Bugzilla

In JS the RegExp objects are saved globally [here](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/toolkit/components/formautofill/shared/FormAutofillHeuristics.sys.mjs#89) and therefore persisted across runs. They are initialized lazily [here](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/toolkit/components/formautofill/shared/HeuristicsRegExp.sys.mjs#647-673) by overriding the get() property on the first access, then un-overriding it. So the JS code looks correct to me in terms of caching.

For each `FormAutofillChild._doIdentifyAutofillFields()` (which is called when an input element is focused first after page load), we end up calling `testRegex()` a few times per regexp, twice where the input string `hasLatin1Chars()`, and once where it does not. So on the first iteration we compile the regex twice to byte code. For the next 2 and a bit iterations we reuse the cached byte code.

Then we eventually decide the regexp is hot and [decide to tier up](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/js/src/vm/RegExpObject.cpp#618) to jit code. Which means we must recompile
RegExp objects are created when the FormAutofillHeurstics.

In between each iteration [`discardJitCode`](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/js/src/vm/RegExpObject.cpp#584) is called. So once we have tiered up to JIT code, we now must recompile each regexp each iteration.

So perhaps we want to be less eager to call `discardJitCode()`

In JS the RegExp objects are saved globally [here](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/toolkit/components/formautofill/shared/FormAutofillHeuristics.sys.mjs#89) and therefore persisted across runs. They are initialized lazily [here](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/toolkit/components/formautofill/shared/HeuristicsRegExp.sys.mjs#647-673) by overriding the get() property on the first access, then un-overriding it. So the JS code looks correct to me in terms of caching.

For each `FormAutofillChild._doIdentifyAutofillFields()` (which is called when an input element is focused first after page load), we end up calling `testRegex()` a few times per regexp, twice where the input string `hasLatin1Chars()`, and once where it does not. So on the first iteration we compile the regex twice to byte code. For the next 2 and a bit iterations we reuse the cached byte code.

Then we eventually decide the regexp is hot and [decide to tier up](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/js/src/vm/RegExpObject.cpp#618) to jit code. Which means we must recompile.

In between each iteration [`discardJitCode`](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/js/src/vm/RegExpObject.cpp#584) is called. So once we have tiered up to JIT code, we now must recompile each regexp each iteration.

So perhaps we want to be less eager to call `discardJitCode()`

In JS the RegExp objects are saved globally [here](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/toolkit/components/formautofill/shared/FormAutofillHeuristics.sys.mjs#89) and therefore persisted across runs. They are initialized lazily [here](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/toolkit/components/formautofill/shared/HeuristicsRegExp.sys.mjs#647-673) by overriding the get() property on the first access, then un-overriding it. So the JS code looks correct to me in terms of caching.

For each `FormAutofillChild._doIdentifyAutofillFields()` (which is called when an input element is focused first after page load), we end up calling `testRegex()` a few times per regexp, twice where the input string `hasLatin1Chars()`, and once where it does not. So on the first iteration we compile the regex twice to byte code. For the next 2 and a bit iterations we reuse the cached byte code.

Then we eventually decide the regexp is hot and [decide to tier up](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/js/src/vm/RegExpObject.cpp#618) to jit code. Which means we must recompile.

In between each iteration [`discardJitCode()`](https://searchfox.org/mozilla-central/rev/64eef6b342bca86930caf3ba403c0f8ce621b474/js/src/vm/RegExpObject.cpp#584) is called. So once we have tiered up to JIT code, we now must recompile each regexp each iteration.

So perhaps we want to be less eager to call `discardJitCode()`