[Libre-soc-bugs] [Bug 1229] fosdem2024 llvm simple-v

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1229

--- Comment #6 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #4)
> > for LLVM IR, we will be having standard existing vector IR translate to
> > SimpleV ops in the backend, not something like having only SimpleV prefixed
> > IR and never any vector ops or something like that.
> 
> ... i then envisage an IR primitive that LITERALLY and precisely
> without fail without exception represents the FULL and complete
> capability of SV Prefixing. exactly precisely fully absolute
> 100% without fail absolute total and full representation of
> the full absolute SV concept.

fine with me, though I imagine you will have a tough time convincing gcc/llvm
maintainers to redo their IR...

> no vector instructions =>
> no vector IR.

we *need* vector IR support (supporting *already existing LLVM IR*) because it
allows existing vector code to compile to SimpleV without having to rewrite all
software everywhere. Also, all of LLVM's existing optimization pipelines and
everything else all uses vector IR, trying to force everyone to use only
SimpleV IR to get anything beyond scalar performance is going to make SimpleV
fail, because we're currently the little dog and most programmers don't care
about SimpleV and will just use stuff that makes vector IR regardless.

Remember, supporting existing vector LLVM IR is similar to supporting existing
PowerPC software or to supporting existing C software, we care about backward
compatibility because we *can't* rewrite the world.

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