void DeadVariableElimination::DeleteVariable(uint32_t result_id) {
ir::Instruction* inst = get_def_use_mgr()->GetDef(result_id);
assert(inst->opcode() == SpvOpVariable &&
"Should not be trying to delete anything other than an OpVariable.");
// Look for an initializer that references another variable. We need to know
// if that variable can be deleted after the reference is removed.
if (inst->NumOperands() == 4) {
ir::Instruction* initializer =
get_def_use_mgr()->GetDef(inst->GetSingleWordOperand(3));
// TODO: Handle OpSpecConstantOP which might be defined in terms of other
// variables. Will probably require a unified dead code pass that does all
// instruction types. (Issue 906)
if (initializer->opcode() == SpvOpVariable) {
uint32_t initializer_id = initializer->result_id();
size_t& count = reference_count_[initializer_id];
if (count != kMustKeep) {
--count;
}
if (count == 0) {
DeleteVariable(initializer_id);
}
}
}
context()->KillDef(result_id);
}
bool AggressiveDCEPass::IsVarOfStorage(uint32_t varId, uint32_t storageClass) {
if (varId == 0) return false;
const Instruction* varInst = get_def_use_mgr()->GetDef(varId);
const SpvOp op = varInst->opcode();
if (op != SpvOpVariable) return false;
const uint32_t varTypeId = varInst->type_id();
const Instruction* varTypeInst = get_def_use_mgr()->GetDef(varTypeId);
if (varTypeInst->opcode() != SpvOpTypePointer) return false;
return varTypeInst->GetSingleWordInOperand(kTypePointerStorageClassInIdx) ==
storageClass;
}
// This optimization removes global variables that are not needed because they
// are definitely not accessed.
Pass::Status DeadVariableElimination::Process(ir::IRContext* c) {
// The algorithm will compute the reference count for every global variable.
// Anything with a reference count of 0 will then be deleted. For variables
// that might have references that are not explicit in this context, we use
// the
// value kMustKeep as the reference count.
InitializeProcessing(c);
std::vector<uint32_t> ids_to_remove;
// Get the reference count for all of the global OpVariable instructions.
for (auto& inst : context()->types_values()) {
if (inst.opcode() != SpvOp::SpvOpVariable) {
continue;
}
size_t count = 0;
uint32_t result_id = inst.result_id();
// Check the linkage. If it is exported, it could be reference somewhere
// else, so we must keep the variable around.
get_decoration_mgr()->ForEachDecoration(
result_id, SpvDecorationLinkageAttributes,
[&count](const ir::Instruction& linkage_instruction) {
uint32_t last_operand = linkage_instruction.NumOperands() - 1;
if (linkage_instruction.GetSingleWordOperand(last_operand) ==
SpvLinkageTypeExport) {
count = kMustKeep;
}
});
if (count != kMustKeep) {
// If we don't have to keep the instruction for other reasons, then look
// at the uses and count the number of real references.
count = 0;
get_def_use_mgr()->ForEachUser(
result_id, [&count](ir::Instruction* user) {
if (!ir::IsAnnotationInst(user->opcode()) &&
user->opcode() != SpvOpName) {
++count;
}
});
}
reference_count_[result_id] = count;
if (count == 0) {
ids_to_remove.push_back(result_id);
}
}
// Remove all of the variables that have a reference count of 0.
bool modified = false;
if (!ids_to_remove.empty()) {
modified = true;
for (auto result_id : ids_to_remove) {
DeleteVariable(result_id);
}
}
return (modified ? Status::SuccessWithChange : Status::SuccessWithoutChange);
}
void LocalAccessChainConvertPass::BuildAndAppendInst(
SpvOp opcode, uint32_t typeId, uint32_t resultId,
const std::vector<Operand>& in_opnds,
std::vector<std::unique_ptr<Instruction>>* newInsts) {
std::unique_ptr<Instruction> newInst(
new Instruction(context(), opcode, typeId, resultId, in_opnds));
get_def_use_mgr()->AnalyzeInstDefUse(&*newInst);
newInsts->emplace_back(std::move(newInst));
}
bool AggressiveDCEPass::IsTargetDead(Instruction* inst) {
const uint32_t tId = inst->GetSingleWordInOperand(0);
Instruction* tInst = get_def_use_mgr()->GetDef(tId);
if (IsAnnotationInst(tInst->opcode())) {
// This must be a decoration group. We go through annotations in a specific
// order. So if this is not used by any group or group member decorates, it
// is dead.
