/*
* Copyright 2008 Google Inc.
*
* 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.gwt.dev.js;
import com.google.gwt.dev.jjs.HasSourceInfo;
import com.google.gwt.dev.jjs.SourceInfo;
import com.google.gwt.dev.js.ast.CanBooleanEval;
import com.google.gwt.dev.js.ast.JsBinaryOperation;
import com.google.gwt.dev.js.ast.JsBinaryOperator;
import com.google.gwt.dev.js.ast.JsBlock;
import com.google.gwt.dev.js.ast.JsBooleanLiteral;
import com.google.gwt.dev.js.ast.JsBreak;
import com.google.gwt.dev.js.ast.JsConditional;
import com.google.gwt.dev.js.ast.JsContext;
import com.google.gwt.dev.js.ast.JsContinue;
import com.google.gwt.dev.js.ast.JsDoWhile;
import com.google.gwt.dev.js.ast.JsExprStmt;
import com.google.gwt.dev.js.ast.JsExpression;
import com.google.gwt.dev.js.ast.JsFor;
import com.google.gwt.dev.js.ast.JsFunction;
import com.google.gwt.dev.js.ast.JsIf;
import com.google.gwt.dev.js.ast.JsModVisitor;
import com.google.gwt.dev.js.ast.JsNullLiteral;
import com.google.gwt.dev.js.ast.JsNumberLiteral;
import com.google.gwt.dev.js.ast.JsPrefixOperation;
import com.google.gwt.dev.js.ast.JsProgram;
import com.google.gwt.dev.js.ast.JsStatement;
import com.google.gwt.dev.js.ast.JsStringLiteral;
import com.google.gwt.dev.js.ast.JsUnaryOperation;
import com.google.gwt.dev.js.ast.JsUnaryOperator;
import com.google.gwt.dev.js.ast.JsValueLiteral;
import com.google.gwt.dev.js.ast.JsVars;
import com.google.gwt.dev.js.ast.JsVisitable;
import com.google.gwt.dev.js.ast.JsVisitor;
import com.google.gwt.dev.js.ast.JsWhile;
import com.google.gwt.dev.js.ast.JsVars.JsVar;
import java.util.ArrayList;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Removes JsFunctions that are never referenced in the program.
*/
public class JsStaticEval {
/**
* Examines code to find out whether it contains any break or continue
* statements.
*
* TODO: We could be more sophisticated with this. A nested while loop with an
* unlabeled break should not cause this visitor to return false. Nor should a
* labeled break break to another context.
*/
public static class FindBreakContinueStatementsVisitor extends JsVisitor {
private boolean hasBreakContinueStatements = false;
@Override
public void endVisit(JsBreak x, JsContext<JsStatement> ctx) {
hasBreakContinueStatements = true;
}
@Override
public void endVisit(JsContinue x, JsContext<JsStatement> ctx) {
hasBreakContinueStatements = true;
}
protected boolean hasBreakContinueStatements() {
return hasBreakContinueStatements;
}
}
/**
* Creates a minimalist list of statements that must be run in order to
* achieve the same declaration effect as the visited statements.
*
* For example, a JsFunction declaration should be run as a JsExprStmt. JsVars
* should be run without any initializers.
*
* This visitor is called from
* {@link StaticEvalVisitor#ensureDeclarations(JsStatement)} on any statements
* that are removed from a function.
*/
private static class MustExecVisitor extends JsVisitor {
private final List<JsStatement> mustExec = new ArrayList<JsStatement>();
public MustExecVisitor() {
}
@Override
public void endVisit(JsExprStmt x, JsContext<JsStatement> ctx) {
JsFunction func = isFunctionDecl(x);
if (func != null) {
mustExec.add(x);
}
}
@Override
public void endVisit(JsVars x, JsContext<JsStatement> ctx) {
JsVars strippedVars = new JsVars(x.getSourceInfo().makeChild(
MustExecVisitor.class, "Simplified execution"));
boolean mustReplace = false;
for (JsVar var : x) {
JsVar strippedVar = new JsVar(var.getSourceInfo().makeChild(
MustExecVisitor.class, "Simplified execution"), var.getName());
strippedVars.add(strippedVar);
if (var.getInitExpr() != null) {
mustReplace = true;
}
}
if (mustReplace) {
mustExec.add(strippedVars);
} else {
mustExec.add(x);
}
}
public List<JsStatement> getStatements() {
return mustExec;
}
@Override
public boolean visit(JsFunction x, JsContext<JsExpression> ctx) {
// Don't dive into nested functions.
return false;
}
}
/**
* Does static evals.
