/*
* Copyright 2010 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 com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.javascript.jscomp.MinimizedCondition.MinimizationStyle;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import com.google.javascript.rhino.TypeI;
import com.google.javascript.rhino.jstype.TernaryValue;
/**
* A peephole optimization that minimizes conditional expressions
* according to De Morgan's laws.
* Also rewrites conditional statements as expressions by replacing them
* with HOOKs and short-circuit binary operators.
*
* Based on PeepholeSubstituteAlternateSyntax
*/
class PeepholeMinimizeConditions
extends AbstractPeepholeOptimization {
private static final int AND_PRECEDENCE = NodeUtil.precedence(Token.AND);
private final boolean late;
private final boolean useTypes;
/**
* @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 (such as using string splitting,
* merging statements with commas, etc). When this is true, we would
* do anything to minimize for size.
*/
PeepholeMinimizeConditions(boolean late, boolean useTypes) {
this.late = late;
this.useTypes = useTypes;
}
/**
* Tries to apply our various peephole minimizations on the passed in node.
*/
@Override
@SuppressWarnings("fallthrough")
public Node optimizeSubtree(Node node) {
switch (node.getToken()) {
case THROW:
case RETURN: {
Node result = tryRemoveRedundantExit(node);
if (result != node) {
return result;
}
return tryReplaceExitWithBreak(node);
}
// TODO(johnlenz): Maybe remove redundant BREAK and CONTINUE. Overlaps
// with MinimizeExitPoints.
case NOT:
tryMinimizeCondition(node.getFirstChild());
return tryMinimizeNot(node);
case IF:
performCoercionSubstitutions(node.getFirstChild());
performConditionSubstitutions(node.getFirstChild());
return tryMinimizeIf(node);
case EXPR_RESULT:
performCoercionSubstitutions(node.getFirstChild());
performConditionSubstitutions(node.getFirstChild());
return tryMinimizeExprResult(node);
case HOOK:
performCoercionSubstitutions(node.getFirstChild());
performConditionSubstitutions(node.getFirstChild());
return tryMinimizeHook(node);
case WHILE:
case DO:
tryMinimizeCondition(NodeUtil.getConditionExpression(node));
return node;
case FOR:
tryJoinForCondition(node);
tryMinimizeCondition(NodeUtil.getConditionExpression(node));
return node;
case BLOCK:
return tryReplaceIf(node);
case EQ:
case NE:
case SHEQ:
case SHNE:
return tryReplaceComparisonWithCoercion(node, true /* booleanResult */);
default:
return node; //Nothing changed
}
}
private void tryJoinForCondition(Node n) {
if (!late) {
return;
}
Node block = n.getLastChild();
Node maybeIf = block.getFirstChild();
if (maybeIf != null && maybeIf.isIf()) {
Node thenBlock = maybeIf.getSecondChild();
Node maybeBreak = thenBlock.getFirstChild();
if (maybeBreak != null && maybeBreak.isBreak()
&& !maybeBreak.hasChildren()) {
// Preserve the IF ELSE expression is there is one.
if (maybeIf.getChildCount() == 3) {
block.replaceChild(maybeIf,
maybeIf.getLastChild().detach());
} else {
NodeUtil.redeclareVarsInsideBranch(thenBlock);
block.removeFirstChild();
}
Node ifCondition = maybeIf.removeFirstChild();
Node fixedIfCondition = IR.not(ifCondition)
.srcref(ifCondition);
// OK, join the IF expression with the FOR expression
Node forCondition = NodeUtil.getConditionExpression(n);
if (forCondition.isEmpty()) {
n.replaceChild(forCondition, fixedIfCondition);
} else {
Node replacement = new Node(Token.AND);
n.replaceChild(forCondition, replacement);
replacement.addChildToBack(forCondition);
replacement.addChildToBack(fixedIfCondition);
}
reportCodeChange();
}
}
}
/**
* Use "return x?1:2;" in place of "if(x)return 1;return 2;"
*/
private Node tryReplaceIf(Node n) {
Node next = null;
for (Node child = n.getFirstChild();
child != null; child = next){
next = child.getNext();
if (child.isIf()){
Node cond = child.getFirstChild();
Node thenBranch = cond.getNext();
Node elseBranch = thenBranch.getNext();
Node nextNode = child.getNext();
if (nextNode != null && elseBranch == null
&& isReturnBlock(thenBranch)
&& nextNode.isIf()) {
Node nextCond = nextNode.getFirstChild();
Node nextThen = nextCond.getNext();
Node nextElse = nextThen.getNext();
if (thenBranch.isEquivalentToTyped(nextThen)) {
// Transform
// if (x) return 1; if (y) return 1;
// to
// if (x||y) return 1;
child.detach();
child.detachChildren();
Node newCond = new Node(Token.OR, cond);
nextNode.replaceChild(nextCond, newCond);
newCond.addChildToBack(nextCond);
reportCodeChange();
} else if (nextElse != null
&& thenBranch.isEquivalentToTyped(nextElse)) {
// Transform
// if (x) return 1; if (y) foo() else return 1;
// to
// if (!x&&y) foo() else return 1;
child.detach();
child.detachChildren();
Node newCond = new Node(Token.AND,
IR.not(cond).srcref(cond));
nextNode.replaceChild(nextCond, newCond);
newCond.addChildToBack(nextCond);
reportCodeChange();
}
} else if (nextNode != null && elseBranch == null &&
isReturnBlock(thenBranch) && isReturnExpression(nextNode)) {
Node thenExpr = null;
// if(x)return; return 1 -> return x?void 0:1
if (isReturnExpressBlock(thenBranch)) {
thenExpr = getBlockReturnExpression(thenBranch);
thenExpr.detach();
} else {
thenExpr = NodeUtil.newUndefinedNode(child);
}
Node elseExpr = nextNode.getFirstChild();
cond.detach();
elseExpr.detach();
Node returnNode = IR.returnNode(
IR.hook(cond, thenExpr, elseExpr)
.srcref(child));
n.replaceChild(child, returnNode);
n.removeChild(nextNode);
reportCodeChange();
// everything else in the block is dead code.