assert(tInst->opcode() == SpvOpDecorationGroup);
bool dead = true;
get_def_use_mgr()->ForEachUser(tInst, [&dead](Instruction* user) {
if (user->opcode() == SpvOpGroupDecorate ||
user->opcode() == SpvOpGroupMemberDecorate)
dead = false;
});
return dead;
}
return IsDead(tInst);
}
bool BlockMergePass::IsMerge(uint32_t id) {
return !get_def_use_mgr()->WhileEachUse(id, [](Instruction* user,
uint32_t index) {
SpvOp op = user->opcode();
if ((op == SpvOpLoopMerge || op == SpvOpSelectionMerge) && index == 0u) {
return false;
}
return true;
});
}
bool LocalAccessChainConvertPass::IsConstantIndexAccessChain(
const Instruction* acp) const {
uint32_t inIdx = 0;
return acp->WhileEachInId([&inIdx, this](const uint32_t* tid) {
if (inIdx > 0) {
Instruction* opInst = get_def_use_mgr()->GetDef(*tid);
if (opInst->opcode() != SpvOpConstant) return false;
}
++inIdx;
return true;
});
}
void LocalAccessChainConvertPass::AppendConstantOperands(
const Instruction* ptrInst, std::vector<Operand>* in_opnds) {
uint32_t iidIdx = 0;
ptrInst->ForEachInId([&iidIdx, &in_opnds, this](const uint32_t* iid) {
if (iidIdx > 0) {
const Instruction* cInst = get_def_use_mgr()->GetDef(*iid);
uint32_t val = cInst->GetSingleWordInOperand(kConstantValueInIdx);
in_opnds->push_back(
{spv_operand_type_t::SPV_OPERAND_TYPE_LITERAL_INTEGER, {val}});
}
++iidIdx;
});
}
uint32_t LocalAccessChainConvertPass::BuildAndAppendVarLoad(
const Instruction* ptrInst, uint32_t* varId, uint32_t* varPteTypeId,
std::vector<std::unique_ptr<Instruction>>* newInsts) {
const uint32_t ldResultId = TakeNextId();
*varId = ptrInst->GetSingleWordInOperand(kAccessChainPtrIdInIdx);
const Instruction* varInst = get_def_use_mgr()->GetDef(*varId);
assert(varInst->opcode() == SpvOpVariable);
*varPteTypeId = GetPointeeTypeId(varInst);
BuildAndAppendInst(SpvOpLoad, *varPteTypeId, ldResultId,
{{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {*varId}}},
newInsts);
return ldResultId;
}
bool LocalSingleBlockLoadStoreElimPass::HasOnlySupportedRefs(uint32_t ptrId) {
if (supported_ref_ptrs_.find(ptrId) != supported_ref_ptrs_.end()) return true;
if (get_def_use_mgr()->WhileEachUser(ptrId, [this](Instruction* user) {
SpvOp op = user->opcode();
if (IsNonPtrAccessChain(op) || op == SpvOpCopyObject) {
if (!HasOnlySupportedRefs(user->result_id())) {
return false;
}
} else if (op != SpvOpStore && op != SpvOpLoad && op != SpvOpName &&
!IsNonTypeDecorate(op)) {
return false;
}
return true;
})) {
supported_ref_ptrs_.insert(ptrId);
return true;
}
return false;
}
void AggressiveDCEPass::AddStores(uint32_t ptrId) {
get_def_use_mgr()->ForEachUser(ptrId, [this, ptrId](Instruction* user) {
switch (user->opcode()) {
case SpvOpAccessChain:
case SpvOpInBoundsAccessChain:
case SpvOpCopyObject:
this->AddStores(user->result_id());
break;
case SpvOpLoad:
break;
case SpvOpCopyMemory:
case SpvOpCopyMemorySized:
if (user->GetSingleWordInOperand(kCopyMemoryTargetAddrInIdx) == ptrId) {
AddToWorklist(user);
}
break;
// If default, assume it stores e.g. frexp, modf, function call
case SpvOpStore:
default:
AddToWorklist(user);
break;
}
});
}
bool AggressiveDCEPass::ProcessGlobalValues() {
// Remove debug and annotation statements referencing dead instructions.
