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Closure Compiler is a JavaScript optimizing compiler. It parses your
JavaScript, analyzes it, removes dead code and rewrites and minimizes
what's left. It also checks syntax, variable references, and types, and
warns about common JavaScript pitfalls. It is used in many of Google's
JavaScript apps, including Gmail, Google Web Search, Google Maps, and
Google Docs.
/*
* Copyright 2004 The Closure Compiler 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.
*/
package com.google.javascript.jscomp;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import com.google.javascript.jscomp.NodeUtil.ValueType;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import com.google.javascript.rhino.jstype.TernaryValue;
/**
* Peephole optimization to fold constants (e.g. x + 1 + 7 --> x + 8).
*/
class PeepholeFoldConstants extends AbstractPeepholeOptimization {
// TODO(johnlenz): optimizations should not be emiting errors. Move these to
// a check pass.
static final DiagnosticType INVALID_GETELEM_INDEX_ERROR =
DiagnosticType.warning(
"JSC_INVALID_GETELEM_INDEX_ERROR",
"Array index not integer: {0}");
static final DiagnosticType FRACTIONAL_BITWISE_OPERAND =
DiagnosticType.warning(
"JSC_FRACTIONAL_BITWISE_OPERAND",
"Fractional bitwise operand: {0}");
private static final double MAX_FOLD_NUMBER = Math.pow(2, 53);
private final boolean late;
private final boolean shouldUseTypes;
/**
* @param late When late is false, this mean we are currently running before
* most of the other optimizations. In this case we would avoid optimizations
* that would make the code harder to analyze. When this is true, we would
* do anything to minimize for size.
*/
PeepholeFoldConstants(boolean late, boolean shouldUseTypes) {
this.late = late;
this.shouldUseTypes = shouldUseTypes;
}
@Override
Node optimizeSubtree(Node subtree) {
switch (subtree.getToken()) {
case CALL:
return tryFoldCall(subtree);
case NEW:
return tryFoldCtorCall(subtree);
case TYPEOF:
return tryFoldTypeof(subtree);
case ARRAYLIT:
case OBJECTLIT:
return tryFlattenArrayOrObjectLit(subtree);
case NOT:
case POS:
case NEG:
case BITNOT:
tryReduceOperandsForOp(subtree);
return tryFoldUnaryOperator(subtree);
case VOID:
return tryReduceVoid(subtree);
default:
tryReduceOperandsForOp(subtree);
return tryFoldBinaryOperator(subtree);
}
}
private Node tryFoldBinaryOperator(Node subtree) {
Node left = subtree.getFirstChild();
if (left == null) {
return subtree;
}
Node right = left.getNext();
if (right == null) {
return subtree;
}
// If we've reached here, node is truly a binary operator.
switch (subtree.getToken()) {
case GETPROP:
return tryFoldGetProp(subtree, left, right);
case GETELEM:
return tryFoldGetElem(subtree, left, right);
case INSTANCEOF:
return tryFoldInstanceof(subtree, left, right);
case AND:
case OR:
return tryFoldAndOr(subtree, left, right);
case COALESCE:
return tryFoldCoalesce(subtree, left, right);
case LSH:
case RSH:
case URSH:
return tryFoldShift(subtree, left, right);
case ASSIGN:
return tryFoldAssign(subtree, left, right);
case ASSIGN_BITOR:
case ASSIGN_BITXOR:
case ASSIGN_BITAND:
case ASSIGN_LSH:
case ASSIGN_RSH:
case ASSIGN_URSH:
case ASSIGN_ADD:
case ASSIGN_SUB:
case ASSIGN_MUL:
case ASSIGN_DIV:
case ASSIGN_MOD:
case ASSIGN_EXPONENT:
return tryUnfoldAssignOp(subtree, left, right);
case ADD:
return tryFoldAdd(subtree, left, right);
case SUB:
case DIV:
case MOD:
case EXPONENT:
return tryFoldArithmeticOp(subtree, left, right);
case MUL:
case BITAND:
case BITOR:
case BITXOR:
Node result = tryFoldArithmeticOp(subtree, left, right);
if (result != subtree) {
return result;
}
return tryFoldLeftChildOp(subtree, left, right);
case LT:
case GT:
case LE:
case GE:
case EQ:
case NE:
case SHEQ:
case SHNE:
return tryFoldComparison(subtree, left, right);
default:
return subtree;
}
}
private Node tryReduceVoid(Node n) {
Node child = n.getFirstChild();
if ((!child.isNumber() || child.getDouble() != 0.0) && !mayHaveSideEffects(n)) {
n.replaceChild(child, IR.number(0));
reportChangeToEnclosingScope(n);
}
return n;
}
private void tryReduceOperandsForOp(Node n) {
switch (n.getToken()) {
case ADD:
Node left = n.getFirstChild();
Node right = n.getLastChild();
if (!NodeUtil.mayBeString(left, shouldUseTypes)
&& !NodeUtil.mayBeString(right, shouldUseTypes)) {
tryConvertOperandsToNumber(n);
}
break;
case ASSIGN_BITOR:
case ASSIGN_BITXOR:
case ASSIGN_BITAND:
// TODO(johnlenz): convert these to integers.
case ASSIGN_LSH:
case ASSIGN_RSH:
case ASSIGN_URSH:
case ASSIGN_SUB:
case ASSIGN_MUL:
case ASSIGN_MOD:
case ASSIGN_DIV:
tryConvertToNumber(n.getLastChild());
break;
case BITNOT:
case BITOR:
case BITXOR:
case BITAND:
case LSH:
case RSH:
case URSH:
case SUB:
case MUL:
case MOD:
case DIV:
case POS:
case NEG:
case EXPONENT:
tryConvertOperandsToNumber(n);
break;
default:
break;
}
}
private void tryConvertOperandsToNumber(Node n) {
Node next;
for (Node c = n.getFirstChild(); c != null; c = next) {
next = c.getNext();
tryConvertToNumber(c);
}
}
private void tryConvertToNumber(Node n) {
switch (n.getToken()) {
case NUMBER:
// Nothing to do
return;
case AND:
case OR:
case COMMA:
case COALESCE:
tryConvertToNumber(n.getLastChild());
return;
case HOOK:
tryConvertToNumber(n.getSecondChild());
tryConvertToNumber(n.getLastChild());
return;
case NAME:
if (!NodeUtil.isUndefined(n)) {
return;
}
break;
default:
break;
}
Double result = getSideEffectFreeNumberValue(n);
if (result == null) {
return;
}
double value = result;
Node replacement = NodeUtil.numberNode(value, n);
if (replacement.isEquivalentTo(n)) {
return;
}
n.replaceWith(replacement);
reportChangeToEnclosingScope(replacement);
}
/**
* Folds 'typeof(foo)' if foo is a literal, e.g.