break;
} else if (elseBranch != null && statementMustExitParent(thenBranch)) {
child.removeChild(elseBranch);
n.addChildAfter(elseBranch, child);
reportCodeChange();
}
}
}
return n;
}
private static boolean statementMustExitParent(Node n) {
switch (n.getToken()) {
case THROW:
case RETURN:
return true;
case BLOCK:
if (n.hasChildren()) {
Node child = n.getLastChild();
return statementMustExitParent(child);
}
return false;
// TODO(johnlenz): handle TRY/FINALLY
case FUNCTION:
default:
return false;
}
}
/**
* Replace duplicate exits in control structures. If the node following
* the exit node expression has the same effect as exit node, the node can
* be replaced or removed.
* For example:
* "while (a) {return f()} return f();" ==> "while (a) {break} return f();"
* "while (a) {throw 'ow'} throw 'ow';" ==> "while (a) {break} throw 'ow';"
*
* @param n An follow control exit expression (a THROW or RETURN node)
* @return The replacement for n, or the original if no change was made.
*/
private Node tryReplaceExitWithBreak(Node n) {
Node result = n.getFirstChild();
// Find the enclosing control structure, if any, that a "break" would exit
// from.
Node breakTarget = n;
for (; !ControlFlowAnalysis.isBreakTarget(breakTarget, null /* no label */);
breakTarget = breakTarget.getParent()) {
if (breakTarget.isFunction() || breakTarget.isScript()) {
// No break target.
return n;
}
}
Node follow = ControlFlowAnalysis.computeFollowNode(breakTarget);
// Skip pass all the finally blocks because both the break and return will
// also trigger all the finally blocks. However, the order of execution is
// slightly changed. Consider:
//
// return a() -> finally { b() } -> return a()
//
// which would call a() first. However, changing the first return to a
// break will result in calling b().
Node prefinallyFollows = follow;
follow = skipFinallyNodes(follow);
if (prefinallyFollows != follow) {
// There were finally clauses
if (!isPure(result)) {
// Can't defer the exit
return n;
}
}
if (follow == null && (n.isThrow() || result != null)) {
// Can't complete remove a throw here or a return with a result.
return n;
}
// When follow is null, this mean the follow of a break target is the
// end of a function. This means a break is same as return.
if (follow == null || areMatchingExits(n, follow)) {
Node replacement = IR.breakNode();
n.replaceWith(replacement);
this.reportCodeChange();
return replacement;
}
return n;
}
/**
* Remove duplicate exits. If the node following the exit node expression
* has the same effect as exit node, the node can be removed.
* For example:
* "if (a) {return f()} return f();" ==> "if (a) {} return f();"
* "if (a) {throw 'ow'} throw 'ow';" ==> "if (a) {} throw 'ow';"
*
* @param n An follow control exit expression (a THROW or RETURN node)
* @return The replacement for n, or the original if no change was made.
*/
private Node tryRemoveRedundantExit(Node n) {
Node exitExpr = n.getFirstChild();
Node follow = ControlFlowAnalysis.computeFollowNode(n);
// Skip pass all the finally blocks because both the fall through and return
// will also trigger all the finally blocks.
Node prefinallyFollows = follow;
follow = skipFinallyNodes(follow);
if (prefinallyFollows != follow) {
// There were finally clauses
if (!isPure(exitExpr)) {
// Can't replace the return
return n;
}
}
if (follow == null && (n.isThrow() || exitExpr != null)) {
// Can't complete remove a throw here or a return with a result.
return n;
}
// When follow is null, this mean the follow of a break target is the
// end of a function. This means a break is same as return.
if (follow == null || areMatchingExits(n, follow)) {
n.detach();
reportCodeChange();
return null;
}
return n;
}
/**
* @return Whether the expression does not produces and can not be affected
* by side-effects.
