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improve compression of undefined, NaN & Infinitiy (#1748)

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- migrate transformation logic from `OutputStream` to `Compressor`
- always turn `undefined` into `void 0` (unless `unsafe`)
- always keep `NaN` except when avoiding local variable redefinition
- introduce `keep_infinity` to suppress `1/0` transform, except when avoiding local variable redefinition

supersedes #1723
fixes #1730
This commit is contained in:
Alex Lam S.L
2017-04-01 03:02:14 +08:00
committed by GitHub
parent 1ddc05725d
commit 257ddc3bdb
9 changed files with 170 additions and 56 deletions
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75
lib/compress.js
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@@ -66,6 +66,7 @@ function Compressor(options, false_by_default) {
join_vars : !false_by_default,
keep_fargs : true,
keep_fnames : false,
keep_infinity : false,
loops : !false_by_default,
negate_iife : !false_by_default,
passes : 1,
@@ -215,7 +216,12 @@ merge(Compressor.prototype, {
}) : make_node(AST_EmptyStatement, node);
}
return make_node(AST_SimpleStatement, node, {
body: node.value || make_node(AST_Undefined, node)
body: node.value || make_node(AST_UnaryPrefix, node, {
operator: "void",
expression: make_node(AST_Number, node, {
value: 0
})
})
});
}
if (node instanceof AST_Lambda && node !== self) {
@@ -1123,8 +1129,12 @@ merge(Compressor.prototype, {
}));
};
function is_undefined(node) {
return node instanceof AST_Undefined || node.is_undefined;
function is_undefined(node, compressor) {
return node.is_undefined
|| node instanceof AST_Undefined
|| node instanceof AST_UnaryPrefix
&& node.operator == "void"
&& !node.expression.has_side_effects(compressor);
}
/* -----[ boolean/negation helpers ]----- */
@@ -1313,7 +1323,7 @@ merge(Compressor.prototype, {
return this;
}
});
var unaryPrefix = makePredicate("! ~ - +");
var unaryPrefix = makePredicate("! ~ - + void");
AST_Node.DEFMETHOD("is_constant", function(){
// Accomodate when compress option evaluate=false
// as well as the common constant expressions !0 and -1
@@ -2971,7 +2981,7 @@ merge(Compressor.prototype, {
}
}
}
if (is_undefined(self.cdr)) {
if (is_undefined(self.cdr, compressor)) {
return make_node(AST_UnaryPrefix, self, {
operator : "void",
expression : self.car
@@ -3010,7 +3020,7 @@ merge(Compressor.prototype, {
self.expression = e;
return self;
} else {
return make_node(AST_Undefined, self).transform(compressor);
return make_node(AST_Undefined, self).optimize(compressor);
}
}
if (compressor.option("booleans") && compressor.in_boolean_context()) {
@@ -3034,6 +3044,9 @@ merge(Compressor.prototype, {
})).optimize(compressor);
}
}
if (self.operator == "-" && e instanceof AST_Infinity) {
e = e.transform(compressor);
}
if (e instanceof AST_Binary
&& (self.operator == "+" || self.operator == "-")
&& (e.operator == "*" || e.operator == "/" || e.operator == "%")) {
@@ -3043,8 +3056,7 @@ merge(Compressor.prototype, {
}
// avoids infinite recursion of numerals
if (self.operator != "-"
|| !(self.expression instanceof AST_Number
|| self.expression instanceof AST_Infinity)) {
|| !(e instanceof AST_Number || e instanceof AST_Infinity)) {
var ev = self.evaluate(compressor);
if (ev !== self) {
ev = make_node_from_constant(ev, self).optimize(compressor);
@@ -3087,8 +3099,8 @@ merge(Compressor.prototype, {
OPT(AST_Binary, function(self, compressor){
function reversible() {
return self.left instanceof AST_Constant
|| self.right instanceof AST_Constant
return self.left.is_constant()
|| self.right.is_constant()
|| !self.left.has_side_effects(compressor)
&& !self.right.has_side_effects(compressor);
}
@@ -3101,8 +3113,8 @@ merge(Compressor.prototype, {
}
}
if (commutativeOperators(self.operator)) {
if (self.right instanceof AST_Constant
&& !(self.left instanceof AST_Constant)) {
if (self.right.is_constant()
&& !self.left.is_constant()) {
// if right is a constant, whatever side effects the
// left side might have could not influence the
// result. hence, force switch.
@@ -3464,9 +3476,9 @@ merge(Compressor.prototype, {
case "undefined":
return make_node(AST_Undefined, self).optimize(compressor);
case "NaN":
return make_node(AST_NaN, self);
return make_node(AST_NaN, self).optimize(compressor);
case "Infinity":
return make_node(AST_Infinity, self);
return make_node(AST_Infinity, self).optimize(compressor);
}
}
if (compressor.option("evaluate") && compressor.option("reduce_vars")) {
@@ -3508,7 +3520,38 @@ merge(Compressor.prototype, {
return ref;
}
}
return self;
return make_node(AST_UnaryPrefix, self, {
operator: "void",
expression: make_node(AST_Number, self, {
value: 0
})
});
});
OPT(AST_Infinity, function(self, compressor){
var retain = compressor.option("keep_infinity")
&& !compressor.find_parent(AST_Scope).find_variable("Infinity");
return retain ? self : make_node(AST_Binary, self, {
operator: "/",
left: make_node(AST_Number, self, {
value: 1
}),
right: make_node(AST_Number, self, {
value: 0
})
});
});
OPT(AST_NaN, function(self, compressor){
return compressor.find_parent(AST_Scope).find_variable("NaN") ? make_node(AST_Binary, self, {
operator: "/",
left: make_node(AST_Number, self, {
value: 0
}),
right: make_node(AST_Number, self, {
value: 0
})
}) : self;
});
var ASSIGN_OPS = [ '+', '-', '/', '*', '%', '>>', '<<', '>>>', '|', '^', '&' ];
@@ -3809,7 +3852,7 @@ merge(Compressor.prototype, {
OPT(AST_RegExp, literals_in_boolean_context);
OPT(AST_Return, function(self, compressor){
if (self.value && is_undefined(self.value)) {
if (self.value && is_undefined(self.value, compressor)) {
self.value = null;
}
return self;