* typeof("bar") --> "string"
* typeof(6) --> "number"
*/
private Node tryFoldTypeof(Node originalTypeofNode) {
checkArgument(originalTypeofNode.isTypeOf());
Node argumentNode = originalTypeofNode.getFirstChild();
if (argumentNode == null || !NodeUtil.isLiteralValue(argumentNode, true)) {
return originalTypeofNode;
}
String typeNameString = null;
switch (argumentNode.getToken()) {
case FUNCTION:
typeNameString = "function";
break;
case STRING:
typeNameString = "string";
break;
case NUMBER:
typeNameString = "number";
break;
case TRUE:
case FALSE:
typeNameString = "boolean";
break;
case NULL:
case OBJECTLIT:
case ARRAYLIT:
typeNameString = "object";
break;
case VOID:
typeNameString = "undefined";
break;
case NAME:
// We assume here that programs don't change the value of the
// keyword undefined to something other than the value undefined.
if ("undefined".equals(argumentNode.getString())) {
typeNameString = "undefined";
}
break;
default:
break;
}
if (typeNameString != null) {
Node newNode = IR.string(typeNameString);
reportChangeToEnclosingScope(originalTypeofNode);
originalTypeofNode.replaceWith(newNode);
markFunctionsDeleted(originalTypeofNode);
return newNode;
}
return originalTypeofNode;
}
private Node tryFoldUnaryOperator(Node n) {
checkState(n.hasOneChild(), n);
Node left = n.getFirstChild();
Node parent = n.getParent();
if (left == null) {
return n;
}
TernaryValue leftVal = getSideEffectFreeBooleanValue(left);
if (leftVal == TernaryValue.UNKNOWN) {
return n;
}
switch (n.getToken()) {
case NOT:
// Don't fold !0 and !1 back to false.
if (late && left.isNumber()) {
double numValue = left.getDouble();
if (numValue == 0 || numValue == 1) {
return n;
}
}
Node replacementNode = NodeUtil.booleanNode(!leftVal.toBoolean(true));
parent.replaceChild(n, replacementNode);
reportChangeToEnclosingScope(parent);
return replacementNode;
case POS:
if (NodeUtil.isNumericResult(left)) {
// POS does nothing to numeric values.
parent.replaceChild(n, left.detach());
reportChangeToEnclosingScope(parent);
return left;
}
return n;
case NEG:
if (left.isName()) {
if (left.getString().equals("Infinity")) {
// "-Infinity" is valid and a literal, don't modify it.
return n;
} else if (left.getString().equals("NaN")) {
// "-NaN" is "NaN".
n.removeChild(left);
parent.replaceChild(n, left);
reportChangeToEnclosingScope(parent);
return left;
}
}
if (left.isNumber()) {
double negNum = -left.getDouble();
Node negNumNode = IR.number(negNum);
parent.replaceChild(n, negNumNode);
reportChangeToEnclosingScope(parent);
return negNumNode;
}
return n;
case BITNOT:
if (left.isNumber()) {
double val = left.getDouble();
if (Math.floor(val) == val) {
int intVal = jsConvertDoubleToBits(val);
Node notIntValNode = IR.number(~intVal);
parent.replaceChild(n, notIntValNode);
reportChangeToEnclosingScope(parent);
return notIntValNode;
} else {
report(FRACTIONAL_BITWISE_OPERAND, left);
return n;
}
} else {
return n;
}
default:
return n;
}
}
/**
* Uses a method for treating a double as 32bits that is equivalent to
* how JavaScript would convert a number before applying a bit operation.
*/
private int jsConvertDoubleToBits(double d) {
return (int) (((long) Math.floor(d)) & 0xffffffff);
}
/**
* Try to fold {@code left instanceof right} into {@code true}
* or {@code false}.
*/
private Node tryFoldInstanceof(Node n, Node left, Node right) {
checkArgument(n.isInstanceOf());
// TODO(johnlenz) Use type information if available to fold
// instanceof.
if (NodeUtil.isLiteralValue(left, true)
&& !mayHaveSideEffects(right)) {
Node replacementNode = null;
if (NodeUtil.isImmutableValue(left)) {
// Non-object types are never instances.
replacementNode = IR.falseNode();
} else if (right.isName()
&& "Object".equals(right.getString())) {
replacementNode = IR.trueNode();
}
if (replacementNode != null) {
n.replaceWith(replacementNode);
reportChangeToEnclosingScope(replacementNode);
markFunctionsDeleted(n);
return replacementNode;
}
}
return n;
}
private Node tryFoldAssign(Node n, Node left, Node right) {
checkArgument(n.isAssign());
if (!late) {
return n;
}
// Tries to convert x = x + y -> x += y;
if (!right.hasChildren() || right.getSecondChild() != right.getLastChild()) {
// RHS must have two children.