*/
boolean isPure(Node n) {
return n == null
|| (!NodeUtil.canBeSideEffected(n)
&& !mayHaveSideEffects(n));
}
/**
* @return n or the node following any following finally nodes.
*/
static Node skipFinallyNodes(Node n) {
while (n != null && NodeUtil.isTryFinallyNode(n.getParent(), n)) {
n = ControlFlowAnalysis.computeFollowNode(n);
}
return n;
}
/**
* Check whether one exit can be replaced with another. Verify:
* 1) They are identical expressions
* 2) If an exception is possible that the statements, the original
* and the potential replacement are in the same exception handler.
*/
boolean areMatchingExits(Node nodeThis, Node nodeThat) {
return nodeThis.isEquivalentTo(nodeThat)
&& (!isExceptionPossible(nodeThis)
|| getExceptionHandler(nodeThis) == getExceptionHandler(nodeThat));
}
static boolean isExceptionPossible(Node n) {
// TODO(johnlenz): maybe use ControlFlowAnalysis.mayThrowException?
Preconditions.checkState(n.isReturn() || n.isThrow(), n);
return n.isThrow()
|| (n.hasChildren()
&& !NodeUtil.isLiteralValue(n.getLastChild(), true));
}
static Node getExceptionHandler(Node n) {
return ControlFlowAnalysis.getExceptionHandler(n);
}
/**
* Try to minimize NOT nodes such as !(x==y).
*
* Returns the replacement for n or the original if no change was made
*/
private Node tryMinimizeNot(Node n) {
Preconditions.checkArgument(n.isNot());
Node parent = n.getParent();
Node notChild = n.getFirstChild();
// negative operator of the current one : == -> != for instance.
Token complementOperator;
switch (notChild.getToken()) {
case EQ:
complementOperator = Token.NE;
break;
case NE:
complementOperator = Token.EQ;
break;
case SHEQ:
complementOperator = Token.SHNE;
break;
case SHNE:
complementOperator = Token.SHEQ;
break;
// GT, GE, LT, LE are not handled in this because !(x<NaN) != x>=NaN.
default:
return n;
}
Node newOperator = n.removeFirstChild();
newOperator.setToken(complementOperator);
parent.replaceChild(n, newOperator);
reportCodeChange();
return newOperator;
}
/**
* Try to remove leading NOTs from EXPR_RESULTS.
*
* Returns the replacement for n or the original if no replacement was
* necessary.
*/
private Node tryMinimizeExprResult(Node n) {
MinimizedCondition minCond =
MinimizedCondition.fromConditionNode(n.getFirstChild());
MinimizedCondition.MeasuredNode mNode =
minCond.getMinimized(MinimizationStyle.ALLOW_LEADING_NOT);
Node placeholder = minCond.getPlaceholder();
if (mNode.getNode().isNot()) {
// Remove the leading NOT in the EXPR_RESULT.
n.replaceChild(placeholder, mNode.getNode().removeFirstChild());
reportCodeChange();
} else {
replaceNode(placeholder, mNode);
}
return n;
}
/**
* Try flipping HOOKs that have negated conditions.
*
* Returns the replacement for n or the original if no replacement was
* necessary.
*/
private Node tryMinimizeHook(Node n) {
MinimizedCondition minCond =
MinimizedCondition.fromConditionNode(n.getFirstChild());
MinimizedCondition.MeasuredNode mNode =
minCond.getMinimized(MinimizationStyle.ALLOW_LEADING_NOT);
Node placeholder = minCond.getPlaceholder();
if (mNode.getNode().isNot()) {
// Swap the HOOK
Node thenBranch = n.getSecondChild();
n.replaceChild(placeholder, mNode.getNode().removeFirstChild());
n.removeChild(thenBranch);
n.addChildToBack(thenBranch);
reportCodeChange();
} else {
replaceNode(placeholder, mNode);
}
return n;
}
/**
* Try turning IF nodes into smaller HOOKs
*
* Returns the replacement for n or the original if no replacement was
* necessary.
*/
private Node tryMinimizeIf(Node n) {
Node parent = n.getParent();
Node originalCond = n.getFirstChild();
/* If the condition is a literal, we'll let other
* optimizations try to remove useless code.
*/
if (NodeUtil.isLiteralValue(originalCond, true)) {
return n;
}
Node thenBranch = originalCond.getNext();
Node elseBranch = thenBranch.getNext();
MinimizedCondition minCond =
MinimizedCondition.fromConditionNode(originalCond);
originalCond = null; // originalCond was mutated and should not be used.
Node placeholder = minCond.getPlaceholder();
MinimizedCondition.MeasuredNode unnegatedCond;
MinimizedCondition.MeasuredNode shortCond;
// Compute two minimized representations. The first representation counts
// a leading NOT node, and the second ignores a leading NOT node.