*
* TODO: borrow more concepts from
* {@link com.google.gwt.dev.jjs.impl.DeadCodeElimination}, such as ignored
* expression results.
*/
private class StaticEvalVisitor extends JsModVisitor {
private Set<JsExpression> evalBooleanContext = new HashSet<JsExpression>();
/**
* This is used by {@link #additionCoercesToString}.
*/
private Map<JsExpression, Boolean> coercesToStringMap = new IdentityHashMap<JsExpression, Boolean>();
@Override
public void endVisit(JsBinaryOperation x, JsContext<JsExpression> ctx) {
JsBinaryOperator op = x.getOperator();
JsExpression arg1 = x.getArg1();
JsExpression arg2 = x.getArg2();
if (MATH_ASSOCIATIVE.contains(op)
&& trySimplifyAssociativeExpression(x, ctx)) {
// Nothing else to do
} else if (op == JsBinaryOperator.AND) {
shortCircuitAnd(arg1, arg2, ctx);
} else if (op == JsBinaryOperator.OR) {
shortCircuitOr(arg1, arg2, ctx);
} else if (op == JsBinaryOperator.COMMA) {
trySimplifyComma(arg1, arg2, ctx);
} else if (op == JsBinaryOperator.EQ) {
trySimplifyEq(x, arg1, arg2, ctx);
} else if (op == JsBinaryOperator.NEQ) {
trySimplifyNe(x, arg1, arg2, ctx);
} else if (op == JsBinaryOperator.ADD) {
trySimplifyAdd(x, arg1, arg2, ctx);
}
}
/**
* Prune dead statements and empty blocks.
*/
@Override
public void endVisit(JsBlock x, JsContext<JsStatement> ctx) {
/*
* Remove any dead statements after an abrupt change in code flow and
* promote safe statements within nested blocks to this block.
*/
List<JsStatement> stmts = x.getStatements();
for (int i = 0; i < stmts.size(); i++) {
JsStatement stmt = stmts.get(i);
if (stmt instanceof JsBlock) {
// Promote a sub-block's children to the current block.
JsBlock block = (JsBlock) stmt;
stmts.remove(i);
stmts.addAll(i, block.getStatements());
i--;
didChange = true;
continue;
}
if (stmt.unconditionalControlBreak()) {
// Abrupt change in flow, chop the remaining items from this block
for (int j = i + 1; j < stmts.size();) {
JsStatement toRemove = stmts.get(j);
JsStatement toReplace = ensureDeclarations(toRemove);
if (toReplace == null) {
stmts.remove(j);
didChange = true;
} else if (toReplace == toRemove) {
++j;
} else {
stmts.set(j, toReplace);
didChange = true;
}
}
}
}
if (ctx.canRemove() && stmts.size() == 0) {
// Remove blocks with no effect
ctx.removeMe();
}
}
@Override
public void endVisit(JsConditional x, JsContext<JsExpression> ctx) {
evalBooleanContext.remove(x.getTestExpression());
JsExpression condExpr = x.getTestExpression();
JsExpression thenExpr = x.getThenExpression();
JsExpression elseExpr = x.getElseExpression();
if (condExpr instanceof CanBooleanEval) {
CanBooleanEval condEval = (CanBooleanEval) condExpr;
if (condEval.isBooleanTrue()) {
JsBinaryOperation binOp = new JsBinaryOperation(makeSourceInfo(x,
"Simplified always-true condition"), JsBinaryOperator.AND,
condExpr, thenExpr);
ctx.replaceMe(accept(binOp));
} else if (condEval.isBooleanFalse()) {
// e.g. (false() ? then : else) -> false() || else
JsBinaryOperation binOp = new JsBinaryOperation(makeSourceInfo(x,
"Simplified always-false condition"), JsBinaryOperator.OR,
condExpr, elseExpr);
ctx.replaceMe(accept(binOp));
}
}
}
/**
* Convert do { } while (false); into a block.
