[llvm-commits] The AArch64 LLVM (& Clang) target

[Jim Grosbach]

Hi Tim,

I'm excited to see this making its way into the public tree. Thanks for seeing it through!

Now that I'm back from vacation, I'll hopefully have some time to look things over and give more substantive feedback in addition to the cheerleading. :)

Until then, a few quick questions:

NEON: Are the instructions themselves there, but no intrinsics support, or are the instruction definitions missing as well?
PIC: Is there a non-PIC mode? I would have expected (naively?) that this arch would be such that there'd be negligible benefit to a non-PIC model.
MCJIT: Why not? Given direct-to-object-file integrated assembler support (which it sounds like you have), enabling this should be pretty trivial.
Memory model: Why 4GB and not the full 64-bit address space?
Testing: I assume this is done via a simulator/emulator? What's the status of the LLVM test-suite running on it? Everything passing?

Regards,

-Jim


On Jan 7, 2013, at 4:57 AM, Tim Northover <tim.northover at arm.com> wrote:

> Hi all,
> 
> I now finally have permission to start upstreaming the long-delayed backend
> for
> ARM's new 64-bit architecture, AArch64.
> 
> In summary, we're proposing this backend for inclusion into LLVM; first as an
> experimental target, but with a view to being fully supported as soon as
> possible.
> 
> Splitting up an entire target into smaller patches is rather tricky, but I've
> isolated all changes to generic LLVM code. I'll be sending those patches out
> for individual review and wouldn't consider committing until all that's left
> in the backend patch is very definitely AArch64 specific. Let me know if
> there's anything else I can do to help.
> 
> Meanwhile, the patch attached here *does* contain those generic changes, which
> should probably be ignored for review purposes. They're present so that
> someone curious can simply apply a single patch and get a working backend.
> 
> The current status of the backend is roughly as follows:
>  + In a large scale: C99 and C++03 code targeting ELF on Linux should be
>    supported. Problems there will be a high priority and are probably unknown
>    to us.
>  + Initial support for using NEON instructions is underway, being implemented
>    by Ana Pazos from Qualcomm (thanks!). This is not complete though and
>    should not be expected to work for generic code yet.
>  + The backend produces mostly unoptimised code. Work has been mainly on
>    features, with the lack of hardware making more detailed performance
>    analysis less useful at present.
>  + DWARF debugging should be supported.
>  + Position-independent code should be supported.
>  + Thread-local storage (GNU, rather than C++11) should be supported.
>  + Inline assembly should be supported.
>  + There is no MCJIT (or any other JIT) support.
>  + Only one memory model is supported: code and statically allocated data
>    must occupy a contiguous 4GB space (a.k.a. "large").
> 
> There are some areas known to need refactoring, but where we refrained to
> avoid large merge conflicts. I would prefer the nastiest of these to be
> delayed and form part of the Experimental -> Stable target transition, where
> merges will hopefully be less painful. Most notably the ConstantIslandPass
> should probably be shared between AArch32 and AArch64.
> 
> If there's anything we can do to make this process easier for people, please
> let me know (a branch in svn? Upload patch to phabricator? ...). Similarly,
> any other questions or comments would be welcome.
> 
> Cheers.
> 
> Tim.
> 
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