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enhance if_return (#2703)

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This commit is contained in:
Alex Lam S.L
2018-01-02 15:09:51 +08:00
committed by GitHub
parent d838b4b52e
commit cc931b3ad8
2 changed files with 86 additions and 14 deletions
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54
lib/compress.js
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@@ -1343,12 +1343,13 @@ merge(Compressor.prototype, {
var in_lambda = self instanceof AST_Lambda;
for (var i = statements.length; --i >= 0;) {
var stat = statements[i];
var next = statements[i + 1];
var j = next_index(i);
var next = statements[j];
if (in_lambda && !next && stat instanceof AST_Return) {
if (!stat.value) {
CHANGED = true;
statements.length--;
statements.splice(i, 1);
continue;
}
if (stat.value instanceof AST_UnaryPrefix && stat.value.operator == "void") {
@@ -1418,7 +1419,8 @@ merge(Compressor.prototype, {
CHANGED = true;
stat = stat.clone();
stat.alternative = next;
statements.splice(i, 2, stat.transform(compressor));
statements.splice(i, 1, stat.transform(compressor));
statements.splice(j, 1);
continue;
}
//---
@@ -1430,7 +1432,8 @@ merge(Compressor.prototype, {
stat.alternative = next || make_node(AST_Return, stat, {
value: null
});
statements.splice(i, next ? 2 : 1, stat.transform(compressor));
statements.splice(i, 1, stat.transform(compressor));
if (next) statements.splice(j, 1);
continue;
}
//---
@@ -1439,10 +1442,10 @@ merge(Compressor.prototype, {
// if sequences is not enabled, this can lead to an endless loop (issue #866).
// however, with sequences on this helps producing slightly better output for
// the example code.
var prev = statements[i - 1];
var prev = statements[prev_index(i)];
if (compressor.option("sequences") && in_lambda && !stat.alternative
&& prev instanceof AST_If && prev.body instanceof AST_Return
&& i + 2 == statements.length && next instanceof AST_SimpleStatement) {
&& next_index(j) == statements.length && next instanceof AST_SimpleStatement) {
CHANGED = true;
stat = stat.clone();
stat.alternative = make_node(AST_BlockStatement, next, {
@@ -1453,7 +1456,8 @@ merge(Compressor.prototype, {
})
]
});
statements.splice(i, 2, stat.transform(compressor));
statements.splice(i, 1, stat.transform(compressor));
statements.splice(j, 1);
continue;
}
}
@@ -1503,6 +1507,26 @@ merge(Compressor.prototype, {
}
return body;
}
function next_index(i) {
for (var j = i + 1, len = statements.length; j < len; j++) {
var stat = statements[j];
if (!(stat instanceof AST_Definitions && declarations_only(stat))) {
break;
}
}
return j;
}
function prev_index(i) {
for (var j = i; --j >= 0;) {
var stat = statements[j];
if (!(stat instanceof AST_Definitions && declarations_only(stat))) {
break;
}
}
return j;
}
}
function eliminate_dead_code(statements, compressor) {
@@ -1575,19 +1599,17 @@ merge(Compressor.prototype, {
function to_simple_statement(block, decls) {
if (!(block instanceof AST_BlockStatement)) return block;
var defs = [];
var stat = null;
for (var i = 0, len = block.body.length; i < len; i++) {
var line = block.body[i];
if (line instanceof AST_Definitions && declarations_only(line)) {
defs.push(line);
decls.push(line);
} else if (stat) {
return false;
} else {
stat = line;
}
}
[].push.apply(decls, defs);
return stat;
}
@@ -1599,7 +1621,7 @@ merge(Compressor.prototype, {
return make_sequence(left, [ left, right ]).transform(compressor);
};
var n = 0, prev;
for (var i = 0, len = statements.length; i < len; i++) {
for (var i = 0; i < statements.length; i++) {
var stat = statements[i];
if (prev) {
if (stat instanceof AST_For && !(stat.init instanceof AST_Definitions)) {
@@ -1641,15 +1663,19 @@ merge(Compressor.prototype, {
var body = to_simple_statement(stat.body, decls);
var alt = to_simple_statement(stat.alternative, decls);
if (body !== false && alt !== false && decls.length > 0) {
var len = decls.length;
decls.push(make_node(AST_If, stat, {
condition: stat.condition,
body: body || make_node(AST_EmptyStatement, stat.body),
alternative: alt
}));
stat = make_node(AST_BlockStatement, stat, {
body: decls
});
decls.unshift(n, 1);
[].splice.apply(statements, decls);
i += len;
n += len + 1;
prev = null;
CHANGED = true;
continue;
}
}
statements[n++] = stat;