// If we can fold the if statement into a HOOK or boolean operation,
// then the NOT node does not matter, and we prefer the second condition.
// If we cannot fold the if statement, then we prefer the first condition.
unnegatedCond = minCond.getMinimized(MinimizationStyle.PREFER_UNNEGATED);
shortCond = minCond.getMinimized(MinimizationStyle.ALLOW_LEADING_NOT);
if (elseBranch == null) {
if (isFoldableExpressBlock(thenBranch)) {
Node expr = getBlockExpression(thenBranch);
if (!late && isPropertyAssignmentInExpression(expr)) {
// Keep opportunities for CollapseProperties such as
// a.longIdentifier || a.longIdentifier = ... -> var a = ...;
// until CollapseProperties has been run.
replaceNode(placeholder, unnegatedCond);
return n;
}
if (shortCond.getNode().isNot()) {
// if(!x)bar(); -> x||bar();
Node or = IR.or(
shortCond.getNode().removeFirstChild(),
expr.removeFirstChild()).srcref(n);
Node newExpr = NodeUtil.newExpr(or);
parent.replaceChild(n, newExpr);
reportCodeChange();
return newExpr;
}
// True, but removed for performance reasons.
// Preconditions.checkState(shortCond.isEquivalentTo(unnegatedCond));
// if(x)foo(); -> x&&foo();
if (isLowerPrecedence(shortCond.getNode(), AND_PRECEDENCE) &&
isLowerPrecedence(expr.getFirstChild(),
AND_PRECEDENCE)) {
// One additional set of parentheses is worth the change even if
// there is no immediate code size win. However, two extra pair of
// {}, we would have to think twice. (unless we know for sure the
// we can further optimize its parent.
replaceNode(placeholder, shortCond);
return n;
}
n.removeChild(placeholder);
Node and = IR.and(shortCond.getNode(), expr.removeFirstChild()).srcref(n);
Node newExpr = NodeUtil.newExpr(and);
parent.replaceChild(n, newExpr);
reportCodeChange();
return newExpr;
} else {
// Try to combine two IF-ELSE
if (NodeUtil.isStatementBlock(thenBranch) &&
thenBranch.hasOneChild()) {
Node innerIf = thenBranch.getFirstChild();
if (innerIf.isIf()) {
Node innerCond = innerIf.getFirstChild();
Node innerThenBranch = innerCond.getNext();
Node innerElseBranch = innerThenBranch.getNext();
if (innerElseBranch == null &&
!(isLowerPrecedence(unnegatedCond.getNode(), AND_PRECEDENCE) &&
isLowerPrecedence(innerCond, AND_PRECEDENCE))) {
n.detachChildren();
n.addChildToBack(
IR.and(
unnegatedCond.getNode(),
innerCond.detach())
.srcref(placeholder));
n.addChildToBack(innerThenBranch.detach());
reportCodeChange();
// Not worth trying to fold the current IF-ELSE into && because
// the inner IF-ELSE wasn't able to be folded into && anyways.
return n;
}
}
}
}
replaceNode(placeholder, unnegatedCond);
return n;
}
/* TODO(dcc) This modifies the siblings of n, which is undesirable for a
* peephole optimization. This should probably get moved to another pass.
*/
tryRemoveRepeatedStatements(n);
// if(!x)foo();else bar(); -> if(x)bar();else foo();
// An additional set of curly braces isn't worth it.
if (shortCond.getNode().isNot() && !consumesDanglingElse(elseBranch)) {
n.replaceChild(placeholder, shortCond.getNode().removeFirstChild());
n.removeChild(thenBranch);
n.addChildToBack(thenBranch);
reportCodeChange();
return n;
}
// if(x)return 1;else return 2; -> return x?1:2;
if (isReturnExpressBlock(thenBranch) && isReturnExpressBlock(elseBranch)) {
Node thenExpr = getBlockReturnExpression(thenBranch);
Node elseExpr = getBlockReturnExpression(elseBranch);
n.removeChild(placeholder);
thenExpr.detach();
elseExpr.detach();
// note - we ignore any cases with "return;", technically this
// can be converted to "return undefined;" or some variant, but
// that does not help code size.
Node returnNode = IR.returnNode(
IR.hook(shortCond.getNode(), thenExpr, elseExpr)
.srcref(n));
parent.replaceChild(n, returnNode);
reportCodeChange();
return returnNode;
}
boolean thenBranchIsExpressionBlock = isFoldableExpressBlock(thenBranch);
boolean elseBranchIsExpressionBlock = isFoldableExpressBlock(elseBranch);
if (thenBranchIsExpressionBlock && elseBranchIsExpressionBlock) {
Node thenOp = getBlockExpression(thenBranch).getFirstChild();
Node elseOp = getBlockExpression(elseBranch).getFirstChild();
if (thenOp.getToken() == elseOp.getToken()) {
// if(x)a=1;else a=2; -> a=x?1:2;
if (NodeUtil.isAssignmentOp(thenOp)) {
Node lhs = thenOp.getFirstChild();
if (areNodesEqualForInlining(lhs, elseOp.getFirstChild()) &&
// if LHS has side effects, don't proceed [since the optimization
// evaluates LHS before cond]
// NOTE - there are some circumstances where we can
// proceed even if there are side effects...
