| // Copyright 2022 The Tint Authors. |
| // |
| // 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 "src/tint/transform/promote_initializers_to_let.h" |
| |
| #include <utility> |
| |
| #include "src/tint/ast/traverse_expressions.h" |
| #include "src/tint/program_builder.h" |
| #include "src/tint/sem/call.h" |
| #include "src/tint/sem/statement.h" |
| #include "src/tint/sem/value_constructor.h" |
| #include "src/tint/transform/utils/hoist_to_decl_before.h" |
| #include "src/tint/type/struct.h" |
| #include "src/tint/utils/hashset.h" |
| |
| TINT_INSTANTIATE_TYPEINFO(tint::transform::PromoteInitializersToLet); |
| |
| namespace tint::transform { |
| |
| PromoteInitializersToLet::PromoteInitializersToLet() = default; |
| |
| PromoteInitializersToLet::~PromoteInitializersToLet() = default; |
| |
| Transform::ApplyResult PromoteInitializersToLet::Apply(const Program* src, |
| const DataMap&, |
| DataMap&) const { |
| ProgramBuilder b; |
| CloneContext ctx{&b, src, /* auto_clone_symbols */ true}; |
| |
| // Returns true if the expression should be hoisted to a new let statement before the |
| // expression's statement. |
| auto should_hoist = [&](const sem::ValueExpression* expr) { |
| if (!expr->Type()->IsAnyOf<type::Array, type::Struct>()) { |
| // We only care about array and struct initializers |
| return false; |
| } |
| |
| // Check whether the expression is an array or structure constructor |
| { |
| // Follow const-chains |
| auto* root_expr = expr; |
| if (expr->Stage() == sem::EvaluationStage::kConstant) { |
| if (expr->Type()->HoldsAbstract()) { |
| // Do not hoist expressions that are not materialized, as doing so would cause |
| // premature materialization. |
| return false; |
| } |
| while (auto* user = root_expr->UnwrapMaterialize()->As<sem::VariableUser>()) { |
| root_expr = user->Variable()->Initializer(); |
| } |
| } |
| |
| auto* ctor = root_expr->UnwrapMaterialize()->As<sem::Call>(); |
| if (!ctor || !ctor->Target()->Is<sem::ValueConstructor>()) { |
| // Root expression is not a value constructor. Not interested in this. |
| return false; |
| } |
| } |
| |
| if (auto* src_var_decl = expr->Stmt()->Declaration()->As<ast::VariableDeclStatement>()) { |
| if (src_var_decl->variable->initializer == expr->Declaration()) { |
| // This statement is just a variable declaration with the initializer as the |
| // initializer value. This is what we're attempting to transform to, and so |
| // ignore. |
| return false; |
| } |
| } |
| |
| return true; |
| }; |
| |
| // A list of expressions that should be hoisted. |
| utils::Vector<const sem::ValueExpression*, 32> to_hoist; |
| // A set of expressions that are constant, which _may_ need to be hoisted. |
| utils::Hashset<const ast::Expression*, 32> const_chains; |
| |
| // Walk the AST nodes. This order guarantees that leaf-expressions are visited first. |
| for (auto* node : src->ASTNodes().Objects()) { |
| if (auto* sem = src->Sem().GetVal(node)) { |
| auto* stmt = sem->Stmt(); |
| if (!stmt) { |
| // Expression is outside of a statement. This usually means the expression is part |
| // of a global (module-scope) constant declaration. These must be constexpr, and so |
| // cannot contain the type of expressions that must be sanitized. |
| continue; |
| } |
| |
| if (sem->Stage() == sem::EvaluationStage::kConstant) { |
| // Expression is constant. We only need to hoist expressions if they're the |
| // outermost constant expression in a chain. Remove the immediate child nodes of the |
| // expression from const_chains, and add this expression to the const_chains. As we |
| // visit leaf-expressions first, this means the content of const_chains only |
| // contains the outer-most constant expressions. |
| auto* expr = sem->Declaration(); |
| bool ok = ast::TraverseExpressions( |
| expr, b.Diagnostics(), [&](const ast::Expression* child) { |
| const_chains.Remove(child); |
| return child == expr ? ast::TraverseAction::Descend |
| : ast::TraverseAction::Skip; |
| }); |
| if (!ok) { |
| return Program(std::move(b)); |
| } |
| const_chains.Add(expr); |
| } else if (should_hoist(sem)) { |
| to_hoist.Push(sem); |
| } |
| } |
| } |
| |
| // After walking the full AST, const_chains only contains the outer-most constant expressions. |
| // Check if any of these need hoisting, and append those to to_hoist. |
| for (auto* expr : const_chains) { |
| if (auto* sem = src->Sem().GetVal(expr); should_hoist(sem)) { |
| to_hoist.Push(sem); |
| } |
| } |
| |
| if (to_hoist.IsEmpty()) { |
| // Nothing to do. Skip. |
| return SkipTransform; |
| } |
| |
| // The order of to_hoist is currently undefined. Sort by AST node id, which will make this |
| // deterministic. |
| to_hoist.Sort([&](auto* expr_a, auto* expr_b) { |
| return expr_a->Declaration()->node_id < expr_b->Declaration()->node_id; |
| }); |
| |
| // Hoist all the expressions in to_hoist to a constant variable, declared just before the |
| // statement of usage. |
| HoistToDeclBefore hoist_to_decl_before(ctx); |
| for (auto* expr : to_hoist) { |
| if (!hoist_to_decl_before.Add(expr, expr->Declaration(), |
| HoistToDeclBefore::VariableKind::kLet)) { |
| return Program(std::move(b)); |
| } |
| } |
| |
| ctx.Clone(); |
| return Program(std::move(b)); |
| } |
| |
| } // namespace tint::transform |