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enhance reduce_vars & unused (#4890)

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This commit is contained in:
Alex Lam S.L
2021-05-01 17:19:56 +01:00
committed by GitHub
parent 16411dcb87
commit 53b57ee57e
3 changed files with 184 additions and 16 deletions
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26
lib/compress.js
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@@ -610,6 +610,11 @@ merge(Compressor.prototype, {
function is_immutable(value) {
if (!value) return false;
if (value instanceof AST_Assign) {
var op = value.operator;
return op == "=" ? is_immutable(value.right) : !lazy_op[op.slice(0, -1)];
}
if (value instanceof AST_Sequence) return is_immutable(value.tail_node());
return value.is_constant() || is_lambda(value) || value instanceof AST_ObjectIdentity;
}
@@ -901,6 +906,7 @@ merge(Compressor.prototype, {
function walk_assign() {
right.walk(tw);
var modified = is_modified(compressor, tw, node, right, 0, is_immutable(right), recursive_ref(tw, d));
scan_declaration(tw, compressor, left, function() {
return node.right;
}, function(sym, fixed, walk) {
@@ -911,10 +917,7 @@ merge(Compressor.prototype, {
}
var d = sym.definition();
d.assignments++;
if (fixed
&& !is_modified(compressor, tw, node, right, 0, is_immutable(right), recursive_ref(tw, d))
&& !sym.in_arg
&& safe_to_assign(tw, d)) {
if (fixed && !modified && !sym.in_arg && safe_to_assign(tw, d)) {
push_ref(d, sym);
mark(tw, d);
if (d.single_use && left instanceof AST_Destructured) d.single_use = false;
@@ -6299,18 +6302,13 @@ merge(Compressor.prototype, {
var drop_sym = is_var ? can_drop_symbol(def.name) : is_safe_lexical(sym);
if (!drop_sym || !drop_vars || sym.id in in_use_ids) {
if (value && indexOf_assign(sym, def) < 0) {
var write_only = value.write_only;
value = value.drop_side_effect_free(compressor);
if (def.value !== value) {
if (value) {
AST_Node.warn("Side effects in last use of variable {name} [{file}:{line},{col}]", template(def.name));
side_effects.push(value);
}
value = null;
trim_defns.push(def);
} else if (value.write_only !== write_only) {
value.write_only = write_only;
if (value) {
AST_Node.warn("Side effects in last use of variable {name} [{file}:{line},{col}]", template(def.name));
side_effects.push(value);
}
value = null;
trim_defns.push(def);
}
var old_def;
if (!value && !(node instanceof AST_Let)) {