/// <summary>
/// Determine whether it matters if an expression is run before or after another sequence of statements/expressions
/// </summary>
public static bool DoesOrderMatter(JsExpression expr1, ExpressionCompileResult expr2)
{
// The algorithm is rather simple and conservative: For the both expression (sequences), determine a) which locals are read, b) which locals are written, and c) whether can possibly read or write any external state.
// The order of the two expressions then matters if and only if:
// 1) Either expression writes a local that the other uses,
// 2) The expressions write to the same locals, or
// 3) Both the expressions use any external state.
var v1 = new FindObservableStateVisitor();
v1.VisitExpression(expr1, null);
var v2 = new FindObservableStateVisitor();
foreach (var s in expr2.AdditionalStatements)
{
v2.VisitStatement(s, null);
}
v2.VisitExpression(expr2.Expression, null);
if (v1.Result.LocalReadSet.Overlaps(v2.Result.LocalWriteSet) || v1.Result.LocalWriteSet.Overlaps(v2.Result.LocalReadSet))
{
return(true);
}
if (v1.Result.LocalWriteSet.Overlaps(v2.Result.LocalWriteSet))
{
return(true);
}
if (v1.Result.UsesExternalState && v2.Result.UsesExternalState)
{
return(true);
}
return(false);
}
public static void CreateTemporariesForAllExpressionsThatHaveToBeEvaluatedBeforeNewExpression(IList<JsStatement> statementList, IList<JsExpression> expressions, ExpressionCompileResult newExpressions, Func<string> createTemporaryVariable) {
for (int i = 0; i < expressions.Count; i++) {
if (ExpressionOrderer.DoesOrderMatter(expressions[i], newExpressions)) {
var temp = createTemporaryVariable();
statementList.Add(new JsVariableDeclarationStatement(temp, expressions[i]));
expressions[i] = JsExpression.Identifier(temp);
}
}
}