!mayEffectMutableState(lhs) &&
(!mayHaveSideEffects(unnegatedCond.getNode()) ||
(thenOp.isAssign() && thenOp.getFirstChild().isName()))) {
n.removeChild(placeholder);
Node assignName = thenOp.removeFirstChild();
Node thenExpr = thenOp.removeFirstChild();
Node elseExpr = elseOp.getLastChild();
elseOp.removeChild(elseExpr);
Node hookNode = IR.hook(shortCond.getNode(), thenExpr, elseExpr)
.srcref(n);
Node assign = new Node(thenOp.getToken(), assignName, hookNode).srcref(thenOp);
Node expr = NodeUtil.newExpr(assign);
parent.replaceChild(n, expr);
reportCodeChange();
return expr;
}
}
}
// if(x)foo();else bar(); -> x?foo():bar()
n.removeChild(placeholder);
thenOp.detach();
elseOp.detach();
Node expr = IR.exprResult(
IR.hook(shortCond.getNode(), thenOp, elseOp).srcref(n));
parent.replaceChild(n, expr);
reportCodeChange();
return expr;
}
boolean thenBranchIsVar = isVarBlock(thenBranch);
boolean elseBranchIsVar = isVarBlock(elseBranch);
// if(x)var y=1;else y=2 -> var y=x?1:2
if (thenBranchIsVar && elseBranchIsExpressionBlock &&
getBlockExpression(elseBranch).getFirstChild().isAssign()) {
Node var = getBlockVar(thenBranch);
Node elseAssign = getBlockExpression(elseBranch).getFirstChild();
Node name1 = var.getFirstChild();
Node maybeName2 = elseAssign.getFirstChild();
if (name1.hasChildren()
&& maybeName2.isName()
&& name1.getString().equals(maybeName2.getString())) {
Preconditions.checkState(name1.hasOneChild());
Node thenExpr = name1.removeFirstChild();
Node elseExpr = elseAssign.getLastChild().detach();
placeholder.detach();
Node hookNode = IR.hook(shortCond.getNode(), thenExpr, elseExpr)
.srcref(n);
var.detach();
name1.addChildToBack(hookNode);
parent.replaceChild(n, var);
reportCodeChange();
return var;
}
// if(x)y=1;else var y=2 -> var y=x?1:2
} else if (elseBranchIsVar && thenBranchIsExpressionBlock &&
getBlockExpression(thenBranch).getFirstChild().isAssign()) {
Node var = getBlockVar(elseBranch);
Node thenAssign = getBlockExpression(thenBranch).getFirstChild();
Node maybeName1 = thenAssign.getFirstChild();
Node name2 = var.getFirstChild();
if (name2.hasChildren()
&& maybeName1.isName()
&& maybeName1.getString().equals(name2.getString())) {
Node thenExpr = thenAssign.getLastChild().detach();
Preconditions.checkState(name2.hasOneChild());
Node elseExpr = name2.removeFirstChild();
placeholder.detach();
Node hookNode = IR.hook(shortCond.getNode(), thenExpr, elseExpr)
.srcref(n);
var.detach();
name2.addChildToBack(hookNode);
parent.replaceChild(n, var);
reportCodeChange();
return var;
}
}
replaceNode(placeholder, unnegatedCond);
return n;
}
/**
* Try to remove duplicate statements from IF blocks. For example:
*
* if (a) {
* x = 1;
* return true;
* } else {
* x = 2;
* return true;
* }
*
* becomes:
*
* if (a) {
* x = 1;
* } else {
* x = 2;
* }
* return true;
*
* @param n The IF node to examine.
*/
private void tryRemoveRepeatedStatements(Node n) {
Preconditions.checkState(n.isIf(), n);
Node parent = n.getParent();
if (!NodeUtil.isStatementBlock(parent)) {
// If the immediate parent is something like a label, we
// can't move the statement, so bail.
return;
}
Node cond = n.getFirstChild();
Node trueBranch = cond.getNext();
Node falseBranch = trueBranch.getNext();
Preconditions.checkNotNull(trueBranch);
Preconditions.checkNotNull(falseBranch);
while (true) {
Node lastTrue = trueBranch.getLastChild();
Node lastFalse = falseBranch.getLastChild();
if (lastTrue == null || lastFalse == null
|| !areNodesEqualForInlining(lastTrue, lastFalse)) {
break;
}
lastTrue.detach();
lastFalse.detach();
parent.addChildAfter(lastTrue, n);
reportCodeChange();
}
}
/**
* @return Whether the node is a block with a single statement that is
* an expression.