// This must be done before killing the instructions, otherwise there are
// dead objects in the def/use database.
bool modified = false;
Instruction* instruction = &*get_module()->debug2_begin();
while (instruction) {
if (instruction->opcode() != SpvOpName) {
instruction = instruction->NextNode();
continue;
}
if (IsTargetDead(instruction)) {
instruction = context()->KillInst(instruction);
modified = true;
} else {
instruction = instruction->NextNode();
}
}
// This code removes all unnecessary decorations safely (see #1174). It also
// does so in a more efficient manner than deleting them only as the targets
// are deleted.
std::vector<Instruction*> annotations;
for (auto& inst : get_module()->annotations()) annotations.push_back(&inst);
std::sort(annotations.begin(), annotations.end(), DecorationLess());
for (auto annotation : annotations) {
switch (annotation->opcode()) {
case SpvOpDecorate:
case SpvOpMemberDecorate:
case SpvOpDecorateStringGOOGLE:
case SpvOpMemberDecorateStringGOOGLE:
if (IsTargetDead(annotation)) {
context()->KillInst(annotation);
modified = true;
}
break;
case SpvOpDecorateId:
if (IsTargetDead(annotation)) {
context()->KillInst(annotation);
modified = true;
} else {
if (annotation->GetSingleWordInOperand(1) ==
SpvDecorationHlslCounterBufferGOOGLE) {
// HlslCounterBuffer will reference an id other than the target.
// If that id is dead, then the decoration can be removed as well.
uint32_t counter_buffer_id = annotation->GetSingleWordInOperand(2);
Instruction* counter_buffer_inst =
get_def_use_mgr()->GetDef(counter_buffer_id);
if (IsDead(counter_buffer_inst)) {
context()->KillInst(annotation);
modified = true;
}
}
}
break;
case SpvOpGroupDecorate: {
// Go through the targets of this group decorate. Remove each dead
// target. If all targets are dead, remove this decoration.
bool dead = true;
bool removed_operand = false;
for (uint32_t i = 1; i < annotation->NumOperands();) {
Instruction* opInst =
get_def_use_mgr()->GetDef(annotation->GetSingleWordOperand(i));
if (IsDead(opInst)) {
// Don't increment |i|.
annotation->RemoveOperand(i);
modified = true;
removed_operand = true;
} else {
i++;
dead = false;
}
}
if (dead) {
context()->KillInst(annotation);
modified = true;
} else if (removed_operand) {
context()->UpdateDefUse(annotation);
}
break;
}
case SpvOpGroupMemberDecorate: {
// Go through the targets of this group member decorate. Remove each
// dead target (and member index). If all targets are dead, remove this
// decoration.
bool dead = true;
bool removed_operand = false;
for (uint32_t i = 1; i < annotation->NumOperands();) {
Instruction* opInst =
get_def_use_mgr()->GetDef(annotation->GetSingleWordOperand(i));
if (IsDead(opInst)) {
// Don't increment |i|.
annotation->RemoveOperand(i + 1);
annotation->RemoveOperand(i);
modified = true;
removed_operand = true;
} else {
i += 2;
dead = false;
}
}
if (dead) {
context()->KillInst(annotation);
modified = true;
} else if (removed_operand) {
context()->UpdateDefUse(annotation);
}
break;
}
case SpvOpDecorationGroup:
// By the time we hit decoration groups we've checked everything that
// can target them. So if they have no uses they must be dead.
if (get_def_use_mgr()->NumUsers(annotation) == 0) {
context()->KillInst(annotation);
modified = true;
}
break;
default:
assert(false);
break;
}
}
// Since ADCE is disabled for non-shaders, we don't check for export linkage
// attributes here.
for (auto& val : get_module()->types_values()) {
if (IsDead(&val)) {
to_kill_.push_back(&val);
}
}
return modified;
}
bool AggressiveDCEPass::AggressiveDCE(Function* func) {
// Mark function parameters as live.
