blocks.
for (auto ebi = func->begin(); ebi != func->end();) {
if (reachable_blocks.count(&*ebi) == 0) {
RemoveBlock(&ebi);
modified = true;
} else {
++ebi;
}
}
return modified;
}
bool MemPass::CFGCleanup(Function* func) {
bool modified = false;
modified |= RemoveUnreachableBlocks(func);
return modified;
}
void MemPass::CollectTargetVars(Function* func) {
seen_target_vars_.clear();
seen_non_target_vars_.clear();
type2undefs_.clear();
// Collect target (and non-) variable sets. Remove variables with
// non-load/store refs from target variable set
for (auto& blk : *func) {
for (auto& inst : blk) {
switch (inst.opcode()) {
case SpvOpStore:
case SpvOpLoad: {
uint32_t varId;
(void)GetPtr(&inst, &varId);
if (!IsTargetVar(varId)) break;
if (HasOnlySupportedRefs(varId)) break;
seen_non_target_vars_.insert(varId);
seen_target_vars_.erase(varId);
} break;
default:
break;
}
}
}
}
} // namespace opt
} // namespace spvtools