slyubomirsky commented on code in PR #16117: URL: https://github.com/apache/tvm/pull/16117#discussion_r1393432650
########## src/relax/transform/remove_unused_outputs.cc: ########## @@ -0,0 +1,326 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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 <tvm/relax/analysis.h> +#include <tvm/relax/expr_functor.h> +#include <tvm/relax/transform.h> +#include <tvm/relax/utils.h> + +#include <algorithm> +#include <optional> +#include <tuple> + +namespace tvm { +namespace relax { + +namespace { + +template <typename T> +using PSet = std::unordered_set<T, ObjectPtrHash, ObjectPtrEqual>; + +template <typename T, typename U> +using PMap = std::unordered_map<T, U, ObjectPtrHash, ObjectPtrEqual>; + +class PartialTupleUsageCollector : ExprVisitor { + public: + static PMap<GlobalVar, std::vector<bool>> Collect(const IRModule& mod) { + PMap<GlobalVar, size_t> num_outputs; + + for (const auto& [gvar, base_func] : mod->functions) { + bool is_exposed = base_func->attrs.GetAttr<String>(tvm::attr::kGlobalSymbol).defined(); + + if (!is_exposed) { + if (auto relax_func = base_func.as<FunctionNode>()) { + if (auto out_tuple = relax_func->ret_struct_info.as<TupleStructInfoNode>()) { + num_outputs[gvar] = out_tuple->fields.size(); + } + } + } + } + + if (num_outputs.empty()) { + // Early bail-out if the module has no private functions that + // return tuples. + return {}; + } + + PartialTupleUsageCollector visitor(std::move(num_outputs)); + for (const auto& [gvar, base_func] : mod->functions) { + if (auto func = base_func.as<Function>()) { + visitor.VisitExpr(func.value()); + } + } + + PMap<GlobalVar, std::vector<bool>> to_update; + for (const auto& [gvar, mask] : visitor.output_usage_mask_) { + bool has_unused_output = + std::any_of(mask.begin(), mask.end(), [](const bool is_used) { return !is_used; }); + if (has_unused_output) { + to_update[gvar] = mask; + } + } + + return to_update; + } + + private: + PartialTupleUsageCollector(PMap<GlobalVar, size_t> num_outputs) { + for (const auto& [gvar, num_output] : num_outputs) { + output_usage_mask_[gvar] = std::vector<bool>(num_output, false); + } + } + + void VisitBinding(const Binding& binding) override { + ExprVisitor::VisitBinding(binding); + known_bindings_.Set(binding->var, GetBoundValue(binding)); + } + + void VisitExpr_(const TupleGetItemNode* op) override { + Expr tuple = UnwrapBindings(op->tuple); + + if (auto call = tuple.as<CallNode>()) { + if (auto opt_callee = call->op.as<GlobalVar>()) { + auto callee = opt_callee.value(); + if (auto it = output_usage_mask_.find(callee); it != output_usage_mask_.end()) { + auto& used_indices = it->second; + + CHECK_GE(op->index, 0) << "IndexError: " + << "Indices for TupleGetItem must be non-negative, " + << "but expression " << GetRef<Expr>(op) + << " uses a tuple index of " << op->index; + size_t index = op->index; + + CHECK_LT(index, used_indices.size()) + << "IndexError: " + << "Indices for TupleGetItem must be less than the size of the tuple, " + << "but expression " << GetRef<Expr>(op) << " uses a tuple index of " << op->index + << " for a tuple of size " << used_indices.size(); + used_indices[index] = true; + } + } + } + } + + Expr UnwrapBindings(Expr expr) const { + auto get_bound_value = [&](const Expr& expr) -> Optional<Expr> { + if (auto var = expr.as<Var>()) { + if (auto known_binding = known_bindings_.Get(var.value())) { + return known_binding.value(); + } + } + return NullOpt; + }; + + while (auto unwrapped = get_bound_value(expr)) { + expr = unwrapped.value(); + } + return expr; + } + + Map<Var, Expr> known_bindings_; + PMap<GlobalVar, std::vector<bool>> output_usage_mask_; +}; + +Function UpdateCallee(Function func, const std::vector<bool>& usage_mask) { + auto