AddToWorklist(&func->DefInst());
func->ForEachParam(
[this](const Instruction* param) {
AddToWorklist(const_cast<Instruction*>(param));
},
false);
// Compute map from block to controlling conditional branch
std::list<BasicBlock*> structuredOrder;
cfg()->ComputeStructuredOrder(func, &*func->begin(), &structuredOrder);
ComputeBlock2HeaderMaps(structuredOrder);
bool modified = false;
// Add instructions with external side effects to worklist. Also add branches
// EXCEPT those immediately contained in an "if" selection construct or a loop
// or continue construct.
// TODO(greg-lunarg): Handle Frexp, Modf more optimally
call_in_func_ = false;
func_is_entry_point_ = false;
private_stores_.clear();
// Stacks to keep track of when we are inside an if- or loop-construct.
// When immediately inside an if- or loop-construct, we do not initially
// mark branches live. All other branches must be marked live.
std::stack<bool> assume_branches_live;
std::stack<uint32_t> currentMergeBlockId;
// Push sentinel values on stack for when outside of any control flow.
assume_branches_live.push(true);
currentMergeBlockId.push(0);
for (auto bi = structuredOrder.begin(); bi != structuredOrder.end(); ++bi) {
// If exiting if or loop, update stacks
if ((*bi)->id() == currentMergeBlockId.top()) {
assume_branches_live.pop();
currentMergeBlockId.pop();
}
for (auto ii = (*bi)->begin(); ii != (*bi)->end(); ++ii) {
SpvOp op = ii->opcode();
switch (op) {
case SpvOpStore: {
uint32_t varId;
(void)GetPtr(&*ii, &varId);
// Mark stores as live if their variable is not function scope
// and is not private scope. Remember private stores for possible
// later inclusion. We cannot call IsLocalVar at this point because
// private_like_local_ has not been set yet.
if (IsVarOfStorage(varId, SpvStorageClassPrivate) ||
IsVarOfStorage(varId, SpvStorageClassWorkgroup))
private_stores_.push_back(&*ii);
else if (!IsVarOfStorage(varId, SpvStorageClassFunction))
AddToWorklist(&*ii);
} break;
case SpvOpCopyMemory:
case SpvOpCopyMemorySized: {
uint32_t varId;
(void)GetPtr(ii->GetSingleWordInOperand(kCopyMemoryTargetAddrInIdx),
&varId);
if (IsVarOfStorage(varId, SpvStorageClassPrivate) ||
IsVarOfStorage(varId, SpvStorageClassWorkgroup))
private_stores_.push_back(&*ii);
else if (!IsVarOfStorage(varId, SpvStorageClassFunction))
AddToWorklist(&*ii);
} break;
case SpvOpLoopMerge: {
assume_branches_live.push(false);
currentMergeBlockId.push(
ii->GetSingleWordInOperand(kLoopMergeMergeBlockIdInIdx));
} break;
case SpvOpSelectionMerge: {
assume_branches_live.push(false);
currentMergeBlockId.push(
ii->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx));
} break;
case SpvOpSwitch:
case SpvOpBranch:
case SpvOpBranchConditional:
case SpvOpUnreachable: {
if (assume_branches_live.top()) {
AddToWorklist(&*ii);
}
} break;
default: {
// Function calls, atomics, function params, function returns, etc.