return n;
}
if (mayHaveSideEffects(left)) {
return n;
}
Node newRight;
if (areNodesEqualForInlining(left, right.getFirstChild())) {
newRight = right.getLastChild();
} else if (NodeUtil.isCommutative(right.getToken())
&& areNodesEqualForInlining(left, right.getLastChild())) {
newRight = right.getFirstChild();
} else {
return n;
}
Token newType = null;
switch (right.getToken()) {
case ADD:
newType = Token.ASSIGN_ADD;
break;
case BITAND:
newType = Token.ASSIGN_BITAND;
break;
case BITOR:
newType = Token.ASSIGN_BITOR;
break;
case BITXOR:
newType = Token.ASSIGN_BITXOR;
break;
case DIV:
newType = Token.ASSIGN_DIV;
break;
case LSH:
newType = Token.ASSIGN_LSH;
break;
case MOD:
newType = Token.ASSIGN_MOD;
break;
case MUL:
newType = Token.ASSIGN_MUL;
break;
case RSH:
newType = Token.ASSIGN_RSH;
break;
case SUB:
newType = Token.ASSIGN_SUB;
break;
case URSH:
newType = Token.ASSIGN_URSH;
break;
case EXPONENT:
newType = Token.ASSIGN_EXPONENT;
break;
default:
return n;
}
Node newNode = new Node(newType,
left.detach(), newRight.detach());
n.replaceWith(newNode);
reportChangeToEnclosingScope(newNode);
return newNode;
}
private Node tryUnfoldAssignOp(Node n, Node left, Node right) {
if (late) {
return n;
}
if (!n.hasChildren() || n.getSecondChild() != n.getLastChild()) {
return n;
}
if (mayHaveSideEffects(left)) {
return n;
}
// Tries to convert x += y -> x = x + y;
Token op = NodeUtil.getOpFromAssignmentOp(n);
Node replacement = IR.assign(left.detach(),
new Node(op, left.cloneTree(), right.detach())
.srcref(n));
n.replaceWith(replacement);
reportChangeToEnclosingScope(replacement);
return replacement;
}
/**
* Try to fold a AND/OR node.
*/
private Node tryFoldAndOr(Node n, Node left, Node right) {
Node parent = n.getParent();
Node result = null;
Node dropped = null;
Token type = n.getToken();
TernaryValue leftVal = NodeUtil.getBooleanValue(left);
if (leftVal != TernaryValue.UNKNOWN) {
boolean lval = leftVal.toBoolean(true);
// (TRUE || x) => TRUE (also, (3 || x) => 3)
// (FALSE && x) => FALSE
if ((lval && type == Token.OR) || (!lval && type == Token.AND)) {
result = left;
dropped = right;
} else if (!mayHaveSideEffects(left)) {
// (FALSE || x) => x
// (TRUE && x) => x
result = right;
dropped = left;
} else {
// Left side may have side effects, but we know its boolean value.
// e.g. true_with_sideeffects || foo() => true_with_sideeffects, foo()
// or: false_with_sideeffects && foo() => false_with_sideeffects, foo()
// This, combined with PeepholeRemoveDeadCode, helps reduce expressions
// like "x() || false || z()".
n.detachChildren();
result = IR.comma(left, right);
dropped = null;
}
} else if (parent.getToken() == type && n == parent.getFirstChild()) {
TernaryValue rightValue = NodeUtil.getBooleanValue(right);
if (!mayHaveSideEffects(right)) {
if ((rightValue == TernaryValue.FALSE && type == Token.OR)
|| (rightValue == TernaryValue.TRUE && type == Token.AND)) {
result = left;
dropped = right;
}
}
}
// Note: Right hand side folding is handled by
// PeepholeMinimizeConditions#tryMinimizeCondition
if (result != null) {
// Fold it!
n.detachChildren();
parent.replaceChild(n, result);
reportChangeToEnclosingScope(result);
if (dropped != null) {
markFunctionsDeleted(dropped);
}
return result;
} else {
return n;
}
}
/** Try to fold a COALESCE node. */
private Node tryFoldCoalesce(Node n, Node left, Node right) {
Node parent = n.getParent();
Node result = null;
Node dropped = null;
TernaryValue leftVal = NodeUtil.getBooleanValue(left);
if (leftVal != TernaryValue.UNKNOWN) {
if (NodeUtil.isNullOrUndefined(left)) {
result = right;
dropped = left;
} else {
if (!mayHaveSideEffects(left)) {
result = left;
dropped = right;
} else {
n.detachChildren();
result = IR.comma(left, right);
dropped = null;
}
}
}
if (result != null) {
// Fold!
n.detachChildren();
parent.replaceChild(n, result);
reportChangeToEnclosingScope(result);
if (dropped != null) {
markFunctionsDeleted(dropped);
}
return result;
} else {
return n;
}
}
/**
* Takes a subtree representing an expression of chained addition between expressions and folds
* adjacent string addition when possible and safe.
*
* @param n root node of ADD expression to be optimized
* @param left left child of n being added
* @param right right child of n being added
* @return AST subtree starting from n that has been optimized to collapse the rightmost left
* child leaf node which must be a string literal and the leftmost right child leaf node if
* possible to do so in a type safe way.
*/
private Node tryFoldAdjacentLiteralLeaves(Node n, Node left, Node right) {
// Find left child's rightmost leaf
Node leftParent = n;
Node rightParent = n;
while (left.isAdd()) {
// This had better be in a chain of '+' operations
leftParent = left;
left = left.getSecondChild();
}
// Find right child's leftmost leaf
while (right.isAdd()) {
// This had better be in a chain of '+' operations
rightParent = right;
right = right.getFirstChild();
}
// Try to fold if of the form:
// ... + +
// ... + + ( + ...)
// aka. when the literal might be collapsible into the string
if (leftParent.isAdd()
&& left.isString()
&& rightParent.isAdd()
&& NodeUtil.isLiteralValue(right, /* includeFunctions= */ false)) {
Node rightGrandparent = rightParent.getParent();
// `rr` is righthand side term that `right` is being added to and is null if right is still
// the second child of `n` being added to `left` and non-null if it is in a nested add expr
Node rr = right.getNext();
boolean foldIsTypeSafe =
// If right.getNext() is already a string, folding won't disturb any typecasting
(rr != null && NodeUtil.isStringResult(rr))
|| (rr != null
// If right.getNext() isn't a string result, right must be a string to be folded
&& right.isString()
// Access the right grandparent safely...
