public override void Visit(Conditional node)
{
if (node != null)
{
// we have two choices for the conditional. Either:
// 1. we wrap the whole thing in a logical-not operator, which means we also need to
// add parentheses, since conditional is lower-precedence than the logicial not, or
// 2. apply the logical-not to both the true- and false-branches.
// The first is guaranteed 3 additional characters. We have to check the delta for
// each branch and add them together to know how much the second would cost. If it's
// greater than 3, then we just want to not the whole thing.
var notTrue = new LogicalNot(node.TrueExpression, m_parser);
var notFalse = new LogicalNot(node.FalseExpression, m_parser);
var costNottingBoth = notTrue.Measure() + notFalse.Measure();
if (m_measure)
{
// we're just measuring -- adjust the delta accordingly
// (the lesser of the two options)
m_delta += (costNottingBoth > 3) ? 3 : costNottingBoth;
}
else if (costNottingBoth > 3)
{
// just wrap the whole thing
WrapWithLogicalNot(node);
}
else
{
// less bytes to wrap each branch separately
node.TrueExpression.Accept(this);
node.FalseExpression.Accept(this);
}
}
}
public override void Visit(Conditional node)
{
if (node != null)
{
// we have two choices for the conditional. Either:
// 1. we wrap the whole thing in a logical-not operator, which means we also need to
// add parentheses, since conditional is lower-precedence than the logicial not, or
// 2. apply the logical-not to both the true- and false-branches.
// The first is guaranteed 3 additional characters. We have to check the delta for
// each branch and add them together to know how much the second would cost. If it's
// greater than 3, then we just want to not the whole thing.
var notTrue = new LogicalNot(node.TrueExpression, m_parser);
var notFalse = new LogicalNot(node.FalseExpression, m_parser);
var costNottingBoth = notTrue.Measure() + notFalse.Measure();
if (m_measure)
{
// we're just measuring -- adjust the delta accordingly
// (the lesser of the two options)
m_delta += (costNottingBoth > 3) ? 3 : costNottingBoth;
}
else if (costNottingBoth > 3)
{
// just wrap the whole thing
WrapWithLogicalNot(node);
}
else
{
// less bytes to wrap each branch separately
node.TrueExpression.Accept(this);
node.FalseExpression.Accept(this);
}
}
}
private void IfConditionExpressionToExpression(IfNode ifNode, AstNode expression)
{
// but first -- which operator to use? if(a)b --> a&&b, and if(!a)b --> a||b
// so determine which one is smaller: a or !a
// assume we'll use the logical-and, since that doesn't require changing the condition
var newOperator = JSToken.LogicalAnd;
var logicalNot = new LogicalNot(ifNode.Condition, m_parser);
if (logicalNot.Measure() < 0)
{
// !a is smaller, so apply it and use the logical-or operator
logicalNot.Apply();
newOperator = JSToken.LogicalOr;
}
// because the true block is an expression, we know it must only have
// ONE statement in it, so we can just dereference it directly.
var binaryOp = new BinaryOperator(ifNode.Context, m_parser)
{
Operand1 = ifNode.Condition,
Operand2 = expression,
OperatorToken = newOperator,
};
// we don't need to analyse this new node because we've already analyzed
// the pieces parts as part of the if. And this visitor's method for the BinaryOperator
// doesn't really do anything else. Just replace our current node with this
// new node
ifNode.Parent.ReplaceChild(ifNode, binaryOp);
}
public override void Visit(BinaryOperator node)
{
if (node != null)
{
base.Visit(node);
// see if this operation is subtracting zero from a lookup -- that is typically done to
// coerce a value to numeric. There's a simpler way: unary plus operator.
if (node.OperatorToken == JSToken.Minus
&& m_parser.Settings.IsModificationAllowed(TreeModifications.SimplifyStringToNumericConversion))
{
Lookup lookup = node.Operand1 as Lookup;
if (lookup != null)
{
ConstantWrapper right = node.Operand2 as ConstantWrapper;
if (right != null && right.IsIntegerLiteral && right.ToNumber() == 0)
{
// okay, so we have "lookup - 0"
// this is done frequently to force a value to be numeric.
// There is an easier way: apply the unary + operator to it.
// transform: lookup - 0 => +lookup
var unary = new UnaryOperator(node.Context, m_parser)
{
Operand = lookup,
OperatorToken = JSToken.Plus
};
node.Parent.ReplaceChild(node, unary);
// because we recursed at the top of this function, we don't need to Analyze
// the new Unary node. This visitor's method for UnaryOperator only does something
// if the operand is a constant -- and this one is a Lookup. And we already analyzed
// the lookup.
