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digitalmars.D - macOS Big Sur status report

reply Guillaume Piolat <first.last gmail.com> writes:
Hello,

I'd like to post here to get you in touch with the future support 
of macOS Big Sur.



---------------------------

1. Context


Future Mac comes with "Apple Silicon" CPU that are natively arm64.

On these system (out end of 2020), you can run both x86_64 and 
arm64 executables.

As of today, a D program works unchanged under macOS Big Sur 
(11.0). It is emulated. The new processors are really fast and 
it's surprisingly painless.

So there is no real urgency for transitioning, apart from keeping 
native performance. For maximum compatibility one would 
distribute "fat binaries", a arm64 executable stitched to a 
x86_64 executable with the "lipo" tool.


-------------------

2. druntime support

The triple is: arm64-apple-macos and currently it needs tweaks to

A druntime built for macOS 11.0 doesn't exist yet but is in the 
works.
druntime needs to be a bit adapted for Big Sur. It's mostly C 
symbols that used to have OSX-specific names; it requires 
extra-care.

You can thankfully hack around the current lack of runtime with 
LDC by linking with the druntime built for iOS.

See progress here: 
https://github.com/ldc-developers/ldc/issues/3559

I'm just unaware which druntime needs to be touched: the LDC one 
or upstream?


--------------

3. DUB support

It appears nothing needs to be done since DUB supports triple in 
the -a flag.

$ dub -a arm64-apple-macos


---------------------------

4. intel-intrinsics support

The idea is to keep the x86 semantics of intel-intrinsics and get 
it to work on arm64, at a slight performance loss. The extent of 
the impedence mismatch is unknown yet.

This is a similar idea to the "simde" library on Github.

For now the goal has been to get to the same semantics through 
the generic intrinsic implementations, and to get back 
performance later.

For now the goal was to find a way to respect the rounding 
semantics.

ARM have no MXCSR, rounding mode and flush-to-zero mode are put 
into the ARM's FPCSR control word instead.

As there is no new ARM instruction to round using the current 
rounding mode (which is definately a good design), we dispatch 
after reading that control word.

What is unsupported for now is:
- FP exceptions flags and FP exceptions masks
- most intrinsics should be really slow. It will need detailed 
work to ensure the fastest implementation of each and every x86 
intrinsic.


Thanks for reading and consider donating to LDC!
Sep 13 2020
next sibling parent reply Jacob Carlborg <doob me.com> writes:
On Sunday, 13 September 2020 at 19:51:14 UTC, Guillaume Piolat 
wrote:

 Hello,

 I'd like to post here to get you in touch with the future 
 support of macOS Big Sur.


Thanks for looking into this.


 1. Context


 Future Mac comes with "Apple Silicon" CPU that are natively 
 arm64.

 On these system (out end of 2020), you can run both x86_64 and 
 arm64 executables.

 As of today, a D program works unchanged under macOS Big Sur 
 (11.0). It is emulated. The new processors are really fast and 
 it's surprisingly painless.


I would like to add, for clarity, that macOS Big Sur runs 
natively on existing Macs which runs x86-64. D works without any 
problems, out of the box on these systems. This post is 
specifically about the new Apple Silicon, ARM64 (AArch64).


 I'm just unaware which druntime needs to be touched: the LDC 
 one or upstream?


As much as possible upstream. Hopefully it shouldn't be that much 
since it works on iOS. There might be some required changes to 
Phobos as well.

--
/Jacob Carlborg
Sep 15 2020
next sibling parent Steven Schveighoffer <schveiguy gmail.com> writes:
On 9/15/20 6:08 AM, Jacob Carlborg wrote:

 On Sunday, 13 September 2020 at 19:51:14 UTC, Guillaume Piolat wrote:

 I'm just unaware which druntime needs to be touched: the LDC one or 
 upstream?


 
 As much as possible upstream. Hopefully it shouldn't be that much since 
 it works on iOS. There might be some required changes to Phobos as well.


I suspect DMD will not ever build binaries for the ARM architecture. But 
I second Jacob's view, we do not want diverging versions of druntime if 
we can help it. I know LDC already has slightly different code, but we 
should try to minimize that, and keep them in sync as much as possible 
using version statements.

-Steve
Sep 15 2020
prev sibling parent Guillaume Piolat <first.last gmail.com> writes:
On Tuesday, 15 September 2020 at 10:08:05 UTC, Jacob Carlborg 
wrote:

 Thanks for looking into this.


My pleasure.



 As much as possible upstream. Hopefully it shouldn't be that 
 much since it works on iOS. There might be some required 
 changes to Phobos as well.


Indeed, the real work was done for iOS. I'm just piggy-backing.

Update:

`intel-intrinsics` now passes unittests on AArch64. There are 
about 20 intrinsics that will need further optimization, for 
example _mm_cvtps_epi32() or _mm_avg_epi16(). Thanks to LLVM a 
lot of intrinsics written for x86 are already optimal on ARM.
Sep 15 2020
prev sibling parent Guillaume Piolat <first.name guess.com> writes:
On Sunday, 13 September 2020 at 19:51:14 UTC, Guillaume Piolat 
wrote:

 I'd like to post here to get you in touch with the future 
 support of macOS Big Sur.


Update on Big Sur support:

- LDC 1.024 has been released with experimental support for 
targeting macOS on 64-bit ARM 
(https://forum.dlang.org/post/gsmunhwpulpwjphnuoed forum.dlang.org).
   On Big Sur, a lot of things work such as building programs with 
`-mtriple=arm64-apple-macos`, building Universal Binaries with 
lipo, Obj-C bindings...
    Future work include identifying the remaining ABI problems.

- `intel-intrinsics` when used with LDC will produce optimized 
code for arm64 (Big Sur), and working but slow code for ARM32 
(Raspberry Pi). The Pi being a side-product from supporting 
ARM64. Updated table in: 
https://github.com/AuburnSounds/intel-intrinsics
    There IS some impedance mismatch between SSE and Neon at 
times. ARM is really quite a different beast.
Oct 25 2020