&& rightGrandparent != null
&& rightGrandparent.isAdd()
// The second child of `rightGrandparent` is what `right + rr` is being added to.
// If it exists, `right` can only be safely removed if `rr` is still treated as a
// string in the resulting addition.
&& NodeUtil.isStringResult(rightGrandparent.getSecondChild()))
// Dangling literal term has no typecasting side effects; fold it!
|| (rr == null);
if (foldIsTypeSafe) {
String result = left.getString() + NodeUtil.getStringValue(right);
// If the right parent is the root, shift the left parent up so as not to overwrite the tree
// Otherwise, shift the right parent up
if (rightParent.getSecondChild().equals(right)) {
left.replaceWith(IR.string(result));
replace(rightParent, rightParent.getFirstChild().cloneTree(true));
} else {
left.replaceWith(IR.string(result));
replace(rightParent, rightParent.getSecondChild().cloneTree(true));
}
}
}
return n;
}
/** Try to fold an ADD node with constant operands */
private Node tryFoldAddConstantString(Node n, Node left, Node right) {
if (left.isString() || right.isString() || left.isArrayLit() || right.isArrayLit()) {
// Add strings.
String leftString = getSideEffectFreeStringValue(left);
String rightString = getSideEffectFreeStringValue(right);
if (leftString != null && rightString != null) {
Node newStringNode = IR.string(leftString + rightString);
n.replaceWith(newStringNode);
reportChangeToEnclosingScope(newStringNode);
return newStringNode;
}
}
return n;
}
/**
* Try to fold arithmetic binary operators
*/
private Node tryFoldArithmeticOp(Node n, Node left, Node right) {
Node result = performArithmeticOp(n.getToken(), left, right);
if (result != null) {
result.useSourceInfoIfMissingFromForTree(n);
reportChangeToEnclosingScope(n);
n.replaceWith(result);
return result;
}
return n;
}
/**
* Try to fold arithmetic binary operators
*/
private Node performArithmeticOp(Token opType, Node left, Node right) {
// Unlike other operations, ADD operands are not always converted
// to Number.
if (opType == Token.ADD
&& (NodeUtil.mayBeString(left, shouldUseTypes)
|| NodeUtil.mayBeString(right, shouldUseTypes))) {
return null;
}
double result;
// TODO(johnlenz): Handle NaN with unknown value. BIT ops convert NaN
// to zero so this is a little awkward here.
Double lValObj = getSideEffectFreeNumberValue(left);
Double rValObj = getSideEffectFreeNumberValue(right);
// at least one of the two operands must have a value and both must be numeric
if ((lValObj == null && rValObj == null) || !isNumeric(left) || !isNumeric(right)) {
return null;
}
// handle the operations that have algebraic identities, since we can simplify the tree without
// actually knowing the value statically.
switch (opType) {
case ADD:
if (lValObj != null && rValObj != null) {
return maybeReplaceBinaryOpWithNumericResult(lValObj + rValObj, lValObj, rValObj);
}
if (lValObj != null && lValObj == 0) {
return right.cloneTree(true);
} else if (rValObj != null && rValObj == 0) {
return left.cloneTree(true);
}
return null;
case SUB:
if (lValObj != null && rValObj != null) {
return maybeReplaceBinaryOpWithNumericResult(lValObj - rValObj, lValObj, rValObj);
}
if (lValObj != null && lValObj == 0) {
// 0 - x -> -x
return IR.neg(right.cloneTree(true));
} else if (rValObj != null && rValObj == 0) {
// x - 0 -> x
return left.cloneTree(true);
}
return null;
case MUL:
if (lValObj != null && rValObj != null) {
return maybeReplaceBinaryOpWithNumericResult(lValObj * rValObj, lValObj, rValObj);
}
// NOTE: 0*x != 0 for all x, if x==0, then it is NaN. So we can't take advantage of that
// without some kind of non-NaN proof. So the special cases here only deal with 1*x
if (lValObj != null) {
if (lValObj == 1) {
return right.cloneTree(true);
}
} else {
if (rValObj == 1) {
return left.cloneTree(true);
}
}
return null;
case DIV:
if (lValObj != null && rValObj != null) {
if (rValObj == 0) {
return null;
}
return maybeReplaceBinaryOpWithNumericResult(lValObj / rValObj, lValObj, rValObj);
}
// NOTE: 0/x != 0 for all x, if x==0, then it is NaN
if (rValObj != null) {
if (rValObj == 1) {
// x/1->x
return left.cloneTree(true);
}
}
return null;
case EXPONENT:
if (lValObj != null && rValObj != null) {
return maybeReplaceBinaryOpWithNumericResult(
Math.pow(lValObj, rValObj), lValObj, rValObj);
}
return null;
default:
// fall-through
}
if (lValObj == null || rValObj == null) {
return null;
}
double lval = lValObj;
double rval = rValObj;
switch (opType) {
case BITAND:
result = NodeUtil.toInt32(lval) & NodeUtil.toInt32(rval);
break;
case BITOR:
result = NodeUtil.toInt32(lval) | NodeUtil.toInt32(rval);
break;
case BITXOR:
result = NodeUtil.toInt32(lval) ^ NodeUtil.toInt32(rval);
break;
case MOD:
if (rval == 0) {
return null;
}
result = lval % rval;
break;
default:
throw new Error("Unexpected arithmetic operator: " + opType);
}
return maybeReplaceBinaryOpWithNumericResult(result, lval, rval);
}
private boolean isNumeric(Node n) {
return NodeUtil.isNumericResult(n)
|| (shouldUseTypes && n.getJSType() != null && n.getJSType().isNumberValueType());
}
private Node maybeReplaceBinaryOpWithNumericResult(double result, double lval, double rval) {
// TODO(johnlenz): consider removing the result length check.
