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improve collapsible value detection (#1638)

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- #1634 bars variables with cross-scope references in between to collapse
- but if assigned value is side-effect-free, no states can be modified, so it is safe to move
This commit is contained in:
Alex Lam S.L
2017-03-24 02:55:32 +08:00
committed by GitHub
parent 6b2f34769a
commit e918748d88
3 changed files with 73 additions and 3 deletions
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4
lib/compress.js
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@@ -592,9 +592,10 @@ merge(Compressor.prototype, {
// Restrict var replacement to constants if side effects encountered.
if (side_effects_encountered |= lvalues_encountered) continue;
var value_has_side_effects = var_decl.value.has_side_effects(compressor);
// Non-constant single use vars can only be replaced in same scope.
if (ref.scope !== self) {
side_effects_encountered |= var_decl.value.has_side_effects(compressor);
side_effects_encountered |= value_has_side_effects;
continue;
}
@@ -620,6 +621,7 @@ merge(Compressor.prototype, {
|| (parent instanceof AST_If && node !== parent.condition)
|| (parent instanceof AST_Conditional && node !== parent.condition)
|| (node instanceof AST_SymbolRef
&& value_has_side_effects
&& !are_references_in_scope(node.definition(), self))
|| (parent instanceof AST_Binary
&& (parent.operator == "&&" || parent.operator == "||")