More typed arrays in the FrameTable (and a flags column) by mstange · Pull Request #6173 · firefox-devtools/profiler

mstange · 2026-07-13T15:48:30Z

This allows all columns of the frame table to be stored as typed arrays, and reduces the amount of JSON parsing when loading a JSLB profile.

Size profile before: https://share.firefox.dev/469V8zL
Size profile after: https://share.firefox.dev/4ijXlQp

codecov · 2026-07-13T15:50:32Z

Codecov Report

❌ Patch coverage is 90.37975% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.82%. Comparing base (9203f11) to head (7abc8b8).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/profile-logic/bottom-box.ts	0.00%	8 Missing ⚠️
src/profile-logic/merge-compare.ts	68.75%	4 Missing and 1 partial ⚠️
src/profile-logic/symbolication.ts	86.66%	4 Missing ⚠️
src/test/fixtures/profile-summary.ts	55.55%	4 Missing ⚠️
src/profile-logic/js-tracer.ts	83.33%	2 Missing ⚠️
src/profile-logic/line-timings.ts	87.50%	2 Missing ⚠️
src/profile-logic/processed-profile-versioning.ts	95.83%	2 Missing ⚠️
src/profile-logic/profile-compacting.ts	94.87%	1 Missing and 1 partial ⚠️
src/profile-logic/profile-data.ts	96.07%	2 Missing ⚠️
src/profile-query/function-list.ts	0.00%	2 Missing ⚠️
... and 5 more

Additional details and impacted files

@@ Coverage Diff @@## main #6173 +/- ##
==========================================
+ Coverage 83.79% 83.82% +0.02% 
==========================================
Files 350 350 Lines 37583 37744 +161 Branches 10459 10646 +187 ==========================================
+ Hits 31492 31638 +146 - Misses 5664 5677 +13 - Partials 427 429 +2

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canova

Thanks! Looks mostly good to me, but I have a question, it looks like we are changing the old v70 upgrader. Was that intentional?

canova · 2026-08-24T13:30:27Z

+ length,
+ } = frameTable;
+ const flags = new Array<number>(length);
+ for (let i = 0; i < length; i++) {


The following code is pretty hard to read, can we maybe add an inline FrameFlag enum snapshot inside this upgrader?

canova · 2026-08-24T13:32:57Z

+ if (inlineDepth[i] > 0) {
+ f |= 1 << 0;
+ }
+ if (address[i] !== -1 && lib[i] !== null) {


shouldn't this be something like if (address[i] !== -1 && lib[i] !== -1 && lib[i] !== null)? v70 upgrader puts -1 as a "no library" sentinel before this PR. I don't know why we are changing the v70 also, so maybe we don't need null?

Oops. Restored the 70 upgrader and fixed the 71 upgrader to do things properly.

canova · 2026-08-24T13:34:54Z

- // Frames with no library use the sentinel value -1.
 const { frameTable, funcTable, resourceTable } = profile.shared;
- const libForFunc = new Int32Array(funcTable.length).fill(-1);
+ const libForFunc = new Array(funcTable.length).fill(null);
 for (let funcIndex = 0; funcIndex < funcTable.length; funcIndex++) {
 const resourceIndex = funcTable.resource[funcIndex];
 if (resourceIndex !== -1) {
- libForFunc[funcIndex] = resourceTable.lib[resourceIndex] ?? -1;
+ libForFunc[funcIndex] = resourceTable.lib[resourceIndex] ?? null;
 }
 }
- const lib = new Array(frameTable.length).fill(-1);
+ const lib = new Array(frameTable.length).fill(null);


Is this intentional? Why are we changing the older v70 upgrader?

Oops, not intentional.

canova · 2026-08-24T13:37:50Z

+ } else {
+ originalLocation[i] = 0;
+ }
+ flags[i] = f;


I also don't see innerWindowID check for null here. I think we should add it too.

canova · 2026-08-24T13:41:50Z

This commented function is outdated now right? I think we should either remove or update with the new style.

Updated it.

So far, the columns we've converted to typed arrays were either always non-empty, or they used -1 as the "no value" sentinel. For the FrameTable, I've opted to not to use -1 sentinel values, and instead have a flags column with a "HasXYZ" flag for each column (e.g. FrameFlags.HasAddress), for the following reasons: - I'd like to use U8 and U16 arrays for the category and subcategory columns. That's already what we use in the derived StackTable. With an external flag we can go up to 256 subcategories without having to use 16 bits. - I'm changing the inlineDepth column into just a "is inline" bool. This is a good fit for a flag. - The address column was using -1 as the "no address" sentinel; having the flag lets us use U32 instead of I32 for the address column and have relative addresses for 4GiB binaries rather than just 2GiB. An alternative I considered (but discarded) was to have a bitset for each column. E.g. one "isInlined" bitset where, in the JSON, each item is a U8 with the bits for 8 different frames. And similarly we could have a "hasCategory" bitset. But that was too many extra columns in my opinion.

canova

Thanks!

Changes: [Nazım Can Altınova] Update oxfmt 0.59.0 → 0.63.0 (major) (#6262) [Andrew Creskey] Show which network requests were prefetched (#6259) [Florian Quèze] profiler-cli: document the marker field:value search syntax (#6265) [Florian Quèze] profiler-cli: report one time base for text and JSON output (#6266) [Florian Quèze] profiler-cli: avoid a stack overflow on large marker threads (#6264) [Markus Stange] Give the frameTable a lib column (#6258) [Florian Quèze] profiler-cli: accept --limit 0 as unlimited, and make truncation loud (#6267) [Florian Quèze] profiler-cli: report the network request count the filters ran against (#6274) [Nazım Can Altınova] Fix dark mode contrast of the warning icons in the publish panel (#6280) [Nazım Can Altınova] Extract the publish panel warning indicator into a small component (#6282) [Markus Stange] More typed arrays in the FrameTable (and a flags column) (#6173) [Nazım Can Altınova] Improve the profiler-cli publish script and document the whole deployment in a better way (#6260) [fatadel] 🔃 Sync: l10n -> main (September 3, 2026) (#6301) [fatadel] Bump profiler-cli version to 0.9.0 (#6302) And special thanks to our localizers: es-CL: ravmn nl: Mark Heijl sv-SE: Andreas Pettersson sv-SE: Luna Jernberg sv-SE: Peter Kihlstedt tr: Selim Şumlu tr: giray zh-CN: 高乐喆

mstange force-pushed the frametable-flags branch 2 times, most recently from b9ad978 to c49cdaeCompare July 15, 2026 19:22

mstange force-pushed the frametable-flags branch 6 times, most recently from c369b1d to ab6901bCompare August 19, 2026 21:26

mstange requested a review from canova August 19, 2026 21:30

mstange force-pushed the frametable-flags branch from ab6901b to d69ee04Compare August 19, 2026 21:32

mstange marked this pull request as ready for review August 19, 2026 21:35

canova requested changes Aug 24, 2026
View reviewed changes

mstange force-pushed the frametable-flags branch from d69ee04 to 7abc8b8Compare August 25, 2026 14:39

mstange requested a review from canova August 25, 2026 14:44

canova approved these changes Aug 25, 2026
View reviewed changes

mstange merged commit 964fd62 into firefox-devtools:mainAug 25, 2026
23 checks passed

fatadel mentioned this pull request Sep 3, 2026
Deploy September 3, 2026 #6303
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mstange commented Jul 13, 2026•
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