// length of the left and right value plus 1 byte for the operator.
if ((String.valueOf(result).length() <=
String.valueOf(lval).length() + String.valueOf(rval).length() + 1
// Do not try to fold arithmetic for numbers > 2^53. After that
// point, fixed-point math starts to break down and become inaccurate.
&& Math.abs(result) <= MAX_FOLD_NUMBER)
|| Double.isNaN(result)
|| result == Double.POSITIVE_INFINITY
|| result == Double.NEGATIVE_INFINITY) {
return NodeUtil.numberNode(result, null);
}
return null;
}
/**
* Expressions such as [foo() * 10 * 20] generate parse trees
* where no node has two const children ((foo() * 10) * 20), so
* performArithmeticOp() won't fold it -- tryFoldLeftChildOp() will.
* Specifically, it folds associative expressions where:
* - The left child is also an associative expression of the same time.
* - The right child is a constant NUMBER constant.
* - The left child's right child is a NUMBER constant.
*/
private Node tryFoldLeftChildOp(Node n, Node left, Node right) {
Token opType = n.getToken();
checkState((NodeUtil.isAssociative(opType) && NodeUtil.isCommutative(opType)) || n.isAdd());
checkState(!n.isAdd() || !NodeUtil.mayBeString(n, shouldUseTypes));
// Use getNumberValue to handle constants like "NaN" and "Infinity"
// other values are converted to numbers elsewhere.
Double rightValObj = getSideEffectFreeNumberValue(right);
if (rightValObj != null && left.getToken() == opType) {
checkState(left.hasTwoChildren());
Node ll = left.getFirstChild();
Node lr = ll.getNext();
Node valueToCombine = ll;
Node replacement = performArithmeticOp(opType, valueToCombine, right);
if (replacement == null) {
valueToCombine = lr;
replacement = performArithmeticOp(opType, valueToCombine, right);
}
if (replacement != null) {
// Remove the child that has been combined
left.removeChild(valueToCombine);
// Replace the left op with the remaining child.
n.replaceChild(left, left.removeFirstChild());
// New "-Infinity" node need location info explicitly
// added.
replacement.useSourceInfoIfMissingFromForTree(right);
n.replaceChild(right, replacement);
reportChangeToEnclosingScope(n);
}
}
return n;
}
private Node tryFoldAdd(Node node, Node left, Node right) {
checkArgument(node.isAdd());
if (NodeUtil.mayBeString(node, shouldUseTypes)) {
if (NodeUtil.isLiteralValue(left, false) && NodeUtil.isLiteralValue(right, false)) {
// '6' + 7
return tryFoldAddConstantString(node, left, right);
} else {
if (left.isString() && left.getString().isEmpty() && isStringTyped(right)) {
return replace(node, right.cloneTree(true));
} else if (right.isString()
&& right.getString().isEmpty()
&& isStringTyped(left)) {
return replace(node, left.cloneTree(true));
}
// a + 7 or 6 + a
return tryFoldAdjacentLiteralLeaves(node, left, right);
}
} else {
// Try arithmetic add
Node result = tryFoldArithmeticOp(node, left, right);
if (result != node) {
return result;
}
return tryFoldLeftChildOp(node, left, right);
}
}
private Node replace(Node oldNode, Node newNode) {
oldNode.replaceWith(newNode);
reportChangeToEnclosingScope(newNode);
return newNode;
}
private boolean isStringTyped(Node n) {
// We could also accept !String, but it is unlikely to be very common.
return NodeUtil.isStringResult(n)
|| (shouldUseTypes && n.getJSType() != null && n.getJSType().isStringValueType());
}
/**
* Try to fold shift operations
*/
private Node tryFoldShift(Node n, Node left, Node right) {
if (left.isNumber() &&
right.isNumber()) {
double result;
double lval = left.getDouble();
double rval = right.getDouble();
// only the lower 5 bits are used when shifting, so don't do anything
// if the shift amount is outside [0,32)
if (!(rval >= 0 && rval < 32)) {
return n;
}
int rvalInt = (int) rval;
if (rvalInt != rval) {
report(FRACTIONAL_BITWISE_OPERAND, right);
return n;
}
if (Math.floor(lval) != lval) {
report(FRACTIONAL_BITWISE_OPERAND, left);
return n;
}
int bits = jsConvertDoubleToBits(lval);
switch (n.getToken()) {
case LSH:
result = bits << rvalInt;
break;
case RSH:
result = bits >> rvalInt;
break;
case URSH:
// JavaScript always treats the result of >>> as unsigned.
// We must force Java to do the same here.
result = 0xffffffffL & (bits >>> rvalInt);
break;
default:
throw new AssertionError("Unknown shift operator: " + n.getToken());
}
Node newNumber = IR.number(result);
reportChangeToEnclosingScope(n);
n.replaceWith(newNumber);
return newNumber;
}
return n;
}
/**
* Try to fold comparison nodes, e.g ==
*/
private Node tryFoldComparison(Node n, Node left, Node right) {
TernaryValue result = evaluateComparison(this, n.getToken(), left, right);
if (result == TernaryValue.UNKNOWN) {
return n;
}
Node newNode = NodeUtil.booleanNode(result.toBoolean(true));
reportChangeToEnclosingScope(n);
n.replaceWith(newNode);
markFunctionsDeleted(n);
return newNode;
}
/** http://www.ecma-international.org/ecma-262/6.0/#sec-abstract-relational-comparison */
private static TernaryValue tryAbstractRelationalComparison(
AbstractPeepholeOptimization peepholeOptimization,
Node left,
Node right,
boolean willNegate) {
// First, try to evaluate based on the general type.