*/
private static boolean isFoldableExpressBlock(Node n) {
if (n.isNormalBlock()) {
if (n.hasOneChild()) {
Node maybeExpr = n.getFirstChild();
if (maybeExpr.isExprResult()) {
// IE has a bug where event handlers behave differently when
// their return value is used vs. when their return value is in
// an EXPR_RESULT. It's pretty freaking weird. See:
// http://blickly.github.io/closure-compiler-issues/#291
// We try to detect this case, and not fold EXPR_RESULTs
// into other expressions.
if (maybeExpr.getFirstChild().isCall()) {
Node calledFn = maybeExpr.getFirstFirstChild();
// We only have to worry about methods with an implicit 'this'
// param, or this doesn't happen.
if (calledFn.isGetElem()) {
return false;
} else if (calledFn.isGetProp() &&
calledFn.getLastChild().getString().startsWith("on")) {
return false;
}
}
return true;
}
return false;
}
}
return false;
}
/**
* @return The expression node.
*/
private static Node getBlockExpression(Node n) {
Preconditions.checkState(isFoldableExpressBlock(n));
return n.getFirstChild();
}
/**
* @return Whether the node is a block with a single statement that is
* an return with or without an expression.
*/
private static boolean isReturnBlock(Node n) {
if (n.isNormalBlock()) {
if (n.hasOneChild()) {
Node first = n.getFirstChild();
return first.isReturn();
}
}
return false;
}
/**
* @return Whether the node is a block with a single statement that is
* an return.
*/
private static boolean isReturnExpressBlock(Node n) {
if (n.isNormalBlock()) {
if (n.hasOneChild()) {
Node first = n.getFirstChild();
if (first.isReturn()) {
return first.hasOneChild();
}
}
}
return false;
}
/**
* @return Whether the node is a single return statement.
*/
private static boolean isReturnExpression(Node n) {
if (n.isReturn()) {
return n.hasOneChild();
}
return false;
}
/**
* @return The expression that is part of the return.
*/
private static Node getBlockReturnExpression(Node n) {
Preconditions.checkState(isReturnExpressBlock(n));
return n.getFirstFirstChild();
}
/**
* @return Whether the node is a block with a single statement that is
* a VAR declaration of a single variable.
*/
private static boolean isVarBlock(Node n) {
if (n.isNormalBlock()) {
if (n.hasOneChild()) {
Node first = n.getFirstChild();
if (first.isVar()) {
return first.hasOneChild();
}
}
}
return false;
}
/**
* @return The var node.
*/
private static Node getBlockVar(Node n) {
Preconditions.checkState(isVarBlock(n));
return n.getFirstChild();
}
/**
* Does a statement consume a 'dangling else'? A statement consumes
* a 'dangling else' if an 'else' token following the statement
* would be considered by the parser to be part of the statement.
*/
private static boolean consumesDanglingElse(Node n) {
while (true) {
switch (n.getToken()) {
case IF:
if (n.getChildCount() < 3) {
return true;
}
// This IF node has no else clause.
n = n.getLastChild();
continue;
case BLOCK:
if (n.getChildCount() != 1) {
return false;
}
// This BLOCK has no curly braces.
n = n.getLastChild();
continue;
case WITH:
case WHILE:
case FOR:
case FOR_IN:
n = n.getLastChild();
continue;
default:
return false;
}
}
}
/**
* Whether the node type has lower precedence than "precedence"
*/
static boolean isLowerPrecedence(Node n, final int precedence) {
return NodeUtil.precedence(n.getToken()) < precedence;
}
/**
* Does the expression contain a property assignment?
*/
private static boolean isPropertyAssignmentInExpression(Node n) {
Predicate<Node> isPropertyAssignmentInExpressionPredicate =
new Predicate<Node>() {
@Override
public boolean apply(Node input) {
return (input.isGetProp() &&
input.getParent().isAssign());
}
};
return NodeUtil.has(n, isPropertyAssignmentInExpressionPredicate,
NodeUtil.MATCH_NOT_FUNCTION);
}
/**
* Try to minimize condition expression, as there are additional
* assumptions that can be made when it is known that the final result
* is a boolean.
*
* @return The replacement for n, or the original if no change was made.
*/
private Node tryMinimizeCondition(Node n) {
n = performCoercionSubstitutions(n);
n = performConditionSubstitutions(n);
MinimizedCondition minCond = MinimizedCondition.fromConditionNode(n);
return replaceNode(
minCond.getPlaceholder(),
minCond.getMinimized(MinimizationStyle.PREFER_UNNEGATED));
}
/**
* Replaces 'foo ==/!=/===/!== null' with 'foo' or '!foo'. Should only be used for expressions
* used in conditions where the final result is coerced to a boolean.
*
* @return The replacement for n, or the original if no change was made.
