> 2) slower code: most of the time the indirection through a pointer variable (the state) in comparison to a direct access to a static variable doesn't matter.
In fact, I experimented the opposite. When moving all global variables to a struct, my Lisp was around 1% faster because globals are now close together and more often accessible from L1 cache. It has of course no effect when global is a pointer which introduces the same indirection. It is true for aggressive optimizers which are likely to put struct pointer to a register. So it may be faster for tcc compiled by gcc, clang or vc++ but slower when tcc is compiled by tcc. C. -----Original Message----- From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=orange...@nongnu.org] On Behalf Of Michael Matz Sent: Friday, December 06, 2019 16:42 To: TCC mailing list Subject: Re: [Tinycc-devel] make tcc reentrant Hello, On Tue, 3 Dec 2019, Ulrich Schmidt wrote: > i try to write a lua binding for tcc. To work out propperly, the tcc lib > needs to be reentrant. As demonstrated down-thread, that isn't correct. It doesn't _need_ to be, it would be an feature. As usual with features it needs to be measured against the downsides. The downsides for your proposed changes are the following at least: 1) more complicated/boiler-platy source code of TCC (a TCCState argument almost everywhere) 2) slower code: most of the time the indirection through a pointer variable (the state) in comparison to a direct access to a static variable doesn't matter. But it does matter for the symbol/token table (and potentially for the register/evaluation stack). I have measured this years ago for the token table, so this might or might not still be the case. So, while I can see the wish for this feature, I don't necessarily see that tcc should be changed to accomodate. If anything I would expect a _complete_ transition to exist, in order to measure the impact. The worst thing that could happen is if someone added TCCState arguments everywhere, moved some static variables to that state, and then leaves: none of the features of this whole excercise would be had, but all the downsides would be there. And yes, this is a big project. I really think it would be better if you simply write a wrapper for libtcc that ensures single-threadedness and that regards TCCState as a singleton. I think such thing would be well-suited in the TCC sources itself. (In a way it seems prudent for a tiny C compiler to only be usable as a singleton) Ciao, Michael. > > I took a look into the sources and found some comments (XXX:...) and > started with removing > > the static var tcc_state. As a result allmost all lib functions needs a > 1st parameter of > > type TCCState*. I did this in my own local branch and tcc is still > running :). > > But this is a really HUGE change. in addition most of the local vars in > tccpp, tccgen, ... needs > > to be moved to TCCState. I can do that but at some points i will have > some questions and i > > can only test on windows and probably on linux. > > My 1st question is: Are you interested in these changes or should i do > this locally? > > I would like to this together with you. > > > Greetings. > > Ulrich. > > > _______________________________________________ > Tinycc-devel mailing list > Tinycc-devel@nongnu.org > https://lists.nongnu.org/mailman/listinfo/tinycc-devel > _______________________________________________ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel _______________________________________________ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