old_func_sinfo = func->struct_info_.as<FuncStructInfoNode>(); + + auto old_ret_sinfo = func->ret_struct_info.as<TupleStructInfoNode>(); + ICHECK(old_ret_sinfo) << "All functions returning non-tuple outputs " + << "should have been pruned already by PartialTupleUsageCollector"; + + Array<Expr> outputs; + + // This helper variable will be removed by the post-proc of + // CanonicalizeBindings and DeadCodeElimination. + Var previous_outputs("previous_outputs", func->ret_struct_info); + + for (size_t i = 0; i < usage_mask.size(); i++) { + if (usage_mask[i]) { + outputs.push_back(TupleGetItem(previous_outputs, i)); + } + } + + Expr new_output = outputs.size() == 1 ? outputs[0] : Tuple(outputs); + StructInfo new_return_sinfo = + outputs.size() == 1 ? GetStructInfo(outputs[0]) : TupleStructInfo(outputs.Map(GetStructInfo)); + + VarBinding binding(previous_outputs, func->body); + BindingBlock binding_block({binding}); + SeqExpr new_body({binding_block}, new_output); + + auto old_sinfo = Downcast<FuncStructInfo>(func->struct_info_); + FuncStructInfo new_sinfo(old_func_sinfo->params.value(), new_return_sinfo, + old_func_sinfo->purity); + + auto write_ptr = func.CopyOnWrite(); + write_ptr->struct_info_ = new_sinfo; + write_ptr->body = new_body; + + return func; +} + +class CallSiteMutator : public ExprMutator { + public: + CallSiteMutator(PMap<GlobalVar, std::function<Expr(Call)>> callsite_updaters) + : callsite_updaters_(callsite_updaters) {} + + using ExprMutator::VisitExpr_; + + Expr VisitExpr_(const CallNode* op) override { + auto node = Downcast<Call>(ExprMutator::VisitExpr_(op)); + + if (auto gvar = node->op.as<GlobalVar>()) { + if (auto it = callsite_updaters_.find(gvar.value()); it != callsite_updaters_.end()) { + return it->second(node); + } + } + + return node; + } + + PMap<GlobalVar, std::function<Expr(Call)>> callsite_updaters_; +}; + +} // namespace + +namespace transform { + +Pass RemoveUnusedOutputs() { + runtime::TypedPackedFunc<IRModule(IRModule, PassContext)> pass_func = + [=](IRModule mod, PassContext pc) -> IRModule { + auto usage = PartialTupleUsageCollector::Collect(mod); + + if (usage.empty()) { + // Early bail-out if there are no updates to make. + return mod; + } + + PMap<GlobalVar, std::function<Expr(Call)>> callsite_updaters; + + { + IRModule new_callees; + + for (const auto& [gvar, base_func] : mod->functions) { + if (auto func = base_func.as<Function>()) { + if (auto it = usage.find(gvar); it != usage.end()) { + const auto& usage_mask = it->second; + auto new_func = UpdateCallee(func.value(), usage_mask); + + GlobalVar new_gvar(gvar->name_hint, new_func->checked_type_); + new_gvar->struct_info_ = new_func->struct_info_; + new_callees->Add(new_gvar, new_func); + + callsite_updaters[gvar] = [old_gvar = gvar, new_gvar, usage_mask](Call call) -> Expr { + ICHECK(call->op.same_as(old_gvar)) << "InternalError: " + << "Updater should be applied to " << old_gvar + << ", but was applied to " << call->op; + + auto old_call_sinfo = call->struct_info_.as<TupleStructInfoNode>(); + ICHECK(old_call_sinfo) + << "InternalError: " + << "Updater should be applied to Call producing an output tuple, " + << "but " << call << " has struct info " << call->struct_info_; + CHECK_EQ(usage_mask.size(), old_call_sinfo->fields.size()) + << "Function " << call->op << " produces " << usage_mask.size() << " outputs, " + << "but " << call << " was used in a context expecting " + << old_call_sinfo->fields.size() << " outputs."; + + Call new_call(new_gvar, call->args); + + int num_outputs_used = 0; + for (bool used : usage_mask) { + num_outputs_used += used; Review Comment: I'm surprised you don't get a warning for this cast. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
