Re: [gentoo-user] Re: sys-devel/llvm and LLVM_TARGETS

[Wols Lists]

On 12/03/2022 14:22, Nikos Chantziaras wrote:
> On 12/03/2022 10:43, Dale wrote:
>> https://bugs.gentoo.org/767700
>>
>> Is that the one?  It mentions the target but I don't quite understand
>> the why.  The biggest thing, will this break something if I let it do
>> it?
>
> No. Unlike GCC, LLVM/Clang is always a cross-compiler. This just enables
> some extra targets. It won't actually affect anything other than perhaps
> the binaries becoming a bit larger.
>
>
I don't fully understand it (and I thought gcc was moving in the same 
direction), but Clang is a front-end, compiling C to "Intermediate 
Representation". LLVM is a middle/back end which calls optimisation 
modules on the IR which finally end up spitting out machine code - for 
whatever definition of machine code floats your boat.

So I guess adding these extra targets just adds another LLVM module that 
just happens to spit out these extra different machine codes.

But that's how LLVM can compile so many different languages - it simply 
converts IR to machine code. There's a whole bunch of different front 
ends, it's just that Clang is the most well known because the world and 
his dog work in C/C++. I believe there's a rust front end, amongst 
others, but it feels like other languages are a bit "second class". Not 
intentionally, but the C guys have so much input into the IR that the 
other languages get swamped, and people take a while to realise that 
what was a good decision for C was not a good decision for languages in 
general, and the other guys are playing catch-up because nobody noticed.

That's not a dig at anybody, it's just life.

I used to follow this on the LLVM mailing list, but that's now migrated 
to discourse, and I think I'm amongst a lot of people who didn't follow 
it ...

Cheers,
Wol