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Ensure switch branches reordering happens only for constant branch expressions #1092

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merged 1 commit into from Oct 19, 2021
Merged

Ensure switch branches reordering happens only for constant branch expressions #1092

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2 changes: 1 addition & 1 deletion lib/compress/index.js
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Expand Up @@ -1606,7 +1606,7 @@ def_optimize(AST_Switch, function(self, compressor) {
// that way the next micro-optimization will merge them.
// ** bail micro-optimization if not a simple switch case with breaks
if (body.every((branch, i) =>
(branch === default_or_exact || !branch.expression.has_side_effects(compressor))
(branch === default_or_exact || branch.expression instanceof AST_Constant)
&& (branch.body.length === 0 || aborts(branch) || body.length - 1 === i))
) {
for (let i = 0; i < body.length; i++) {
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36 changes: 36 additions & 0 deletions test/compress/switch.js
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Expand Up @@ -2594,6 +2594,42 @@ collapse_same_branches_not_in_a_row_ensure_no_side_effects: {
}
expect_stdout: ["2"]
}

collapse_same_branches_not_in_a_row_ensure_no_evaluate_elad: {
options = {
switches: true,
dead_code: true
}
input: {
let i = 1;
switch (true) {
case 3 == i:
console.log(i);
break;
case 5 == i:
console.log(5);
break;
case 1 == i:
console.log(i);
break;
Comment on lines +2606 to +2614
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Nit: I'm not sure this properly catches the bug (but the output isn't optimized, so it's not a hard blocker). We need to test that non-mutually-exclusive branches are correct:

Suggested change
case 3 == i:
console.log(i);
break;
case 5 == i:
console.log(5);
break;
case 1 == i:
console.log(i);
break;
case 3 == i:
console.log('equals');
break;
case 5 > i:
console.log('greater than');
break;
case 1 == i:
console.log('equals');
break;

This case should log 'greater than', but if we did the optimization, it would log equals (because the 1 == i would have been moved up).

}
}
expect: {
let i = 1;
switch (true) {
case 3 == i:
console.log(i);
break;
case 5 == i:
console.log(5);
break;
case 1 == i:
console.log(i);
}
}
expect_stdout: ["1"]
}

collapse_same_branches_not_in_a_row_even_if_last_case_without_abort: {
options = {
switches: true,
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