Bug 159687 – OSR entry into DFG has problems with lexical scoping

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Filip Pizlo]

Patch forthcoming.

[Filip Pizlo]

Created attachment 283448 [details]
the patch

I still need to benchmark this, but I welcome feedback.

[Saam Barati]

Comment on attachment 283448 [details]
the patch

View in context: https://bugs.webkit.org/attachment.cgi?id=283448&action=review

r=me

> Source/JavaScriptCore/ChangeLog:48
> +        This is an enormous speed-up on microbenchmarks that use lexical scoping and have some crazy
> +        put_by_id in the lead-up to the hot loop.

Nice.
Can we convert some other well known benchmark that tiers up in loops to use "let"?

[Filip Pizlo]

(In reply to comment #2)
> Comment on attachment 283448 [details]
> not benchmarked patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=283448&action=review
> 
> r=me
> 
> > Source/JavaScriptCore/ChangeLog:48
> > +        This is an enormous speed-up on microbenchmarks that use lexical scoping and have some crazy
> > +        put_by_id in the lead-up to the hot loop.
> 
> Nice.
> Can we convert some other well known benchmark that tiers up in loops to use
> "let"?

We could but not all users of OSR entry need this particular mitigation, and I don't remember which ones do.  The microbenchmark attached to this patch seems pretty good though!  It precisely illustrates the issue in tip of tree.

[Filip Pizlo]

Created attachment 283459 [details]
performance

[Filip Pizlo]

Comment on attachment 283448 [details]
the patch

Benchmarks show perf neutrality, except for the strict-osr-entry microbenchmark, which speeds up a ton.

[Filip Pizlo]

Landed in https://trac.webkit.org/changeset/203356