*/
@Override
public void endVisit(JsDoWhile x, JsContext<JsStatement> ctx) {
evalBooleanContext.remove(x.getCondition());
JsExpression expr = x.getCondition();
if (expr instanceof CanBooleanEval) {
CanBooleanEval cond = (CanBooleanEval) expr;
// If false, replace do with do's body
if (cond.isBooleanFalse()) {
// Unless it contains break/continue statements
FindBreakContinueStatementsVisitor visitor = new FindBreakContinueStatementsVisitor();
visitor.accept(x.getBody());
if (!visitor.hasBreakContinueStatements()) {
JsBlock block = new JsBlock(makeSourceInfo(x,
"Simplified always-false condition"));
block.getStatements().add(x.getBody());
block.getStatements().add(expr.makeStmt());
ctx.replaceMe(accept(block));
}
}
}
}
@Override
public void endVisit(JsExprStmt x, JsContext<JsStatement> ctx) {
if (!x.getExpression().hasSideEffects()) {
if (ctx.canRemove()) {
ctx.removeMe();
} else {
ctx.replaceMe(program.getEmptyStmt());
}
}
}
/**
* Prune for (X; false(); Y) statements, make sure X and false() are run.
*/
@Override
public void endVisit(JsFor x, JsContext<JsStatement> ctx) {
evalBooleanContext.remove(x.getCondition());
JsExpression expr = x.getCondition();
if (expr instanceof CanBooleanEval) {
CanBooleanEval cond = (CanBooleanEval) expr;
// If false, replace with initializers and condition.
if (cond.isBooleanFalse()) {
JsBlock block = new JsBlock(makeSourceInfo(x,
"Simplified always-false condition"));
if (x.getInitExpr() != null) {
block.getStatements().add(x.getInitExpr().makeStmt());
}
if (x.getInitVars() != null) {
block.getStatements().add(x.getInitVars());
}
block.getStatements().add(expr.makeStmt());
JsStatement decls = ensureDeclarations(x.getBody());
if (decls != null) {
block.getStatements().add(decls);
}
ctx.replaceMe(accept(block));
}
}
}
/**
* Simplify if statements.
*/
@Override
public void endVisit(JsIf x, JsContext<JsStatement> ctx) {
evalBooleanContext.remove(x.getIfExpr());
JsExpression condExpr = x.getIfExpr();
if (condExpr instanceof CanBooleanEval) {
if (tryStaticEvalIf(x, (CanBooleanEval) condExpr, ctx)) {
return;
}
}
JsStatement thenStmt = x.getThenStmt();
JsStatement elseStmt = x.getElseStmt();
boolean thenIsEmpty = isEmpty(thenStmt);
boolean elseIsEmpty = isEmpty(elseStmt);
JsExpression thenExpr = extractExpression(thenStmt);
JsExpression elseExpr = extractExpression(elseStmt);
if (thenIsEmpty && elseIsEmpty) {
// Convert "if (a()) {}" => "a()".
ctx.replaceMe(condExpr.makeStmt());
} else if (thenExpr != null && elseExpr != null) {
// Convert "if (a()) {b()} else {c()}" => "a()?b():c()".
JsConditional cond = new JsConditional(makeSourceInfo(x,
"Replaced if statement with conditional"), x.getIfExpr(), thenExpr,
elseExpr);
ctx.replaceMe(accept(cond.makeStmt()));
} else if (thenIsEmpty && elseExpr != null) {
// Convert "if (a()) {} else {b()}" => a()||b().
JsBinaryOperation op = new JsBinaryOperation(makeSourceInfo(x,
"Replaced if statement with ||"), JsBinaryOperator.OR,
x.getIfExpr(), elseExpr);
ctx.replaceMe(accept(op.makeStmt()));
} else if (thenIsEmpty && !elseIsEmpty) {
// Convert "if (a()) {} else {stuff}" => "if (!a()) {stuff}".
JsUnaryOperation negatedOperation = new JsPrefixOperation(
makeSourceInfo(x, "Simplified if with empty then statement"),
JsUnaryOperator.NOT, x.getIfExpr());
JsIf newIf = new JsIf(makeSourceInfo(x,
"Simplified if with empty then statement"), negatedOperation,
elseStmt, null);
ctx.replaceMe(accept(newIf));
} else if (elseIsEmpty && thenExpr != null) {
// Convert "if (a()) {b()}" => "a()&&b()".
