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improve compression of if conditions (#2544)

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This commit is contained in:
Alex Lam S.L
2017-12-01 06:18:31 +08:00
committed by GitHub
parent b762f2d6f4
commit 5a1e99d713
6 changed files with 60 additions and 22 deletions
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44
lib/compress.js
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@@ -3147,28 +3147,34 @@ merge(Compressor.prototype, {
// “has no side effects”; also it doesn't work for cases like
// `x && true`, though it probably should.
var cond = self.condition.evaluate(compressor);
if (cond !== self.condition) {
if (cond) {
compressor.warn("Condition always true [{file}:{line},{col}]", self.condition.start);
if (compressor.option("dead_code")) {
var a = [];
if (self.alternative) {
extract_declarations_from_unreachable_code(compressor, self.alternative, a);
}
a.push(self.body);
return make_node(AST_BlockStatement, self, { body: a }).optimize(compressor);
}
} else {
if (!compressor.option("dead_code") && !(cond instanceof AST_Node)) {
var orig = self.condition;
self.condition = make_node_from_constant(cond, orig);
self.condition = best_of_expression(self.condition.transform(compressor), orig);
}
if (compressor.option("dead_code")) {
if (cond instanceof AST_Node) cond = self.condition.tail_node().evaluate(compressor);
if (!cond) {
compressor.warn("Condition always false [{file}:{line},{col}]", self.condition.start);
if (compressor.option("dead_code")) {
var a = [];
extract_declarations_from_unreachable_code(compressor, self.body, a);
if (self.alternative) a.push(self.alternative);
return make_node(AST_BlockStatement, self, { body: a }).optimize(compressor);
var body = [];
extract_declarations_from_unreachable_code(compressor, self.body, body);
body.push(make_node(AST_SimpleStatement, self.condition, {
body: self.condition
}));
if (self.alternative) body.push(self.alternative);
return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
} else if (!(cond instanceof AST_Node)) {
compressor.warn("Condition always true [{file}:{line},{col}]", self.condition.start);
var body = [];
if (self.alternative) {
extract_declarations_from_unreachable_code(compressor, self.alternative, body);
}
body.push(make_node(AST_SimpleStatement, self.condition, {
body: self.condition
}));
body.push(self.body);
return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
}
cond = make_node_from_constant(cond, self.condition).transform(compressor);
self.condition = best_of_expression(cond, self.condition);
}
var negated = self.condition.negate(compressor);
var self_condition_length = self.condition.print_to_string().length;