src/tint/transform/remove_continue_in_switch.cc

// 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/remove_continue_in_switch.h"

#include <string>
#include <unordered_map>
#include <utility>

#include "src/tint/ast/continue_statement.h"
#include "src/tint/ast/switch_statement.h"
#include "src/tint/program_builder.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/for_loop_statement.h"
#include "src/tint/sem/loop_statement.h"
#include "src/tint/sem/switch_statement.h"
#include "src/tint/transform/utils/get_insertion_point.h"
#include "src/tint/utils/map.h"

TINT_INSTANTIATE_TYPEINFO(tint::transform::RemoveContinueInSwitch);

namespace tint::transform {
namespace {

class State {
  private:
    CloneContext& ctx;
    ProgramBuilder& b;
    const sem::Info& sem;

    // Map of switch statement to 'tint_continue' variable.
    std::unordered_map<const ast::SwitchStatement*, Symbol> switch_to_cont_var_name;

    // If `cont` is within a switch statement within a loop, returns a pointer to
    // that switch statement.
    static const ast::SwitchStatement* GetParentSwitchInLoop(const sem::Info& sem,
                                                             const ast::ContinueStatement* cont) {
        // Find whether first parent is a switch or a loop
        auto* sem_stmt = sem.Get(cont);
        auto* sem_parent = sem_stmt->FindFirstParent<sem::SwitchStatement, sem::LoopBlockStatement,
                                                     sem::ForLoopStatement>();
        if (!sem_parent) {
            return nullptr;
        }
        return sem_parent->Declaration()->As<ast::SwitchStatement>();
    }

  public:
    /// Constructor
    /// @param ctx_in the context
    explicit State(CloneContext& ctx_in) : ctx(ctx_in), b(*ctx_in.dst), sem(ctx_in.src->Sem()) {}

    /// Returns true if this transform should be run for the given program
    static bool ShouldRun(const Program* program) {
        for (auto* node : program->ASTNodes().Objects()) {
            auto* stmt = node->As<ast::ContinueStatement>();
            if (!stmt) {
                continue;
            }
            if (GetParentSwitchInLoop(program->Sem(), stmt)) {
                return true;
            }
        }
        return false;
    }

    /// Runs the transform
    void Run() {
        for (auto* node : ctx.src->ASTNodes().Objects()) {
            auto* cont = node->As<ast::ContinueStatement>();
            if (!cont) {
                continue;
            }

            // If first parent is not a switch within a loop, skip
            auto* switch_stmt = GetParentSwitchInLoop(sem, cont);
            if (!switch_stmt) {
                continue;
            }

            auto cont_var_name =
                tint::utils::GetOrCreate(switch_to_cont_var_name, switch_stmt, [&]() {
                    // Create and insert 'var tint_continue : bool = false;' before the
                    // switch.
                    auto var_name = b.Symbols().New("tint_continue");
                    auto* decl = b.Decl(b.Var(var_name, b.ty.bool_(), b.Expr(false)));
                    auto ip = utils::GetInsertionPoint(ctx, switch_stmt);
                    ctx.InsertBefore(ip.first->Declaration()->statements, ip.second, decl);

                    // Create and insert 'if (tint_continue) { continue; }' after
                    // switch.
                    auto* if_stmt = b.If(b.Expr(var_name), b.Block(b.Continue()));
                    ctx.InsertAfter(ip.first->Declaration()->statements, ip.second, if_stmt);

                    // Return the new var name
                    return var_name;
                });

            // Replace 'continue;' with '{ tint_continue = true; break; }'
            auto* new_stmt = b.Block(                   //
                b.Assign(b.Expr(cont_var_name), true),  //
                b.Break());

            ctx.Replace(cont, new_stmt);
        }

        ctx.Clone();
    }
};

}  // namespace

RemoveContinueInSwitch::RemoveContinueInSwitch() = default;
RemoveContinueInSwitch::~RemoveContinueInSwitch() = default;

bool RemoveContinueInSwitch::ShouldRun(const Program* program, const DataMap& /*data*/) const {
    return State::ShouldRun(program);
}

void RemoveContinueInSwitch::Run(CloneContext& ctx, const DataMap&, DataMap&) const {
    State state(ctx);
    state.Run();
}

}  // namespace tint::transform