JsBinaryOperation op = new JsBinaryOperation(makeSourceInfo(x,
"Replaced if statement with &&"), JsBinaryOperator.AND,
x.getIfExpr(), thenExpr);
ctx.replaceMe(accept(op.makeStmt()));
} else if (elseIsEmpty && elseStmt != null) {
// Convert "if (a()) {b()} else {}" => "if (a()) {b()}".
JsIf newIf = new JsIf(makeSourceInfo(x, "Pruned empty else statement"),
x.getIfExpr(), thenStmt, null);
ctx.replaceMe(accept(newIf));
}
}
/**
* Change !!x to x in a boolean context.
*/
@Override
public void endVisit(JsPrefixOperation x, JsContext<JsExpression> ctx) {
if (x.getOperator() == JsUnaryOperator.NOT) {
evalBooleanContext.remove(x.getArg());
}
if (evalBooleanContext.contains(x)) {
if ((x.getOperator() == JsUnaryOperator.NOT)
&& (x.getArg() instanceof JsPrefixOperation)) {
JsPrefixOperation arg = (JsPrefixOperation) x.getArg();
if (arg.getOperator() == JsUnaryOperator.NOT) {
ctx.replaceMe(arg.getArg());
return;
}
}
}
}
/**
* Prune while (false) statements.
*/
@Override
public void endVisit(JsWhile x, JsContext<JsStatement> ctx) {
evalBooleanContext.remove(x.getCondition());
JsExpression expr = x.getCondition();
if (expr instanceof CanBooleanEval) {
CanBooleanEval cond = (CanBooleanEval) expr;
// If false, replace with condition.
if (cond.isBooleanFalse()) {
JsBlock block = new JsBlock(makeSourceInfo(x,
"Simplified always-false condition"));
block.getStatements().add(expr.makeStmt());
JsStatement decls = ensureDeclarations(x.getBody());
if (decls != null) {
block.getStatements().add(decls);
}
ctx.replaceMe(accept(block));
}
}
}
@Override
public boolean visit(JsConditional x, JsContext<JsExpression> ctx) {
evalBooleanContext.add(x.getTestExpression());
return true;
}
@Override
public boolean visit(JsDoWhile x, JsContext<JsStatement> ctx) {
evalBooleanContext.add(x.getCondition());
return true;
}
@Override
public boolean visit(JsFor x, JsContext<JsStatement> ctx) {
evalBooleanContext.add(x.getCondition());
return true;
}
@Override
public boolean visit(JsIf x, JsContext<JsStatement> ctx) {
evalBooleanContext.add(x.getIfExpr());
return true;
}
@Override
public boolean visit(JsPrefixOperation x, JsContext<JsExpression> ctx) {
if (x.getOperator() == JsUnaryOperator.NOT) {
evalBooleanContext.add(x.getArg());
}
return true;
}
@Override
public boolean visit(JsWhile x, JsContext<JsStatement> ctx) {
evalBooleanContext.add(x.getCondition());
return true;
}
/**
* Given an expression, determine if the addition operator would cause a
* string coercion to happen.
*/
private boolean additionCoercesToString(JsExpression expr) {
if (expr instanceof JsStringLiteral) {
return true;
}
/*
* Because the nodes passed into this method are visited on exit, it is
* worthwile to memoize the result for this function.
*/
Boolean toReturn = coercesToStringMap.get(expr);
if (toReturn != null) {
return toReturn;
}
toReturn = false;
if (expr instanceof JsBinaryOperation) {
JsBinaryOperation op = (JsBinaryOperation) expr;
switch (op.getOperator()) {
case ADD:
toReturn = additionCoercesToString(op.getArg1())
|| additionCoercesToString(op.getArg2());
break;
case COMMA:
toReturn = additionCoercesToString(op.getArg2());
break;
}
if (op.getOperator().isAssignment()) {
toReturn = additionCoercesToString(op.getArg2());
}
}
/*
* TODO: Consider adding heuristics to detect String(foo), typeof(foo),
* and foo.toString(). The latter is debatable, since an implementation
* might not actually return a string.