// TODO(greg-lunarg): function calls live only if write to non-local
if (!ii->IsOpcodeSafeToDelete()) {
AddToWorklist(&*ii);
}
// Remember function calls
if (op == SpvOpFunctionCall) call_in_func_ = true;
} break;
}
}
}
// See if current function is an entry point
for (auto& ei : get_module()->entry_points()) {
if (ei.GetSingleWordInOperand(kEntryPointFunctionIdInIdx) ==
func->result_id()) {
func_is_entry_point_ = true;
break;
}
}
// If the current function is an entry point and has no function calls,
// we can optimize private variables as locals
private_like_local_ = func_is_entry_point_ && !call_in_func_;
// If privates are not like local, add their stores to worklist
if (!private_like_local_)
for (auto& ps : private_stores_) AddToWorklist(ps);
// Perform closure on live instruction set.
while (!worklist_.empty()) {
Instruction* liveInst = worklist_.front();
// Add all operand instructions if not already live
liveInst->ForEachInId([&liveInst, this](const uint32_t* iid) {
Instruction* inInst = get_def_use_mgr()->GetDef(*iid);
// Do not add label if an operand of a branch. This is not needed
// as part of live code discovery and can create false live code,
// for example, the branch to a header of a loop.
if (inInst->opcode() == SpvOpLabel && liveInst->IsBranch()) return;
AddToWorklist(inInst);
});
if (liveInst->type_id() != 0) {
AddToWorklist(get_def_use_mgr()->GetDef(liveInst->type_id()));
}
// If in a structured if or loop construct, add the controlling
// conditional branch and its merge.
BasicBlock* blk = context()->get_instr_block(liveInst);
Instruction* branchInst = block2headerBranch_[blk];
if (branchInst != nullptr) {
AddToWorklist(branchInst);
Instruction* mergeInst = branch2merge_[branchInst];
AddToWorklist(mergeInst);
}
// If the block is a header, add the next outermost controlling
// conditional branch and its merge.
Instruction* nextBranchInst = header2nextHeaderBranch_[blk];
if (nextBranchInst != nullptr) {
AddToWorklist(nextBranchInst);
Instruction* mergeInst = branch2merge_[nextBranchInst];
AddToWorklist(mergeInst);
}
// If local load, add all variable's stores if variable not already live
if (liveInst->opcode() == SpvOpLoad || liveInst->IsAtomicWithLoad()) {
uint32_t varId;
(void)GetPtr(liveInst, &varId);
if (varId != 0) {
ProcessLoad(varId);
}
// Process memory copies like loads
} else if (liveInst->opcode() == SpvOpCopyMemory ||
liveInst->opcode() == SpvOpCopyMemorySized) {
uint32_t varId;
(void)GetPtr(liveInst->GetSingleWordInOperand(kCopyMemorySourceAddrInIdx),
&varId);
if (varId != 0) {
ProcessLoad(varId);
}
// If merge, add other branches that are part of its control structure
} else if (liveInst->opcode() == SpvOpLoopMerge ||
liveInst->opcode() == SpvOpSelectionMerge) {
AddBreaksAndContinuesToWorklist(liveInst);
// If function call, treat as if it loads from all pointer arguments
} else if (liveInst->opcode() == SpvOpFunctionCall) {
liveInst->ForEachInId([this](const uint32_t* iid) {
// Skip non-ptr args
if (!IsPtr(*iid)) return;
uint32_t varId;
(void)GetPtr(*iid, &varId);
ProcessLoad(varId);
});
// If function parameter, treat as if it's result id is loaded from
} else if (liveInst->opcode() == SpvOpFunctionParameter) {
ProcessLoad(liveInst->result_id());
// We treat an OpImageTexelPointer as a load of the pointer, and
// that value is manipulated to get the result.
} else if (liveInst->opcode() == SpvOpImageTexelPointer) {
uint32_t varId;
(void)GetPtr(liveInst, &varId);
if (varId != 0) {
ProcessLoad(varId);
}
}
worklist_.pop();
}
// Kill dead instructions and remember dead blocks
for (auto bi = structuredOrder.begin(); bi != structuredOrder.end();) {
uint32_t mergeBlockId = 0;
(*bi)->ForEachInst([this, &modified, &mergeBlockId](Instruction* inst) {
if (!IsDead(inst)) return;
if (inst->opcode() == SpvOpLabel) return;
// If dead instruction is selection merge, remember merge block
// for new branch at end of block
if (inst->opcode() == SpvOpSelectionMerge ||
inst->opcode() == SpvOpLoopMerge)
mergeBlockId = inst->GetSingleWordInOperand(0);
to_kill_.push_back(inst);
modified = true;
});
// If a structured if or loop was deleted, add a branch to its merge
// block, and traverse to the merge block and continue processing there.
