[llvm-dev] [GlobalISel] Quick Status

[Sean Silva via llvm-dev]

Hi Quentin,

My understanding is that throughout the GISel lowering process all the
lowering steps use the same underlying MI representation, but have
different invariants at different points in time (for example, G_ opcodes
may be present at some point but it would be an "assert" failure to see
them at other points). Are there currently any plans (or things already
implemented) to verify that these invariants hold at different points
throughout the lowering pipeline? Also, in order to run passes in
isolation, ideally they would have nice, easily-understandable failure
modes if you feed them MIR with invariants they don't expect.

The reason I bring this up is that at work I'm currently working on a
compiler (not llvm-based) which does its lowering on a single IR and this
is one of the most consistent pain points. In LLVM we already have this
problem in the form of e.g. pre-RA and post-RA MI, but it seems like GISel
is going to magnify this significantly.


-- Sean Silva

On Fri, Jan 20, 2017 at 5:19 PM, Quentin Colombet via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi all,
>
> Following the thread from http://lists.llvm.org/pipermail/llvm-dev/2017-
> January/109029.html, I am sending this email to give a status on
> GlobalISel progress and situation.
>
> We are pushing GlobalISel from the state of prototype to a production
> quality framework. We welcome help with patches, reviews, feedbacks and so
> on.
>
> As explained during the last developer meeting, we are aiming at enabling
> GISel by default for AArch64 at -O0 for this year (See
> http://llvm.org/devmtg/2016-11/#talk16).
>
> Note: That does not mean the design is settle nor that we won’t change the
> APIs.
> Note: A lot of the things listed in this email is a reminder of what we
> said during the dev meeting talk.
>
> *** High Level View ***
>
> As of r292481, we compile and run correctly with GISel (without fall back
> to SDISel) 63% of the LLVM test suite. If you are interested in detailed
> numbers, please see the attachments (courtesy of Kristof Beyls).
>
> Note: The compile time numbers are probably noisy (compiled in parallel on
> the same machine), and not relevant at this point of the project anyway.
>
>
> *** Per Pass Status ***
>
> ** IRTranslator **
>
> Mostly done.
>
> * What’s Left? *
>
> Some instructions are not yet supported.
>
>
> ** Legalizer **
>
> Core logic is present.
>
> * What’s Left? *
>
> - A lot of instructions are missing, in particular the vector ones.
> - Legalization of G_SEQUENCE/G_EXTRACT still up in the air for complex
> cases.
>
> Note: The lack of broad vector support is one on the reason we target O0,
> i.e., the vectorizer doesn’t run and we are less likely to hit the missing
> implementation.
>
>
> ** RegBankSelect **
>
> - Core logic is present, no optimizations yet, or more accurately, the
> greedy mode is still pretty silly.
> - TableGen support for RegisterBanks description.
>
> * What’s Left *
>
> - TableGen the instruction mapping from the existing SDISel patterns.
> - Improve the optimization heuristic.
>
>
> ** InstructionSelect **
>
> - Core logic present.
> - TableGen support for simple SDISel patterns (i.e., GISel reuses SDISel
> patterns)
>
> * What’s Left *
>
> - Teach TableGen how to reuse more complex patterns:
> — Patterns with combines in them (e.g., (mull (add)) => madd)
> — Patterns with complex patterns (e.g., SelectAddressModXR0)
>
>
> *** On Going Work ***
>
> - General approach: use AArch64 O0 on the LLVM test suite as a driving
> vehicle to guide what to support next in the various passes.
> - Extend TableGen support to reuse more and more SDISel patterns.
> - ARM port.
> - AMDGPU port.
> - X86 port.
>
> If you have questions, don’t hesitate!
>
> Cheers,
> -Quentin
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170121/59369819/attachment.html>