bool LocalAccessChainConvertPass::HasOnlySupportedRefs(uint32_t ptrId) {
if (supported_ref_ptrs_.find(ptrId) != supported_ref_ptrs_.end())
return true;
analysis::UseList* uses = def_use_mgr_->GetUses(ptrId);
assert(uses != nullptr);
for (auto u : *uses) {
SpvOp op = u.inst->opcode();
if (IsNonPtrAccessChain(op) || op == SpvOpCopyObject) {
if (!HasOnlySupportedRefs(u.inst->result_id())) return false;
} else if (op != SpvOpStore && op != SpvOpLoad && op != SpvOpName &&
!IsNonTypeDecorate(op))
return false;
}
supported_ref_ptrs_.insert(ptrId);
return true;
}
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 LocalAccessChainConvertPass::FindTargetVars(ir::Function* func) {
for (auto bi = func->begin(); bi != func->end(); ++bi) {
for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
switch (ii->opcode()) {
case SpvOpStore:
case SpvOpLoad: {
uint32_t varId;
ir::Instruction* ptrInst = GetPtr(&*ii, &varId);
if (!IsTargetVar(varId))
break;
const SpvOp op = ptrInst->opcode();
// Rule out variables with non-supported refs eg function calls
if (!HasOnlySupportedRefs(varId)) {
seen_non_target_vars_.insert(varId);
seen_target_vars_.erase(varId);
break;
}
// Rule out variables with nested access chains
// TODO(): Convert nested access chains
if (IsNonPtrAccessChain(op) &&
ptrInst->GetSingleWordInOperand(kAccessChainPtrIdInIdx) != varId) {
seen_non_target_vars_.insert(varId);
seen_target_vars_.erase(varId);
break;
}
// Rule out variables accessed with non-constant indices
if (!IsConstantIndexAccessChain(ptrInst)) {
seen_non_target_vars_.insert(varId);
seen_target_vars_.erase(varId);
break;
}
} break;
default:
break;
}
}
}
}
bool LocalSingleBlockLoadStoreElimPass::LocalSingleBlockLoadStoreElim(
Function* func) {
// Perform local store/load, load/load and store/store elimination
// on each block
bool modified = false;
std::vector<Instruction*> instructions_to_kill;
std::unordered_set<Instruction*> instructions_to_save;
for (auto bi = func->begin(); bi != func->end(); ++bi) {
var2store_.clear();
var2load_.clear();
auto next = bi->begin();
for (auto ii = next; ii != bi->end(); ii = next) {
++next;
switch (ii->opcode()) {
case SpvOpStore: {
// Verify store variable is target type
uint32_t varId;
Instruction* ptrInst = GetPtr(&*ii, &varId);
if (!IsTargetVar(varId)) continue;
if (!HasOnlySupportedRefs(varId)) continue;
// If a store to the whole variable, remember it for succeeding
// loads and stores. Otherwise forget any previous store to that
// variable.
if (ptrInst->opcode() == SpvOpVariable) {
// If a previous store to same variable, mark the store
// for deletion if not still used.
auto prev_store = var2store_.find(varId);
if (prev_store != var2store_.end() &&
instructions_to_save.count(prev_store->second) == 0) {
instructions_to_kill.push_back(prev_store->second);
modified = true;
}
bool kill_store = false;
auto li = var2load_.find(varId);
if (li != var2load_.end()) {
if (ii->GetSingleWordInOperand(kStoreValIdInIdx) ==
li->second->result_id()) {
// We are storing the same value that already exists in the
// memory location. The store does nothing.
kill_store = true;
}
}
if (!kill_store) {
var2store_[varId] = &*ii;
var2load_.erase(varId);
} else {
instructions_to_kill.push_back(&*ii);
modified = true;
}
} else {
assert(IsNonPtrAccessChain(ptrInst->opcode()));
var2store_.erase(varId);
var2load_.erase(varId);
}
} break;
case SpvOpLoad: {
// Verify store variable is target type
uint32_t varId;
Instruction* ptrInst = GetPtr(&*ii, &varId);
if (!IsTargetVar(varId)) continue;
if (!HasOnlySupportedRefs(varId)) continue;
uint32_t replId = 0;
if (ptrInst->opcode() == SpvOpVariable) {
// If a load from a variable, look for a previous store or
// load from that variable and use its value.
auto si = var2store_.find(varId);
if (si != var2store_.end()) {
replId = si->second->GetSingleWordInOperand(kStoreValIdInIdx);
} else {
auto li = var2load_.find(varId);
if (li != var2load_.end()) {
replId = li->second->result_id();
}
}
} else {
// If a partial load of a previously seen store, remember
// not to delete the store.
auto si = var2store_.find(varId);
if (si != var2store_.end()) instructions_to_save.insert(si->second);
}
if (replId != 0) {
// replace load's result id and delete load
context()->KillNamesAndDecorates(&*ii);
context()->ReplaceAllUsesWith(ii->result_id(), replId);
instructions_to_kill.push_back(&*ii);
modified = true;
} else {
if (ptrInst->opcode() == SpvOpVariable)
var2load_[varId] = &*ii; // register load
}
} break;
case SpvOpFunctionCall: {
// Conservatively assume all locals are redefined for now.
// TODO(): Handle more optimally
var2store_.clear();
var2load_.clear();
} break;
default:
break;
}
}
}
for (Instruction* inst : instructions_to_kill) {
context()->KillInst(inst);
}
return modified;
}