*/
private Node performCoercionSubstitutions(Node n) {
if (!useTypes) {
return n;
}
switch (n.getToken()) {
case OR:
case AND:
performCoercionSubstitutions(n.getFirstChild());
performCoercionSubstitutions(n.getLastChild());
break;
case EQ:
case NE:
case SHEQ:
case SHNE:
return tryReplaceComparisonWithCoercion(n, false /* booleanResult */);
default:
break;
}
return n;
}
/**
* Replaces comparisons (e.g. obj == null, num == 0) with the equivalent type
* coercion (e.g. !obj, !num), if possible.
* @param n a comparison node
* @param booleanResult whether the replacement must evaluate to a boolean
* @return the replacement node or the original node if no replacement was made
*/
private Node tryReplaceComparisonWithCoercion(Node n, boolean booleanResult) {
if (!useTypes) {
return n;
}
Token op = n.getToken();
boolean isShallow = op == Token.SHEQ || op == Token.SHNE;
Preconditions.checkArgument(op == Token.EQ || op == Token.NE || isShallow);
Node left = n.getFirstChild();
Node right = n.getLastChild();
BooleanCoercability booleanCoercability =
canConvertComparisonToBooleanCoercion(left, right, isShallow);
if (booleanCoercability != BooleanCoercability.NONE) {
n.detachChildren();
Node objExpression = booleanCoercability == BooleanCoercability.LEFT ? left : right;
Node replacement;
if (n.getToken() == Token.EQ || n.getToken() == Token.SHEQ) {
replacement = IR.not(objExpression);
} else {
replacement = booleanResult ? IR.not(IR.not(objExpression)) : objExpression;
}
n.replaceWith(replacement);
reportCodeChange();
return replacement;
}
return n;
}
/**
* The ability of a comparison node to be converted to a coercion.
*/
private enum BooleanCoercability {
// Comparison cannot be converted to coercion.
NONE,
// Comparison can be converted to coercion of the left child.
LEFT,
// Comparison can be converted to coercion of the right child.
RIGHT
}
/**
* Determines whether the types on either side of an (in)equality operation
* are amenable to converting to a simple truthiness check. Specifically,
* this is the case when comparing an object type against null or undefined,
* or when comparing a numeric type against zero.
*/
private static BooleanCoercability canConvertComparisonToBooleanCoercion(
Node left, Node right, boolean isShallow) {
// Convert null or undefined check of an object to coercion.
boolean leftIsNull = left.isNull();
boolean rightIsNull = right.isNull();
boolean leftIsUndefined = NodeUtil.isUndefined(left);
boolean rightIsUndefined = NodeUtil.isUndefined(right);
boolean leftIsNullOrUndefined = leftIsNull || leftIsUndefined;
boolean rightIsNullOrUndefined = rightIsNull || rightIsUndefined;
boolean leftIsObjectType = isObjectType(left);
boolean rightIsObjectType = isObjectType(right);
if (isShallow) {
// Shallow compare: must guarantee object cannot be the other type of null/undefined.
if ((leftIsObjectType && !left.getTypeI().isNullable() && rightIsUndefined)
|| (rightIsObjectType && !right.getTypeI().isNullable() && leftIsUndefined)) {
return leftIsNullOrUndefined ? BooleanCoercability.RIGHT : BooleanCoercability.LEFT;
}
} else {
if ((leftIsObjectType && rightIsNullOrUndefined)
|| (rightIsObjectType && leftIsNullOrUndefined)) {
return leftIsNullOrUndefined ? BooleanCoercability.RIGHT : BooleanCoercability.LEFT;
}
}
// Convert comparing a number to zero with coercion.
boolean leftIsZero = (left.isNumber() && left.getDouble() == 0);
boolean rightIsZero = (right.isNumber() && right.getDouble() == 0);
boolean leftIsNumberType = isNumberType(left);
boolean rightIsNumberType = isNumberType(right);
if ((leftIsNumberType && rightIsZero) || (rightIsNumberType && leftIsZero)) {
return leftIsZero ? BooleanCoercability.RIGHT : BooleanCoercability.LEFT;
}
return BooleanCoercability.NONE;
}
/**
* Returns whether the node's type is an object type, which can be
* reduced to a truthiness check when compared against null or undefined.
*/
private static boolean isObjectType(Node n) {
TypeI type = n.getTypeI();
if (type == null) {
return false;
}
type = type.restrictByNotNullOrUndefined();
return !type.isUnknownType()
&& !type.isBottom()
&& !type.isTop()
&& type.isObjectType();
}
/**
* Returns whether the node's type is a numeric type, which can be reduced
* to a truthiness check when compared against zero.
*/
private static boolean isNumberType(Node n) {
TypeI type = n.getTypeI();
if (type == null) {
return false;
}
// Don't restrict by nullable. Nullable numbers are not coercable.
return !type.isUnknownType()
&& !type.isBottom()
&& !type.isTop()
&& type.isNumberValueType();
}
private Node replaceNode(Node lhs, MinimizedCondition.MeasuredNode rhs) {
Node parent = lhs.getParent();
parent.replaceChild(lhs, rhs.getNode());
if (rhs.isChanged()) {
reportCodeChange();
}
return rhs.getNode();
}
/**
* Try to minimize the given condition by applying local substitutions.