ValueType leftValueType = NodeUtil.getKnownValueType(left);
ValueType rightValueType = NodeUtil.getKnownValueType(right);
if (leftValueType != ValueType.UNDETERMINED && rightValueType != ValueType.UNDETERMINED) {
if (leftValueType == ValueType.STRING && rightValueType == ValueType.STRING) {
String lv = peepholeOptimization.getSideEffectFreeStringValue(left);
String rv = peepholeOptimization.getSideEffectFreeStringValue(right);
if (lv != null && rv != null) {
// In JS, browsers parse \v differently. So do not compare strings if one contains \v.
if (lv.indexOf('\u000B') != -1 || rv.indexOf('\u000B') != -1) {
return TernaryValue.UNKNOWN;
} else {
return TernaryValue.forBoolean(lv.compareTo(rv) < 0);
}
} else if (left.isTypeOf()
&& right.isTypeOf()
&& left.getFirstChild().isName()
&& right.getFirstChild().isName()
&& left.getFirstChild().getString().equals(right.getFirstChild().getString())) {
// Special case: `typeof a < typeof a` is always false.
return TernaryValue.FALSE;
}
}
}
// Then, try to evaluate based on the value of the node. Try comparing as numbers.
Double lv = peepholeOptimization.getSideEffectFreeNumberValue(left);
Double rv = peepholeOptimization.getSideEffectFreeNumberValue(right);
if (lv == null || rv == null) {
// Special case: `x < x` is always false.
//
// TODO(moz): If we knew the named value wouldn't be NaN, it would be nice to handle
// LE and GE. We should use type information if available here.
if (!willNegate && left.isName() && right.isName()) {
if (left.getString().equals(right.getString())) {
return TernaryValue.FALSE;
}
}
return TernaryValue.UNKNOWN;
}
if (Double.isNaN(lv) || Double.isNaN(rv)) {
return TernaryValue.forBoolean(willNegate);
} else {
return TernaryValue.forBoolean(lv.doubleValue() < rv.doubleValue());
}
}
/** http://www.ecma-international.org/ecma-262/6.0/#sec-abstract-equality-comparison */
private static TernaryValue tryAbstractEqualityComparison(
AbstractPeepholeOptimization peepholeOptimization, Node left, Node right) {
// Evaluate based on the general type.
ValueType leftValueType = NodeUtil.getKnownValueType(left);
ValueType rightValueType = NodeUtil.getKnownValueType(right);
if (leftValueType != ValueType.UNDETERMINED && rightValueType != ValueType.UNDETERMINED) {
// Delegate to strict equality comparison for values of the same type.
if (leftValueType == rightValueType) {
return tryStrictEqualityComparison(peepholeOptimization, left, right);
}
if ((leftValueType == ValueType.NULL && rightValueType == ValueType.VOID)
|| (leftValueType == ValueType.VOID && rightValueType == ValueType.NULL)) {
return TernaryValue.TRUE;
}
if ((leftValueType == ValueType.NUMBER && rightValueType == ValueType.STRING)
|| rightValueType == ValueType.BOOLEAN) {
Double rv = peepholeOptimization.getSideEffectFreeNumberValue(right);
return rv == null
? TernaryValue.UNKNOWN
: tryAbstractEqualityComparison(peepholeOptimization, left, IR.number(rv));
}
if ((leftValueType == ValueType.STRING && rightValueType == ValueType.NUMBER)
|| leftValueType == ValueType.BOOLEAN) {
Double lv = peepholeOptimization.getSideEffectFreeNumberValue(left);
return lv == null
? TernaryValue.UNKNOWN
: tryAbstractEqualityComparison(peepholeOptimization, IR.number(lv), right);
}
if ((leftValueType == ValueType.STRING || leftValueType == ValueType.NUMBER)
&& rightValueType == ValueType.OBJECT) {
return TernaryValue.UNKNOWN;
}
if (leftValueType == ValueType.OBJECT
&& (rightValueType == ValueType.STRING || rightValueType == ValueType.NUMBER)) {
return TernaryValue.UNKNOWN;
}
return TernaryValue.FALSE;
}
// In general, the rest of the cases cannot be folded.
return TernaryValue.UNKNOWN;
}
/** http://www.ecma-international.org/ecma-262/6.0/#sec-strict-equality-comparison */
private static TernaryValue tryStrictEqualityComparison(
AbstractPeepholeOptimization peepholeOptimization, Node left, Node right) {
// First, try to evaluate based on the general type.
ValueType leftValueType = NodeUtil.getKnownValueType(left);
ValueType rightValueType = NodeUtil.getKnownValueType(right);
if (leftValueType != ValueType.UNDETERMINED && rightValueType != ValueType.UNDETERMINED) {
// Strict equality can only be true for values of the same type.
if (leftValueType != rightValueType) {
return TernaryValue.FALSE;
}
switch (leftValueType) {
case VOID:
case NULL:
return TernaryValue.TRUE;
case NUMBER:
{
if (NodeUtil.isNaN(left)) {
return TernaryValue.FALSE;
}
if (NodeUtil.isNaN(right)) {
return TernaryValue.FALSE;
}
Double lv = peepholeOptimization.getSideEffectFreeNumberValue(left);
Double rv = peepholeOptimization.getSideEffectFreeNumberValue(right);
if (lv != null && rv != null) {
return TernaryValue.forBoolean(lv.doubleValue() == rv.doubleValue());
}
break;
}
case STRING:
{
String lv = peepholeOptimization.getSideEffectFreeStringValue(left);
String rv = peepholeOptimization.getSideEffectFreeStringValue(right);
if (lv != null && rv != null) {
// In JS, browsers parse \v differently. So do not consider strings
// equal if one contains \v.
if (lv.indexOf('\u000B') != -1 || rv.indexOf('\u000B') != -1) {
return TernaryValue.UNKNOWN;
} else {
return lv.equals(rv) ? TernaryValue.TRUE : TernaryValue.FALSE;
}
} else if (left.isTypeOf()
&& right.isTypeOf()
&& left.getFirstChild().isName()
&& right.getFirstChild().isName()
&& left.getFirstChild().getString().equals(right.getFirstChild().getString())) {
// Special case, typeof a == typeof a is always true.
