com.google.gwt.dev.jjs.impl

Class Simplifier

java.lang.Object

com.google.gwt.dev.jjs.impl.Simplifier

public class Simplifier
extends Object

Methods that both construct and try to simplify AST nodes. If simplification fails, then the methods will return an original, unmodified version of the node if one is supplied. The routines do not recurse into their arguments; the arguments are assumed to already be simplified as much as possible.

Method Summary

Modifier and Type	Method and Description
static JExpression	and(JBinaryOperation exp) Simplify short circuit AND expressions.
static JExpression	cast(JCastOperation exp) Simplify cast operations.
static JExpression	cast(JType type, JExpression exp) Simplify cast operations.
static JExpression	conditional(JConditional exp) Simplify conditional expressions.
static JStatement	ifStatement(JIfStatement stmt, JMethod currentMethod) Simplifies an ifthenelse statement.
static boolean	isEmpty(JStatement stmt) TODO: if the AST were normalized, we wouldn't need this.
static JExpression	not(JPrefixOperation expr) Simplifies an negation expression.
static JExpression	or(JBinaryOperation exp) Simplify short circuit OR expressions.

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, toString

Method Detail

isEmpty

public static boolean isEmpty(JStatement stmt)

TODO: if the AST were normalized, we wouldn't need this.

cast

public static JExpression cast(JType type,
                               JExpression exp)

Simplify cast operations. Used when creating a cast in DeadCodeElimination. For simplifying casts that are actually in the AST, cast(JCastOperation) is used instead.

 (int) 1 -> 1
 (A) (a,b) -> (a, (A) b)
 

Parameters:

type - the Type to cast the expression exp to.

exp - the current JExpression under the cast as it is being simplified.

Returns:

the simplified expression.

cast

public static JExpression cast(JCastOperation exp)

Simplify cast operations.

 (int) 1 -> 1
 (A) (a,b) -> (a, (A) b)
 

Parameters:

exp - a JCastOperation to be simplified.

Returns:

the simplified expression if a simplification was possible; exp otherwise.

conditional

public static JExpression conditional(JConditional exp)

Simplify conditional expressions.

 (a,b,c)?d:e -> a,b,(c?d:e)
 true ? then : else -> then
 false ? then : else -> else
 cond ? true : else) -> cond || else
 cond ? false : else -> !cond && else
 cond ? then : true -> !cond || then
 cond ? then : false -> cond && then
 !cond ? then : else -> cond ? else : then
 

Parameters:

exp - a JCondintional to be simplified.

Returns:

the simplified expression if a simplification was possible; exp otherwise.

ifStatement

public static JStatement ifStatement(JIfStatement stmt,
                                     JMethod currentMethod)

Simplifies an ifthenelse statement.

 if(a,b,c) d [else e] -> {a; b; if(c) d [else e]; }
 if(true) a [else b] -> a
 if(false) a else b -> b
 if(notImpl(c)) a else b -> if(c) b else a
 if(true) ; else b -> true
 if(false) a [else ;] -> false
 if(c) ; [else ;] -> c

Parameters:

stmt - the statement to simplify.

currentMethod - the method where the statement resides

Returns:

the simplified statement if a simplification could be done and stmt otherwise.

not

public static JExpression not(JPrefixOperation expr)

Simplifies an negation expression. if(a,b,c) d else e -> {a; b; if(c) d else e; }

Parameters:

expr - the expression to simplify.

Returns:

the simplified expression if a simplification could be done and expr otherwise.

and

public static JExpression and(JBinaryOperation exp)

Simplify short circuit AND expressions.

 true && isWhatever() -> isWhatever()
 false && isWhatever() -> false

 isWhatever() && true -> isWhatever()
 isWhatever() && false -> false, unless side effects

 (a, b) && c -> (a, b && c)
 

Parameters:

exp - an AND JBinaryExpression to be simplified.

Returns:

the simplified expression if a simplification was possible; exp otherwise.

or

public static JExpression or(JBinaryOperation exp)

Simplify short circuit OR expressions.

 true || isWhatever() -> true
 false || isWhatever() -> isWhatever()

 isWhatever() || false isWhatever()
 isWhatever() || true -> true, unless side effects

 (a, b) || c -> (a, b || c)
 

Parameters:

exp - an OR JBinaryExpression to be simplified.

Returns:

the simplified expression if a simplification was possible; exp otherwise.