*/
coercesToStringMap.put(expr, toReturn);
return toReturn;
}
private boolean appendLiteral(StringBuilder result, JsValueLiteral val) {
if (val instanceof JsNumberLiteral) {
double number = ((JsNumberLiteral) val).getValue();
result.append(fixTrailingZeroes(String.valueOf(number)));
} else if (val instanceof JsStringLiteral) {
result.append(((JsStringLiteral) val).getValue());
} else if (val instanceof JsBooleanLiteral) {
result.append(((JsBooleanLiteral) val).getValue());
} else if (val instanceof JsNullLiteral) {
result.append("null");
} else {
return false;
}
return true;
}
/**
* This method MUST be called whenever any statements are removed from a
* function. This is because some statements, such as JsVars or JsFunction
* have the effect of defining local variables, no matter WHERE they are in
* the function. The returned statement (if any), must be executed. It is
* also possible for stmt to be directly returned, in which case the caller
* should not perform AST changes that would cause an infinite optimization
* loop.
*
* Note: EvalFunctionsAtTopScope will have changed any JsFunction
* declarations into statements before this visitor runs.
*/
private JsStatement ensureDeclarations(JsStatement stmt) {
if (stmt == null) {
return null;
}
MustExecVisitor mev = new MustExecVisitor();
mev.accept(stmt);
List<JsStatement> stmts = mev.getStatements();
if (stmts.isEmpty()) {
return null;
} else if (stmts.size() == 1) {
return stmts.get(0);
} else {
JsBlock jsBlock = new JsBlock(makeSourceInfo(stmt,
"Ensuring declarations"));
jsBlock.getStatements().addAll(stmts);
return jsBlock;
}
}
/*
* String.valueOf(Double) produces trailing .0 on integers which is
* incorrect for Javascript which produces conversions to string without
* trailing zeroes. Without this, int + String will turn out wrong.
*/
private String fixTrailingZeroes(String num) {
if (num.endsWith(".0")) {
String fixNum = num.substring(0, num.length() - 2);
assert Double.parseDouble(fixNum) == Double.parseDouble(num);
num = fixNum;
}
return num;
}
private SourceInfo makeSourceInfo(HasSourceInfo x, String m) {
return x.getSourceInfo().makeChild(StaticEvalVisitor.class, m);
}
private JsExpression simplifyEq(JsExpression original, JsExpression arg1,
JsExpression arg2) {
assert (original != null);
if (arg1 instanceof JsNullLiteral) {
return simplifyNullEq(original, arg2);
}
if (arg2 instanceof JsNullLiteral) {
return simplifyNullEq(original, arg1);
}
// no simplification made
return original;
}
private JsExpression simplifyNe(JsExpression original, JsExpression arg1,
JsExpression arg2) {
assert (original != null);
if (arg1 instanceof JsNullLiteral) {
return simplifyNullNe(original, arg2);
}
if (arg2 instanceof JsNullLiteral) {
return simplifyNullNe(original, arg1);
}
// no simplification made
return original;
}
/**
* Simplify exp == null.
*/
private JsExpression simplifyNullEq(JsExpression original, JsExpression exp) {
assert (original != null);
if (exp instanceof JsValueLiteral) {
// "undefined" is not a JsValueLiteral, so the only way
// the result can be true is if exp is itself a JsNullLiteral
boolean result = exp instanceof JsNullLiteral;
return program.getBooleanLiteral(result);
}
// no simplification made
return original;
}
/**
* Simplify exp != null.
*/
private JsExpression simplifyNullNe(JsExpression original, JsExpression exp) {
assert (original != null);
if (exp instanceof JsValueLiteral) {
// "undefined" is not a JsValueLiteral, so the only way
// the result can be false is if exp is itself a JsNullLiteral
boolean result = !(exp instanceof JsNullLiteral);
return program.getBooleanLiteral(result);
}
// no simplification made
return original;
}
/**
* Simplify a + b.
*/
private void trySimplifyAdd(JsExpression original, JsExpression arg1,
JsExpression arg2, JsContext<JsExpression> ctx) {
if (arg1 instanceof JsValueLiteral && arg2 instanceof JsValueLiteral) {
// case: number + number
if (arg1 instanceof JsNumberLiteral && arg2 instanceof JsNumberLiteral) {
double value = ((JsNumberLiteral) arg1).getValue()
+ ((JsNumberLiteral) arg2).getValue();
ctx.replaceMe(program.getNumberLiteral(value));
} else {
// cases: number + string or string + number
StringBuilder result = new StringBuilder();
if (appendLiteral(result, (JsValueLiteral) arg1)
&& appendLiteral(result, (JsValueLiteral) arg2)) {
ctx.replaceMe(program.getStringLiteral(original.getSourceInfo(),
result.toString()));
}
}
}
}
/**
* Attempts to simplify adjoining binary expressions with mathematically
* associative operators. This pass also tries to make these binary
* expressions as left-normal as possible.