return TernaryValue.TRUE;
}
break;
}
case BOOLEAN:
{
TernaryValue lv = peepholeOptimization.getSideEffectFreeBooleanValue(left);
TernaryValue rv = peepholeOptimization.getSideEffectFreeBooleanValue(right);
return lv.and(rv).or(lv.not().and(rv.not()));
}
default: // Symbol and Object cannot be folded in the general case.
return TernaryValue.UNKNOWN;
}
}
// Then, try to evaluate based on the value of the node. There's only one special case:
// Any strict equality comparison against NaN returns false.
if (NodeUtil.isNaN(left) || NodeUtil.isNaN(right)) {
return TernaryValue.FALSE;
}
return TernaryValue.UNKNOWN;
}
static TernaryValue evaluateComparison(
AbstractPeepholeOptimization peepholeOptimization, Token op, Node left, Node right) {
// Don't try to minimize side-effects here.
if (peepholeOptimization.mayHaveSideEffects(left)
|| peepholeOptimization.mayHaveSideEffects(right)) {
return TernaryValue.UNKNOWN;
}
switch (op) {
case EQ:
return tryAbstractEqualityComparison(peepholeOptimization, left, right);
case NE:
return tryAbstractEqualityComparison(peepholeOptimization, left, right).not();
case SHEQ:
return tryStrictEqualityComparison(peepholeOptimization, left, right);
case SHNE:
return tryStrictEqualityComparison(peepholeOptimization, left, right).not();
case LT:
return tryAbstractRelationalComparison(peepholeOptimization, left, right, false);
case GT:
return tryAbstractRelationalComparison(peepholeOptimization, right, left, false);
case LE:
return tryAbstractRelationalComparison(peepholeOptimization, right, left, true).not();
case GE:
return tryAbstractRelationalComparison(peepholeOptimization, left, right, true).not();
default:
break;
}
throw new IllegalStateException("Unexpected operator for comparison");
}
/**
* Try to fold away unnecessary object instantiation.
* e.g. this[new String('eval')] -> this.eval
*/
private Node tryFoldCtorCall(Node n) {
checkArgument(n.isNew());
// we can remove this for GETELEM calls (anywhere else?)
if (inForcedStringContext(n)) {
return tryFoldInForcedStringContext(n);
}
return n;
}
/**
* Remove useless calls:
* Object.defineProperties(o, {}) -> o
*/
private Node tryFoldCall(Node n) {
checkArgument(n.isCall());
if (NodeUtil.isObjectDefinePropertiesDefinition(n)) {
Node srcObj = n.getLastChild();
if (srcObj.isObjectLit() && !srcObj.hasChildren()) {
Node parent = n.getParent();
Node destObj = n.getSecondChild().detach();
parent.replaceChild(n, destObj);
reportChangeToEnclosingScope(parent);
}
}
return n;
}
/** Returns whether this node must be coerced to a string. */
private static boolean inForcedStringContext(Node n) {
if (n.getParent().isGetElem()
&& n.getParent().getLastChild() == n) {
return true;
}
// we can fold in the case "" + new String("")
return n.getParent().isAdd();
}
private Node tryFoldInForcedStringContext(Node n) {
// For now, we only know how to fold ctors.
checkArgument(n.isNew());
Node objectType = n.getFirstChild();
if (!objectType.isName()) {
return n;
}
if (objectType.getString().equals("String")) {
Node value = objectType.getNext();
String stringValue = null;
if (value == null) {
stringValue = "";
} else {
stringValue = getSideEffectFreeStringValue(value);
}
if (stringValue == null) {
return n;
}
Node parent = n.getParent();
Node newString = IR.string(stringValue);
parent.replaceChild(n, newString);
newString.useSourceInfoIfMissingFrom(parent);
reportChangeToEnclosingScope(parent);
return newString;
}
return n;
}
/**
* Try to fold array-element. e.g [1, 2, 3][10];
*/
private Node tryFoldGetElem(Node n, Node left, Node right) {
checkArgument(n.isGetElem());
if (left.isObjectLit()) {
return tryFoldObjectPropAccess(n, left, right);
}
if (left.isArrayLit()) {
return tryFoldArrayAccess(n, left, right);
}
if (left.isString()) {
return tryFoldStringArrayAccess(n, left, right);
}
return n;
}
/**
* Try to fold array-length. e.g [1, 2, 3].length ==> 3, [x, y].length ==> 2
*/
private Node tryFoldGetProp(Node n, Node left, Node right) {
checkArgument(n.isGetProp());
if (left.isObjectLit()) {
return tryFoldObjectPropAccess(n, left, right);
}
if (right.isString() &&
right.getString().equals("length")) {
int knownLength = -1;
switch (left.getToken()) {
case ARRAYLIT:
if (mayHaveSideEffects(left)) {
// Nope, can't fold this, without handling the side-effects.
return n;
}
knownLength = left.getChildCount();
break;
case STRING:
knownLength = left.getString().length();
break;
default:
// Not a foldable case, forget it.
return n;
}
checkState(knownLength != -1);
Node lengthNode = IR.number(knownLength);
reportChangeToEnclosingScope(n);
n.replaceWith(lengthNode);
return lengthNode;
}
return n;
}
private Node tryFoldArrayAccess(Node n, Node left, Node right) {
// If GETPROP/GETELEM is used as assignment target the array literal is
// acting as a temporary we can't fold it here:
// "[][0] += 1"
if (NodeUtil.isLValue(n)) {
return n;
}
if (!right.isNumber()) {
// Sometimes people like to use complex expressions to index into
// arrays, or strings to index into array methods.
return n;
}
double index = right.getDouble();
int intIndex = (int) index;
if (intIndex != index) {
report(INVALID_GETELEM_INDEX_ERROR, right);
return n;
}
Node current = intIndex >= 0 ? left.getFirstChild() : null;
Node elem = null;
for (int i = 0; current != null; i++) {
if (current.isSpread()) {
// The only time we can fold getelems with spread is for spread arrays literals, and
// `tryFlattenArray` already flattens those.
return n;
}
if (i != intIndex) {
if (mayHaveSideEffects(current)) {
return n;
}
} else {
elem = current;
}
current = current.getNext();
}
if (elem == null) { // If the index was out of bounds
elem = NodeUtil.newUndefinedNode(left);
} else if (elem.isEmpty()) {
elem = NodeUtil.newUndefinedNode(elem);
} else {
left.removeChild(elem);
}
// Replace the entire GETELEM with the value
n.replaceWith(elem);
reportChangeToEnclosingScope(elem);
return elem;
}
/**
* Flattens array- or object-literals that contain spreads of other literals.
