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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - NewRegexp should not prevent inlining"
href="https://bugs.webkit.org/show_bug.cgi?id=154808#c10">Comment # 10</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - NewRegexp should not prevent inlining"
href="https://bugs.webkit.org/show_bug.cgi?id=154808">bug 154808</a>
from <span class="vcard"><a class="email" href="mailto:fpizlo@apple.com" title="Filip Pizlo <fpizlo@apple.com>"> <span class="fn">Filip Pizlo</span></a>
</span></b>
<pre>(In reply to <a href="show_bug.cgi?id=154808#c9">comment #9</a>)
<span class="quote">> (In reply to <a href="show_bug.cgi?id=154808#c8">comment #8</a>)
> > Comment on <span class=""><a href="attachment.cgi?id=286601&action=diff" name="attach_286601" title="Patch">attachment 286601</a> <a href="attachment.cgi?id=286601&action=edit" title="Patch">[details]</a></span>
> > Patch
> >
> > You shouldn't be adding any new fields to CodeBlock.
> >
> > The DFG already has a mechanism for strongly marking objects known to the
> > compiler such as the RegExps. It's called freezing: just do
> > m_graph.freezeStrongly(...).
> >
> > You don't need to record the RegExp object anywhere other than the NewRegExp
> > node. That node should not have an index into any vectors. It should just
> > hold a pointer to RegExp. We already do this for other node types. See for
> > example Node::cellOperand(). Notice that its already compatible with
> > freezing.
>
> Thank you for this info. I really didn't know about that. I took a look in
> code using the freezing and it looks simpler and more correct than my
> current patch. Just for curiosity, as I understood, this Freeze mechanism
> interact with the GC, right? If yes, How does it happen?</span >
There's a lot of logic there:
- Freezing causes the resulting CodeBlock to have either a strong or weak reference to the frozen object, depending on whether you froze it strongly or weakly.
- Freezing immediately causes the ongoing DFG compilation plan to track the reference if a GC happens while the compiler is running. The GC knows how to safepoint the compiler. This means that from the compiler's standpoint, GCs can only happen at well-defined points: either before the compiler started, during B3 compilation, or after the compiler finished.
There are a lot of other details; I can't remember all of them off the top of my head. The short version is just: we already use freezing a lot, and it's designed exactly for what you want: you have some object that the generated code will refer to and you want to make sure that this object gets marked.</pre>
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