*/
private boolean trySimplifyAssociativeExpression(JsBinaryOperation x,
JsContext<JsExpression> ctx) {
boolean toReturn = false;
JsBinaryOperator op = x.getOperator();
JsExpression arg1 = x.getArg1();
JsExpression arg2 = x.getArg2();
/*
* First, we'll try to normalize the nesting of any binary expressions
* that we encounter. If we do this correctly,it will help to cut down on
* the number of unnecessary parens in the emitted JS.
*/
// (X) O (c O d) ==> ((X) O c) O d
{
JsBinaryOperation rightOp = null;
if (arg2 instanceof JsBinaryOperation) {
rightOp = (JsBinaryOperation) arg2;
}
if (rightOp != null && !rightOp.getOperator().isAssignment()
&& op == rightOp.getOperator()) {
if (op == JsBinaryOperator.ADD) {
/*
* JS type coercion is a problem if we don't know for certain that
* the right-hand expression will definitely be evaluated in a
* string context.
*/
boolean mustBeString = additionCoercesToString(rightOp.getArg1())
|| (additionCoercesToString(arg1) && additionCoercesToString(rightOp.getArg2()));
if (!mustBeString) {
return toReturn;
}
}
// (X) O c --> Try to reduce this
JsExpression newLeft = new JsBinaryOperation(x.getSourceInfo(), op,
arg1, rightOp.getArg1());
// Reset local vars with new state
op = rightOp.getOperator();
arg1 = accept(newLeft);
arg2 = rightOp.getArg2();
x = new JsBinaryOperation(x.getSourceInfo(), op, arg1, arg2);
ctx.replaceMe(x);
toReturn = didChange = true;
}
}
/*
* Now that we know that our AST is as left-normal as we can make it
* (because this method is called from endVisit), we now try to simplify
* the left-right node and the right node.
*/
// (a O b) O c ==> a O s
{
JsBinaryOperation leftOp = null;
JsExpression leftLeft = null;
JsExpression leftRight = null;
if (arg1 instanceof JsBinaryOperation) {
leftOp = (JsBinaryOperation) arg1;
if (op.getPrecedence() == leftOp.getOperator().getPrecedence()) {
leftLeft = leftOp.getArg1();
leftRight = leftOp.getArg2();
}
}
if (leftRight != null) {
if (op == JsBinaryOperator.ADD) {
// Behavior as described above
boolean mustBeString = additionCoercesToString(leftRight)
|| (additionCoercesToString(leftLeft) && additionCoercesToString(arg2));
if (!mustBeString) {
return toReturn;
}
}
// (b O c)
JsBinaryOperation middle = new JsBinaryOperation(x.getSourceInfo(),
op, leftRight, arg2);
StaticEvalVisitor v = new StaticEvalVisitor();
JsExpression maybeSimplified = v.accept(middle);
if (v.didChange()) {
x.setArg1(leftLeft);
x.setArg2(maybeSimplified);
toReturn = didChange = true;
}
}
}
return toReturn;
}
private void trySimplifyEq(JsExpression original, JsExpression arg1,
JsExpression arg2, JsContext<JsExpression> ctx) {
JsExpression updated = simplifyEq(original, arg1, arg2);
if (updated != original) {
ctx.replaceMe(updated);
}
}
private void trySimplifyNe(JsExpression original, JsExpression arg1,
JsExpression arg2, JsContext<JsExpression> ctx) {
JsExpression updated = simplifyNe(original, arg1, arg2);
if (updated != original) {
ctx.replaceMe(updated);
}
}
private boolean tryStaticEvalIf(JsIf x, CanBooleanEval cond,
JsContext<JsStatement> ctx) {
JsStatement thenStmt = x.getThenStmt();
JsStatement elseStmt = x.getElseStmt();
if (cond.isBooleanTrue()) {
JsBlock block = new JsBlock(makeSourceInfo(x,
"Simplified always-true condition"));
block.getStatements().add(x.getIfExpr().makeStmt());
if (thenStmt != null) {
block.getStatements().add(thenStmt);
}
JsStatement decls = ensureDeclarations(elseStmt);
if (decls != null) {
block.getStatements().add(decls);
}
ctx.replaceMe(accept(block));
return true;
} else if (cond.isBooleanFalse()) {
JsBlock block = new JsBlock(makeSourceInfo(x,
"Simplified always-false condition"));
block.getStatements().add(x.getIfExpr().makeStmt());
if (elseStmt != null) {
block.getStatements().add(elseStmt);
}
JsStatement decls = ensureDeclarations(thenStmt);
if (decls != null) {
block.getStatements().add(decls);
}
ctx.replaceMe(accept(block));
return true;
} else {
return false;
}
}
}
/**
* A set of the JS operators that are mathematically associative in nature.