}
}
}
else if ((node.OperatorToken == JSToken.StrictEqual || node.OperatorToken == JSToken.StrictNotEqual)
&& m_parser.Settings.IsModificationAllowed(TreeModifications.ReduceStrictOperatorIfTypesAreSame))
{
PrimitiveType leftType = node.Operand1.FindPrimitiveType();
if (leftType != PrimitiveType.Other)
{
PrimitiveType rightType = node.Operand2.FindPrimitiveType();
if (leftType == rightType)
{
// the are the same known types. We can reduce the operators
node.OperatorToken = node.OperatorToken == JSToken.StrictEqual ? JSToken.Equal : JSToken.NotEqual;
}
else if (rightType != PrimitiveType.Other)
{
// they are not the same, but they are both known. We can completely remove the operator
// and replace it with true (!==) or false (===).
// transform: x !== y => true
// transform: x === y => false
node.Context.HandleError(JSError.StrictComparisonIsAlwaysTrueOrFalse, false);
node.Parent.ReplaceChild(
node,
new ConstantWrapper(node.OperatorToken == JSToken.StrictNotEqual, PrimitiveType.Boolean, node.Context, m_parser));
// because we are essentially removing the node from the AST, be sure to detach any references
DetachReferences.Apply(node);
}
}
}
else if (node.IsAssign)
{
var lookup = node.Operand1 as Lookup;
if (lookup != null)
{
if (lookup.VariableField != null && lookup.VariableField.InitializationOnly)
{
// the field is an initialization-only field -- we should NOT be assigning to it
lookup.Context.HandleError(JSError.AssignmentToConstant, true);
}
else if (m_scopeStack.Peek().UseStrict)
{
if (lookup.VariableField == null || lookup.VariableField.FieldType == FieldType.UndefinedGlobal)
{
// strict mode cannot assign to undefined fields
node.Operand1.Context.HandleError(JSError.StrictModeUndefinedVariable, true);
}
else if(lookup.VariableField.FieldType == FieldType.Arguments
|| (lookup.VariableField.FieldType == FieldType.Predefined && string.CompareOrdinal(lookup.Name, "eval") == 0))
{
// strict mode cannot assign to lookup "eval" or "arguments"
node.Operand1.Context.HandleError(JSError.StrictModeInvalidAssign, true);
}
}
}
}
else if ((node.Parent is Block || (node.Parent is CommaOperator && node.Parent.Parent is Block))
&& (node.OperatorToken == JSToken.LogicalOr || node.OperatorToken == JSToken.LogicalAnd))
{
// this is an expression statement where the operator is || or && -- basically
// it's a shortcut for an if-statement:
// expr1&&expr2; ==> if(expr1)expr2;
// expr1||expr2; ==> if(!expr1)expr2;
// let's check to see if the not of expr1 is smaller. If so, we can not the expression
// and change the operator
var logicalNot = new LogicalNot(node.Operand1, node.Parser);
if (logicalNot.Measure() < 0)
{
// it would be smaller! Change it.
// transform: expr1&&expr2 => !expr1||expr2
// transform: expr1||expr2 => !expr1&&expr2
logicalNot.Apply();
node.OperatorToken = node.OperatorToken == JSToken.LogicalAnd ? JSToken.LogicalOr : JSToken.LogicalAnd;
}
}
}
}
public override void Visit(IfNode node)
{
if (node != null)
{
if (m_parser.Settings.StripDebugStatements
&& m_parser.Settings.IsModificationAllowed(TreeModifications.StripDebugStatements))
{
if (node.TrueBlock != null && node.TrueBlock.IsDebuggerStatement)
{
node.TrueBlock = null;
}
if (node.FalseBlock != null && node.FalseBlock.IsDebuggerStatement)
{
node.FalseBlock = null;
}
}
// recurse....
base.Visit(node);
// now check to see if the two branches are now empty.
// if they are, null them out.
if (node.TrueBlock != null && node.TrueBlock.Count == 0)
{
node.TrueBlock = null;
}
if (node.FalseBlock != null && node.FalseBlock.Count == 0)
{
node.FalseBlock = null;
}
if (node.TrueBlock != null && node.FalseBlock != null)
{
// neither true block nor false block is null.
// if they're both expressions, convert them to a condition operator
if (node.TrueBlock.IsExpression && node.FalseBlock.IsExpression
&& m_parser.Settings.IsModificationAllowed(TreeModifications.IfExpressionsToExpression))
{
// if this statement has both true and false blocks, and they are both expressions,
// then we can simplify this to a conditional expression.
// because the blocks are expressions, we know they only have ONE statement in them,
// so we can just dereference them directly.