*
* The following types of transformations are performed:
* x || true --> true
* x && true --> x
* x ? false : true --> !x
* x ? true : y --> x || y
* x ? x : y --> x || y
*
* Returns the replacement for n, or the original if no change was made
*/
private Node performConditionSubstitutions(Node n) {
Node parent = n.getParent();
switch (n.getToken()) {
case OR:
case AND: {
Node left = n.getFirstChild();
Node right = n.getLastChild();
// Because the expression is in a boolean context minimize
// the children, this can't be done in the general case.
left = performConditionSubstitutions(left);
right = performConditionSubstitutions(right);
// Remove useless conditionals
// Handle the following cases:
// x || false --> x
// x && true --> x
// This works regardless of whether x has side effects.
//
// If x does not have side effects:
// x || true --> true
// x && false --> false
//
// If x may have side effects:
// x || true --> x,true
// x && false --> x,false
//
// In the last two cases, code size may increase slightly (adding
// some parens because the comma operator has a low precedence) but
// the new AST is easier for other passes to handle.
TernaryValue rightVal = NodeUtil.getPureBooleanValue(right);
if (NodeUtil.getPureBooleanValue(right) != TernaryValue.UNKNOWN) {
Token type = n.getToken();
Node replacement = null;
boolean rval = rightVal.toBoolean(true);
// (x || FALSE) => x
// (x && TRUE) => x
if ((type == Token.OR && !rval) || (type == Token.AND && rval)) {
replacement = left;
} else if (!mayHaveSideEffects(left)) {
replacement = right;
} else {
// expr_with_sideeffects || true => expr_with_sideeffects, true
// expr_with_sideeffects && false => expr_with_sideeffects, false
n.detachChildren();
replacement = IR.comma(left, right);
}
if (replacement != null) {
n.detachChildren();
parent.replaceChild(n, replacement);
reportCodeChange();
return replacement;
}
}
return n;
}
case HOOK: {
Node condition = n.getFirstChild();
Node trueNode = n.getSecondChild();
Node falseNode = n.getLastChild();
// Because the expression is in a boolean context minimize
// the result children, this can't be done in the general case.
// The condition is handled in the general case in #optimizeSubtree
trueNode = performConditionSubstitutions(trueNode);
falseNode = performConditionSubstitutions(falseNode);
// Handle five cases:
// x ? true : false --> x
// x ? false : true --> !x
// x ? true : y --> x || y
// x ? y : false --> x && y
// Only when x is NAME, hence x does not have side effects
// x ? x : y --> x || y
Node replacement = null;
TernaryValue trueNodeVal = NodeUtil.getPureBooleanValue(trueNode);
TernaryValue falseNodeVal = NodeUtil.getPureBooleanValue(falseNode);
if (trueNodeVal == TernaryValue.TRUE
&& falseNodeVal == TernaryValue.FALSE) {
// Remove useless conditionals, keep the condition
condition.detach();
replacement = condition;
} else if (trueNodeVal == TernaryValue.FALSE
&& falseNodeVal == TernaryValue.TRUE) {
// Remove useless conditionals, keep the condition
condition.detach();
replacement = IR.not(condition);
} else if (trueNodeVal == TernaryValue.TRUE) {
// Remove useless true case.
n.detachChildren();
replacement = IR.or(condition, falseNode);
} else if (falseNodeVal == TernaryValue.FALSE) {
// Remove useless false case
n.detachChildren();
replacement = IR.and(condition, trueNode);
} else if (!mayHaveSideEffects(condition)
&& !mayHaveSideEffects(trueNode)
&& condition.isEquivalentTo(trueNode)) {
// Remove redundant condition
n.detachChildren();
replacement = IR.or(trueNode, falseNode);
}
if (replacement != null) {
parent.replaceChild(n, replacement);
n = replacement;
reportCodeChange();
}
return n;
}
default:
// while(true) --> while(1)
TernaryValue nVal = NodeUtil.getPureBooleanValue(n);
if (nVal != TernaryValue.UNKNOWN) {
boolean result = nVal.toBoolean(true);
int equivalentResult = result ? 1 : 0;
return maybeReplaceChildWithNumber(n, parent, equivalentResult);
}
// We can't do anything else currently.
return n;
}
}
/**
* Replaces a node with a number node if the new number node is not equivalent
* to the current node.
*
* Returns the replacement for n if it was replaced, otherwise returns n.
*/
private Node maybeReplaceChildWithNumber(Node n, Node parent, int num) {
Node newNode = IR.number(num);
if (!newNode.isEquivalentTo(n)) {
parent.replaceChild(n, newNode);
reportCodeChange();
return newNode;
}
return n;
}
}