*/
private static final Set<JsBinaryOperator> MATH_ASSOCIATIVE = EnumSet.of(
JsBinaryOperator.ADD, JsBinaryOperator.AND, JsBinaryOperator.BIT_AND,
JsBinaryOperator.BIT_OR, JsBinaryOperator.BIT_XOR,
JsBinaryOperator.COMMA, JsBinaryOperator.MUL, JsBinaryOperator.OR);
public static boolean exec(JsProgram program) {
return (new JsStaticEval(program)).execImpl();
}
public static <T extends JsVisitable> T exec(JsProgram program, T node) {
return (new JsStaticEval(program)).execImpl(node);
}
/**
* Attempts to extract a single expression from a given statement and returns
* it. If no such expression exists, returns <code>null</code>.
*/
protected static JsExpression extractExpression(JsStatement stmt) {
if (stmt == null) {
return null;
}
if (stmt instanceof JsExprStmt) {
return ((JsExprStmt) stmt).getExpression();
}
if (stmt instanceof JsBlock && ((JsBlock) stmt).getStatements().size() == 1) {
return extractExpression(((JsBlock) stmt).getStatements().get(0));
}
return null;
}
protected static boolean isEmpty(JsStatement stmt) {
if (stmt == null) {
return true;
}
return (stmt instanceof JsBlock && ((JsBlock) stmt).getStatements().isEmpty());
}
/**
* If the statement is a JsExprStmt that declares a function with no other
* side effects, returns that function; otherwise <code>null</code>.
*/
protected static JsFunction isFunctionDecl(JsStatement stmt) {
if (stmt instanceof JsExprStmt) {
JsExprStmt exprStmt = (JsExprStmt) stmt;
JsExpression expr = exprStmt.getExpression();
if (expr instanceof JsFunction) {
JsFunction func = (JsFunction) expr;
if (func.getName() != null) {
return func;
}
}
}
return null;
}
/**
* Simplify short circuit AND expressions.
*
* <pre>
* if (true && isWhatever()) -> if (isWhatever()), unless side effects
* if (false() && isWhatever()) -> if (false())
* </pre>
*/
protected static void shortCircuitAnd(JsExpression arg1, JsExpression arg2,
JsContext<JsExpression> ctx) {
if (arg1 instanceof CanBooleanEval) {
CanBooleanEval eval1 = (CanBooleanEval) arg1;
if (eval1.isBooleanTrue() && !arg1.hasSideEffects()) {
ctx.replaceMe(arg2);
} else if (eval1.isBooleanFalse()) {
ctx.replaceMe(arg1);
}
}
}
/**
* Simplify short circuit OR expressions.
*
* <pre>
* if (true() || isWhatever()) -> if (true())
* if (false || isWhatever()) -> if (isWhatever()), unless side effects
* </pre>
*/
protected static void shortCircuitOr(JsExpression arg1, JsExpression arg2,
JsContext<JsExpression> ctx) {
if (arg1 instanceof CanBooleanEval) {
CanBooleanEval eval1 = (CanBooleanEval) arg1;
if (eval1.isBooleanTrue()) {
ctx.replaceMe(arg1);
} else if (eval1.isBooleanFalse() && !arg1.hasSideEffects()) {
ctx.replaceMe(arg2);
}
}
}
protected static void trySimplifyComma(JsExpression arg1, JsExpression arg2,
JsContext<JsExpression> ctx) {
if (!arg1.hasSideEffects()) {
ctx.replaceMe(arg2);
}
}
private final JsProgram program;
public JsStaticEval(JsProgram program) {
this.program = program;
}
public boolean execImpl() {
StaticEvalVisitor sev = new StaticEvalVisitor();
sev.accept(program);
return sev.didChange();
}
public <T extends JsVisitable> T execImpl(T node) {
return new StaticEvalVisitor().accept(node);
}
}