This is a great idea! - Joe
> On Jan 13, 2020, at 5:52 PM, Yusuke Suzuki <ysuz...@apple.com> wrote: > > Hello WebKittens, > > I recently striped 830KB binary size in WebKit just by using a work-around. > This email describes what happened so far, to prevent from happening again. > > ## Problem > > When C/C++ struct/class is included in field types and method types in > Objective-C, Objective-C compiler puts type-enconding-string which gathers > type information one-leve deep for C/C++ struct/class if > > 1. The type is a pointer to C/C++ struct/class > 2. The type is a value of C/C++ struct/class > 3. The type is a reference to C/C++ struct/class > > However, our WebKit C/C++ struct/class is typically very complex type using a > lot of templates. Unfortunately, Objective-C compiler includes expanded > template definition as a string and adds it as a type-enconding-string into > the release binary! > > For example, https://trac.webkit.org/changeset/254152/webkit > <https://trac.webkit.org/changeset/254152/webkit> is removing JSC::VM& from > Objective-C signature, and it reduces 200KB binary size! > Another example is https://trac.webkit.org/changeset/254241/webkit > <https://trac.webkit.org/changeset/254241/webkit>, which removes a lot of > WebCore::WebView* etc. from Objective-C method signature, and reduces 630KB > binary. > > ## Solution for now > > We can purge type-encoding-string if we use Objective-C NS_DIRECT feature > (which makes Objective-C function as C function calling convention, removing > metadata). > However, this does not work universally: with NS_DIRECT, Objective-C override > does not work. This means we need to be extra-careful when using it. > > So, as a simple, but effective work-around, in the above patch, we introduced > NakedRef<T> / NakedPtr<T>. This is basically raw pointer / raw reference to > T, with a wrapper class. > This leverages the behavior of Objective-C compiler’s mechanism “one-level > deep type information collection”. Since NakedRef<T> / NakedPtr<T> introduces > one-level deep field, > Objective-C compiler does not collect the type information of T if > NakedPtr<T> is included in the fields / signatures, while the compiler > collects information when T* is used. > > So, if you are using T& / T* C/C++ struct/class in Objective-C, let’s convert > it to NakedRef<T> / NakedPtr<T>. Then you could save much binary size > immediately without causing any performance problem. > > ## Future work > > We would like to avoid including such types accidentally in Objective-C. We > should introduce build-time hook script which detects such a thing. > I uploaded the PoC script in https://bugs.webkit.org/show_bug.cgi?id=205968 > <https://bugs.webkit.org/show_bug.cgi?id=205968>, and I’m personally planning > to introduce such a hook into a part of build process. > > > -Yusuke > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev
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