*
* Does not recurse into nested spreads because this method is already called as part of a
* postorder traversal and nested spreads will already have been flattened.
*
*
Example: `[0, ...[1, 2, 3], 4, ...[5]]` => `[0, 1, 2, 3, 4, 5]`
*/
private Node tryFlattenArrayOrObjectLit(Node parentLit) {
for (Node child = parentLit.getFirstChild(); child != null; ) {
// We have to store the next element here because nodes may be inserted below.
Node spread = child;
child = child.getNext();
if (!spread.isSpread()) {
continue;
}
Node innerLit = spread.getOnlyChild();
if (!parentLit.getToken().equals(innerLit.getToken())) {
continue; // We only want to inline arrays into arrays and objects into objects.
}
parentLit.addChildrenAfter(innerLit.removeChildren(), spread);
spread.detach();
reportChangeToEnclosingScope(parentLit);
}
return parentLit;
}
private Node tryFoldStringArrayAccess(Node n, Node left, Node right) {
// If GETPROP/GETELEM is used as assignment target the array literal is
// acting as a temporary we can't fold it here:
// "[][0] += 1"
if (NodeUtil.isLValue(n)) {
return n;
}
if (!right.isNumber()) {
// Sometimes people like to use complex expressions to index into
// arrays, or strings to index into array methods.
return n;
}
double index = right.getDouble();
int intIndex = (int) index;
if (intIndex != index) {
report(INVALID_GETELEM_INDEX_ERROR, right);
return n;
}
checkState(left.isString());
String value = left.getString();
if (intIndex < 0 || intIndex >= value.length()) {
Node undefined = NodeUtil.newUndefinedNode(left);
n.replaceWith(undefined);
reportChangeToEnclosingScope(undefined);
return undefined;
}
char c = 0;
// Note: For now skip the strings with unicode
// characters as I don't understand the differences
// between Java and JavaScript.
for (int i = 0; i <= intIndex; i++) {
c = value.charAt(i);
if (c < 32 || c > 127) {
return n;
}
}
Node elem = IR.string(Character.toString(c));
// Replace the entire GETELEM with the value
n.replaceWith(elem);
reportChangeToEnclosingScope(elem);
return elem;
}
private Node tryFoldObjectPropAccess(Node n, Node left, Node right) {
checkArgument(NodeUtil.isGet(n));
if (!left.isObjectLit() || !right.isString()) {
return n;
}
if (NodeUtil.isLValue(n)) {
// If GETPROP/GETELEM is used as assignment target the object literal is
// acting as a temporary we can't fold it here:
// "{a:x}.a += 1" is not "x += 1"
return n;
}
// find the last definition in the object literal
Node key = null;
Node value = null;
for (Node c = left.getFirstChild(); c != null; c = c.getNext()) {
switch (c.getToken()) {
case SETTER_DEF:
break;
case OBJECT_SPREAD:
// Reset the search because spread could overwrite any previous result.
key = null;
value = null;
break;
case COMPUTED_PROP:
// don't handle computed properties unless the input is a simple string
Node prop = c.getFirstChild();
if (!prop.isString()) {
return n;
}
if (prop.getString().equals(right.getString())) {
key = c;
value = c.getSecondChild();
}
break;
case GETTER_DEF:
case STRING_KEY:
case MEMBER_FUNCTION_DEF:
if (c.getString().equals(right.getString())) {
key = c;
value = key.getFirstChild();
}
break;
default:
throw new IllegalStateException();
}
}
// Didn't find a definition of the name in the object literal, it might
// be coming from the Object prototype
if (value == null) {
return n;
}
/** `super` captures a hidden reference to the declaring objectlit, so we can't fold it away. */
if (NodeUtil.referencesSuper(value)) {
return n;
}
/**
* Check to see if there are any side-effects to this object-literal.
*
*
We remove the value we're going to use because its side-effects will be preserved.
*/
Node tempValue = IR.nullNode();
value.replaceWith(tempValue);
boolean hasSideEffectBesidesValue = mayHaveSideEffects(left);
tempValue.replaceWith(value);
if (hasSideEffectBesidesValue) {
return n;
}
boolean keyIsGetter = NodeUtil.isGetOrSetKey(key);
boolean nIsInvoked = NodeUtil.isInvocationTarget(n);
if (keyIsGetter || nIsInvoked) {
// When the code looks like:
// {x: f}.x();
// {get x() {...}}.x;
// {get ['x']() {...}}.x;
/**
* It's not safe, in general, to convert that to just a function call, because the receiver
* value will be wrong.
*
*
However, there are some cases where it's ok which we check here.
*/
if (!value.isFunction() || NodeUtil.referencesOwnReceiver(value)) {
return n;
}
}
value.detach();
if (keyIsGetter) {
value = IR.call(value);
value.putBooleanProp(Node.FREE_CALL, true);
} else if (nIsInvoked) {
n.getParent().putBooleanProp(Node.FREE_CALL, true);
}
n.replaceWith(value);
reportChangeToEnclosingScope(value);
markFunctionsDeleted(n);
return n;
}
}