Conditional conditional;
var logicalNot = new LogicalNot(node.Condition, m_parser);
if (logicalNot.Measure() < 0)
{
// applying a logical-not makes the condition smaller -- reverse the branches
logicalNot.Apply();
conditional = new Conditional(node.Context, m_parser)
{
Condition = node.Condition,
TrueExpression = node.FalseBlock[0],
FalseExpression = node.TrueBlock[0]
};
}
else
{
// regular order
conditional = new Conditional(node.Context, m_parser)
{
Condition = node.Condition,
TrueExpression = node.TrueBlock[0],
FalseExpression = node.FalseBlock[0]
};
}
node.Parent.ReplaceChild(
node,
conditional);
Optimize(conditional);
}
else
{
// see if logical-notting the condition produces something smaller
var logicalNot = new LogicalNot(node.Condition, m_parser);
if (logicalNot.Measure() < 0)
{
// it does -- not the condition and swap the branches
logicalNot.Apply();
node.SwapBranches();
}
// see if the true- and false-branches each contain only a single statement
if (node.TrueBlock.Count == 1 && node.FalseBlock.Count == 1)
{
// they do -- see if the true-branch's statement is a return-statement
var trueReturn = node.TrueBlock[0] as ReturnNode;
if (trueReturn != null && trueReturn.Operand != null)
{
// it is -- see if the false-branch is also a return statement
var falseReturn = node.FalseBlock[0] as ReturnNode;
if (falseReturn != null && falseReturn.Operand != null)
{
// transform: if(cond)return expr1;else return expr2 to return cond?expr1:expr2
var conditional = new Conditional(null, m_parser)
{
Condition = node.Condition,
TrueExpression = trueReturn.Operand,
FalseExpression = falseReturn.Operand
};
// create a new return node from the conditional and replace
// our if-node with it
var returnNode = new ReturnNode(node.Context, m_parser)
{
Operand = conditional
};
node.Parent.ReplaceChild(
node,
returnNode);
Optimize(conditional);
}
}
}
}
}
else if (node.FalseBlock != null)
{
// true block must be null.
// if there is no true branch but a false branch, then
// put a not on the condition and move the false branch to the true branch.
if (node.FalseBlock.IsExpression
&& m_parser.Settings.IsModificationAllowed(TreeModifications.IfConditionCallToConditionAndCall))
{
// if (cond); else expr ==> cond || expr
// but first -- which operator to use? if(a);else b --> a||b, and if(!a);else b --> a&&b
// so determine which one is smaller: a or !a
// assume we'll use the logical-or, since that doesn't require changing the condition
var newOperator = JSToken.LogicalOr;
var logicalNot = new LogicalNot(node.Condition, m_parser);
if (logicalNot.Measure() < 0)
{
// !a is smaller, so apply it and use the logical-or operator
logicalNot.Apply();
newOperator = JSToken.LogicalAnd;
}
var binaryOp = new BinaryOperator(node.Context, m_parser)
{
Operand1 = node.Condition,
Operand2 = node.FalseBlock[0],
OperatorToken = newOperator,
};
// we don't need to analyse this new node because we've already analyzed
// the pieces parts as part of the if. And this visitor's method for the BinaryOperator
// doesn't really do anything else. Just replace our current node with this
// new node
node.Parent.ReplaceChild(node, binaryOp);
}
else if (m_parser.Settings.IsModificationAllowed(TreeModifications.IfConditionFalseToIfNotConditionTrue))
{
// logical-not the condition
// if(cond);else stmt ==> if(!cond)stmt
var logicalNot = new LogicalNot(node.Condition, m_parser);
logicalNot.Apply();
// and swap the branches
node.SwapBranches();
}
}
else if (node.TrueBlock != null)
{
// false block must be null
if (node.TrueBlock.IsExpression
&& m_parser.Settings.IsModificationAllowed(TreeModifications.IfConditionCallToConditionAndCall))
{
// convert the if-node to an expression
IfConditionExpressionToExpression(node, node.TrueBlock[0]);
}
}
else if (m_parser.Settings.IsModificationAllowed(TreeModifications.IfEmptyToExpression))
{
// NEITHER branches have anything now!
// as long as the condition doesn't
// contain calls or assignments, we should be able to completely delete
// the statement altogether rather than changing it to an expression
// statement on the condition.
// but how do we KNOW there are no side-effects?
// if the condition is a constant or operations on constants, delete it.
// or if the condition itself is a debugger statement -- a call, lookup, or member.
var remove = node.Condition.IsConstant || node.Condition.IsDebuggerStatement;
if (remove)
{
// we're pretty sure there are no side-effects; remove it altogether
node.Parent.ReplaceChild(node, null);
}
else
{
// We don't know what it is and what the side-effects may be, so
// just change this statement into an expression statement by replacing us with
// the expression
// no need to analyze -- we already recursed
node.Parent.ReplaceChild(node, node.Condition);
}
}
if (node.FalseBlock == null
&& node.TrueBlock != null
&& node.TrueBlock.Count == 1
&& m_parser.Settings.IsModificationAllowed(TreeModifications.CombineNestedIfs))
{
var nestedIf = node.TrueBlock[0] as IfNode;
if (nestedIf != null && nestedIf.FalseBlock == null)
{
// we have nested if-blocks.
// transform if(cond1)if(cond2){...} to if(cond1&&cond2){...}
// change the first if-statement's condition to be cond1&&cond2
// move the nested if-statement's true block to the outer if-statement
node.Condition = new BinaryOperator(null, m_parser)
{
Operand1 = node.Condition,
Operand2 = nestedIf.Condition,
OperatorToken = JSToken.LogicalAnd
};
node.TrueBlock = nestedIf.TrueBlock;
}
}
}
}
