Fix exponential compilation blowup in pattern matching and boolean si…#8078
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cristianoc merged 1 commit intomasterfrom Dec 9, 2025
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Fix exponential compilation blowup in pattern matching and boolean si…#8078cristianoc merged 1 commit intomasterfrom
cristianoc merged 1 commit intomasterfrom
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…mplification This PR fixes two sources of exponential compilation time: 1. **Boolean expression simplification** (`js_exp_make.ml`): The `simplify_and_` function had O(3^n) recursive behavior when simplifying nested AND expressions. Added a depth limit (10) to prevent exponential blowup while preserving optimizations for normal cases. Fixes the issue reported in #8039 and #8042 (large unboxed variants). Note: PR #8039's diagnosis of "infinite recursion" was incorrect - the actual issue was exponential blowup, not infinite loops. 2. **Exhaustiveness checking** (`parmatch.ml`): The `exhaust_gadt` function had exponential complexity (~4^n) when checking exhaustiveness for dict pattern matching. Added a call count limit (1000) that conservatively reports non-exhaustive when exceeded, preventing hangs while maintaining correctness. Performance improvements: - Large unboxed variants (28 cases): 3.79s -> 0.03s (126x faster) - Dict pattern matching (6 cases): 0.94s -> 0.04s (24x faster) Added test cases for both scenarios. Closes #8074 Closes #8039 Closes #8042
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This lead to some unfortunate output when upgrading: For k->Context.onKeyRelease(key => {
switch key {
| Space => fly(bird)
| _ => ()
}
})I now get: k.onKeyRelease(key => {
if ((key === "f6" || key === " " || key === "f7" || key === "space" || key === "f8" || key === "meta" || key === "f9" || key === "alt" || key === "f10" || key === "control" || key === "f11" || key === "tab" || key === "f12" || key === "enter" || key === "`" || key === "backspace" || key === "1" || key === "escape" || key === "2" || key === "/" || key === "3" || key === "." || key === "4" || key === "," || key === "5" || key === "m" || key === "6" || key === "n" || key === "7" || key === "b" || key === "8" || key === "v" || key === "9" || key === "c" || key === "0" || key === "x" || key === "-" || key === "z" || key === "+" || key === "'" || key === "=" || key === ";" || key === "q" || key === "l" || key === "w" || key === "k" || key === "e" || key === "j" || key === "r" || key === "h" || key === "t" || key === "g" || key === "y" || key === "f" || key === "u" || key === "d" || key === "i" || key === "s" || key === "o" || key === "a" || key === "p" || key === "\\" || key === "[" || key === "]") && key === "space") {
return fly(bird);
}
});where I had: k.onKeyRelease(key => {
if (key === "space") {
return fly(bird);
}
});and |
Collaborator
Author
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My motivation for looking into this further has decreases as the bug reports from users have been fixed. |
Member
|
Fair enough |
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…mplification
This PR fixes two sources of exponential compilation time:
Boolean expression simplification (
js_exp_make.ml): Thesimplify_and_function had O(3^n) recursive behavior when simplifying nested AND expressions. Added a depth limit (10) to prevent exponential blowup while preserving optimizations for normal cases.Fixes the issue reported in Fix infinite recursion in E.econd when optimizing nested conditionals #8039 and repro large variant timeout #8042 (large unboxed variants). Note: PR Fix infinite recursion in E.econd when optimizing nested conditionals #8039's diagnosis of "infinite recursion" was incorrect - the actual issue was exponential blowup, not infinite loops.
Exhaustiveness checking (
parmatch.ml): Theexhaust_gadtfunction had exponential complexity (~4^n) when checking exhaustiveness for dict pattern matching. Added a call count limit (1000) that conservatively reports non-exhaustive when exceeded, preventing hangs while maintaining correctness.Performance improvements:
Added test cases for both scenarios.
Closes #8074
Closes #8039
Closes #8042