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// Copyright 2021 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/transform/loop_to_for_loop.h"
#include "src/ast/break_statement.h"
#include "src/ast/for_loop_statement.h"
#include "src/program_builder.h"
#include "src/sem/block_statement.h"
#include "src/sem/function.h"
#include "src/sem/statement.h"
#include "src/sem/variable.h"
#include "src/utils/scoped_assignment.h"
TINT_INSTANTIATE_TYPEINFO(tint::transform::LoopToForLoop);
namespace tint {
namespace transform {
namespace {
bool IsBlockWithSingleBreak(const ast::BlockStatement* block) {
if (block->statements.size() != 1) {
return false;
}
return block->statements[0]->Is<ast::BreakStatement>();
}
bool IsVarUsedByStmt(const sem::Info& sem,
const ast::Variable* var,
const ast::Statement* stmt) {
auto* var_sem = sem.Get(var);
for (auto* user : var_sem->Users()) {
if (auto* s = user->Stmt()) {
if (s->Declaration() == stmt) {
return true;
}
}
}
return false;
}
} // namespace
LoopToForLoop::LoopToForLoop() = default;
LoopToForLoop::~LoopToForLoop() = default;
bool LoopToForLoop::ShouldRun(const Program* program, const DataMap&) const {
for (auto* node : program->ASTNodes().Objects()) {
if (node->Is<ast::LoopStatement>()) {
return true;
}
}
return false;
}
void LoopToForLoop::Run(CloneContext& ctx, const DataMap&, DataMap&) const {
ctx.ReplaceAll([&](const ast::LoopStatement* loop) -> const ast::Statement* {
// For loop condition is taken from the first statement in the loop.
// This requires an if-statement with either:
// * A true block with no else statements, and the true block contains a
// single 'break' statement.
// * An empty true block with a single, no-condition else statement
// containing a single 'break' statement.
// Examples:
// loop { if (condition) { break; } ... }
// loop { if (condition) {} else { break; } ... }
auto& stmts = loop->body->statements;
if (stmts.empty()) {
return nullptr;
}
auto* if_stmt = stmts[0]->As<ast::IfStatement>();
if (!if_stmt) {
return nullptr;
}
bool negate_condition = false;
if (IsBlockWithSingleBreak(if_stmt->body) &&
if_stmt->else_statements.empty()) {
negate_condition = true;
} else if (if_stmt->body->Empty() && if_stmt->else_statements.size() == 1 &&
if_stmt->else_statements[0]->condition == nullptr &&
IsBlockWithSingleBreak(if_stmt->else_statements[0]->body)) {
negate_condition = false;
} else {
return nullptr;
}
// The continuing block must be empty or contain a single, assignment or
// function call statement.
const ast::Statement* continuing = nullptr;
if (auto* loop_cont = loop->continuing) {
if (loop_cont->statements.size() != 1) {
return nullptr;
}
continuing = loop_cont->statements[0];
if (!continuing
->IsAnyOf<ast::AssignmentStatement, ast::CallStatement>()) {
return nullptr;
}
// And the continuing statement must not use any of the variables declared
// in the loop body.
for (auto* stmt : loop->body->statements) {
if (auto* var_decl = stmt->As<ast::VariableDeclStatement>()) {
if (IsVarUsedByStmt(ctx.src->Sem(), var_decl->variable, continuing)) {
return nullptr;
}
}
}
continuing = ctx.Clone(continuing);
}
auto* condition = ctx.Clone(if_stmt->condition);
if (negate_condition) {
condition = ctx.dst->create<ast::UnaryOpExpression>(ast::UnaryOp::kNot,
condition);
}
ast::Statement* initializer = nullptr;
ctx.Remove(loop->body->statements, if_stmt);
auto* body = ctx.Clone(loop->body);
return ctx.dst->create<ast::ForLoopStatement>(initializer, condition,
continuing, body);
});
ctx.Clone();
}
} // namespace transform
} // namespace tint