// We know the block still exists because the label is not deleted.
if (mergeBlockId != 0) {
AddBranch(mergeBlockId, *bi);
for (++bi; (*bi)->id() != mergeBlockId; ++bi) {
}
auto merge_terminator = (*bi)->terminator();
if (merge_terminator->opcode() == SpvOpUnreachable) {
// The merge was unreachable. This is undefined behaviour so just
// return (or return an undef). Then mark the new return as live.
auto func_ret_type_inst = get_def_use_mgr()->GetDef(func->type_id());
if (func_ret_type_inst->opcode() == SpvOpTypeVoid) {
merge_terminator->SetOpcode(SpvOpReturn);
} else {
// Find an undef for the return value and make sure it gets kept by
// the pass.
auto undef_id = Type2Undef(func->type_id());
auto undef = get_def_use_mgr()->GetDef(undef_id);
live_insts_.Set(undef->unique_id());
merge_terminator->SetOpcode(SpvOpReturnValue);
merge_terminator->SetInOperands({{SPV_OPERAND_TYPE_ID, {undef_id}}});
get_def_use_mgr()->AnalyzeInstUse(merge_terminator);
}
live_insts_.Set(merge_terminator->unique_id());
}
} else {
++bi;
}
}
return modified;
}
void AggressiveDCEPass::AddBreaksAndContinuesToWorklist(
Instruction* mergeInst) {
assert(mergeInst->opcode() == SpvOpSelectionMerge ||
mergeInst->opcode() == SpvOpLoopMerge);
BasicBlock* header = context()->get_instr_block(mergeInst);
uint32_t headerIndex = structured_order_index_[header];
const uint32_t mergeId = mergeInst->GetSingleWordInOperand(0);
BasicBlock* merge = context()->get_instr_block(mergeId);
uint32_t mergeIndex = structured_order_index_[merge];
get_def_use_mgr()->ForEachUser(
mergeId, [headerIndex, mergeIndex, this](Instruction* user) {
if (!user->IsBranch()) return;
BasicBlock* block = context()->get_instr_block(user);
uint32_t index = structured_order_index_[block];
if (headerIndex < index && index < mergeIndex) {
// This is a break from the loop.
AddToWorklist(user);
// Add branch's merge if there is one.
Instruction* userMerge = branch2merge_[user];
if (userMerge != nullptr) AddToWorklist(userMerge);
}
});
if (mergeInst->opcode() != SpvOpLoopMerge) {
return;
}
// For loops we need to find the continues as well.
const uint32_t contId =
mergeInst->GetSingleWordInOperand(kLoopMergeContinueBlockIdInIdx);
get_def_use_mgr()->ForEachUser(contId, [&contId, this](Instruction* user) {
SpvOp op = user->opcode();
if (op == SpvOpBranchConditional || op == SpvOpSwitch) {
// A conditional branch or switch can only be a continue if it does not
// have a merge instruction or its merge block is not the continue block.
Instruction* hdrMerge = branch2merge_[user];
if (hdrMerge != nullptr && hdrMerge->opcode() == SpvOpSelectionMerge) {
uint32_t hdrMergeId =
hdrMerge->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx);
if (hdrMergeId == contId) return;
// Need to mark merge instruction too
AddToWorklist(hdrMerge);
}
} else if (op == SpvOpBranch) {
// An unconditional branch can only be a continue if it is not
// branching to its own merge block.
BasicBlock* blk = context()->get_instr_block(user);
Instruction* hdrBranch = block2headerBranch_[blk];
if (hdrBranch == nullptr) return;
Instruction* hdrMerge = branch2merge_[hdrBranch];
if (hdrMerge->opcode() == SpvOpLoopMerge) return;
uint32_t hdrMergeId =
hdrMerge->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx);
if (contId == hdrMergeId) return;
} else {
return;
}
AddToWorklist(user);
});
}
bool BlockMergePass::IsHeader(uint32_t id) {
return IsHeader(context()->get_instr_block(get_def_use_mgr()->GetDef(id)));
}
