Bug 226149

Summary: Use singleton thunks for virtual calls.
Product: WebKit Reporter: Mark Lam <mark.lam>
Component: JavaScriptCoreAssignee: Mark Lam <mark.lam>
Status: RESOLVED FIXED    
Severity: Normal CC: ews-watchlist, keith_miller, msaboff, saam, tzagallo, webkit-bug-importer, ysuzuki
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   
Attachments:
Description Flags
proposed patch.
ews-feeder: commit-queue-
proposed patch. ysuzuki: review+, ews-feeder: commit-queue-

Description Mark Lam 2021-05-22 18:02:26 PDT 
The pre-existing implementation emits a unique thunk for each virtual call site.  This turns out to be very wasteful in terms of memory.  For example, Speedometer2 ends up generating ~16M of virtualFor thunks.  Switching to re-useable singleton thunks, saves that 16M, and also appears to improve Speedometer2 performance by 1.012x.
Comment 1 Radar WebKit Bug Importer 2021-05-22 18:02:55 PDT 
<rdar://problem/78357604>
Comment 2 Mark Lam 2021-05-22 18:03:41 PDT 
Forgot to say, the 1.012x was measured on a M1 Mac.
Comment 3 Mark Lam 2021-05-22 18:21:53 PDT 
Created attachment 429445 [details]
proposed patch.

Let's try this on the EWS.
Comment 4 Mark Lam 2021-05-22 21:55:42 PDT 
Created attachment 429457 [details]
proposed patch.
Comment 5 Yusuke Suzuki 2021-05-22 22:32:15 PDT 
Comment on attachment 429457 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=429457&action=review

r=me

> Source/JavaScriptCore/ChangeLog:13
> +        2. Introduce Options::useUniqueVirtualThunks() to allow unique thunks to be
> +           generated for testing and comparisons.  Options::useUniqueVirtualThunks() is
> +           false by default.

Maybe this flag is not necessary.

> Source/JavaScriptCore/jit/ThunkGenerators.cpp:275
> +    bool isTailCall = (mode == CallMode::Tail);

() is not necessary.
Comment 6 Mark Lam 2021-05-22 23:02:45 PDT 
Comment on attachment 429457 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=429457&action=review

>> Source/JavaScriptCore/ChangeLog:13
>> +           false by default.
> 
> Maybe this flag is not necessary.

I suppose we can always add it later if a need arises.  I'll remove it.

>> Source/JavaScriptCore/jit/ThunkGenerators.cpp:275
>> +    bool isTailCall = (mode == CallMode::Tail);
> 
> () is not necessary.

Will fix.
Comment 7 Mark Lam 2021-05-22 23:24:30 PDT 
Thanks for the review.  Landed in r277929: <http://trac.webkit.org/r277929>.