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Rust GCC backend: Why and how

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Re: Rust GCC backend: Why and how

#11

Post by wahern »

ayende wrote: post #3
MangoToupe wrote: post #2

I find it shocking that 20 years after LLVM was created, gcc still hasn't moved towards modularization of codegen.

Isn't that very much intentional on the part of GCC?

Not anymore. Modularization is somewhat tangential, but for awhile Stallman did actively oppose rearchitecting GCC to better support non-free plugins and front-ends. But Stallman lost that battle years ago. AFAIU, the current state of GCC is the result of intentional technical choices (certain kinds of decoupling not as beneficial as people might think--Rust has often been stymied by lack of features in LLVM, i.e. defacto (semantic?) coupling), works in progress (decoupling ongoing), or lack of time or wherewithal to commit to certain major changes (decoupling too onerous).

Re: Rust GCC backend: Why and how

#12

Post by pjmlp »

MangoToupe wrote: post #2

I find it shocking that 20 years after LLVM was created, gcc still hasn't moved towards modularization of codegen.

LLVM wasn't the first modularization of codegen, see Amsterdam Compiler Kit for prior art, among others.

GCC approach is on purpose, plus even if they wanted to change, who would take the effort to make existing C, C++, Objective-C, Objective-C++, Fortran, Modula-2, Algol 68, Ada, D, and Go frontends adopt the new architecture?

Even clang with all the LLVM modularization is going to take a couple of years to move from plain LLVM IR into MLIR dialect for C based languages, https://github.com/llvm/clangir

Re: Rust GCC backend: Why and how

#14

Post by bigfishrunning »

colechristensen wrote: post #8
colejohnson66 wrote: post #5

Earlier quoted context omitted.

Somewhat. Stallman claims to have tried to make it modular,[0] but also that he wants to avoid "misuse of [the] front ends".[1] The idea is that you should link the front and back ends, to prevent out-of-process GPL runarounds. But because of that, the mingling of the front and back ends ended up winning out over attempts to stay modular. [0]: https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00... [1]: https…

Good lord Stallman is such a zealot and hypocrite. It's not open vs. closed it's mine vs. yours and he's openly declaring that he's nerfing software in order to prevent people from using it in a way he doesn't like. And refusing to talk about it in public because normal people hate that shit "misunderstanding" him. --- From the post: I let this drop back in March -- please forgive me. > Maybe that's the issue for GCC…

He should just re-license GCC to close whatever perceived loophole, instead of actively making GCC more difficult to work with (for everyone!). RMS has done so much good, but he's so far from an ideal figure.

Re: Rust GCC backend: Why and how

#15

Post by Croak »

colejohnson66 wrote: post #5
ayende wrote: post #3

Earlier quoted context omitted.

Isn't that very much intentional on the part of GCC?

Somewhat. Stallman claims to have tried to make it modular,[0] but also that he wants to avoid "misuse of [the] front ends".[1] The idea is that you should link the front and back ends, to prevent out-of-process GPL runarounds. But because of that, the mingling of the front and back ends ended up winning out over attempts to stay modular. [0]: https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00... [1]: https…

When gcc was built most compilers were proprietary. Stallman wanted a free compiler and to keep it free. The GPL license is more restrictive, but it's philosophy is clear. At the end of the day the code's writer can choose if and how people are allowed to use it. You don't have to use it, you can use something else or build you own. And maybe, just maybe Linux is thriving while Windows is dying because in the Linux ecosystem everybody works together and shares, while in Windows everybody helps together paying for Satya Nadellas next yacht.

Re: Rust GCC backend: Why and how

#16

Post by mastax »

> On that note: GCC doesn't provide a nice library to give access to its internals (unlike LLVM). So we have to use libgccjit which, unlike the "jit" ("just in time", meaning compiling sub-parts of the code on the fly, only when needed for performance reasons and often used in script languages like Javascript) part in its name implies, can be used as "aot" ("ahead of time", meaning you compile everything at once, allowing you to spend more time on optimization).

Is libgccjit not “a nice library to give access to its internals?”

Re: Rust GCC backend: Why and how

#17

Post by saghm »

mastax wrote: post #16

> On that note: GCC doesn't provide a nice library to give access to its internals (unlike LLVM). So we have to use libgccjit which, unlike the "jit" ("just in time", meaning compiling sub-parts of the code on the fly, only when needed for performance reasons and often used in script languages like Javascript) part in its name implies, can be used as "aot" ("ahead of time", meaning you compile everything at once, all…

I could be wrong, but my surface level understanding is that it's more of a library version of the external API of GCC than one that gives access to the internals.

Re: Rust GCC backend: Why and how

#18

Post by torginus »

wahern wrote: post #11
ayende wrote: post #3

Earlier quoted context omitted.

Isn't that very much intentional on the part of GCC?

Not anymore. Modularization is somewhat tangential, but for awhile Stallman did actively oppose rearchitecting GCC to better support non-free plugins and front-ends. But Stallman lost that battle years ago. AFAIU, the current state of GCC is the result of intentional technical choices (certain kinds of decoupling not as beneficial as people might think--Rust has often been stymied by lack of features in LLVM, i.e. de…

Personally, I think when you are making bad technical decisions in service of legal goals (making it harder to circumvent the GPL), that's a sure sign that you made a wrong turn somewhere.

Re: Rust GCC backend: Why and how

#20

Post by 1718627440 »

MangoToupe wrote: post #2

I find it shocking that 20 years after LLVM was created, gcc still hasn't moved towards modularization of codegen.

It is a political not a technical decision. Essentially the same like the Linux kernel not encouraging the use of out-of-tree kernel modules. https://gcc.gnu.org/legacy-ml/gcc/2000-01/msg00572.html
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