[LLVMdev] AArch64: GHC compilation issue.

Karel Gardas karel.gardas at centrum.cz
Thu Jan 9 13:39:14 PST 2014


small misunderstanding. I'm not dealing with unregisterised via C build, 
but with unregisterised with LLVM, which is a little bit different beast.


On 01/ 9/14 10:23 PM, Carter Schonwald wrote:
> Hey Karel,
> the GHC unregisterized via C code gen requires using GCC. Unless Clang
> starts support some of the more eclectic GCC C extensions, you wont' be
> able to use Clang/LLVM for doing an unregisterized build.
> GCC 4.8 and newer seems to have aarch64 support.
> cheers!
> -Carter
> On Wed, Jan 8, 2014 at 4:51 PM, Karel Gardas <karel.gardas at centrum.cz
> <mailto:karel.gardas at centrum.cz>> wrote:
>     Hi Tim,
>     On 01/ 8/14 10:24 PM, Tim Northover wrote:
>         Hi Karel,
>             I've observed the same issue with LLVM 3.4 as distributed by
>             Ubuntu 13.10
>             and with LLVM HEAD compiled on January 6. I'm able to
>             provide the byte-code
>             file which results in this issue, but would first like to
>             know if this is a
>             known issue in AArch64 target support or if I shall submit
>             it somewhere or
>             even if I did some mistake in invoking llc or providing
>             wrong set of options
>             to it.
>         I've certainly not seen similar. Usually "Cannot select" errors are
>         fixed very quickly since they're so easy to narrow down and fix. I
>         think this is a real bug and the .ll file would be very useful.
>     the bziped2 file is here for you
>     https://app.box.com/s/__0i43c5j1bq40yheocmn9
>     <https://app.box.com/s/0i43c5j1bq40yheocmn9>
>             It compiles to amd64 code by default so I added just
>             -march=aarch64
>             and was in impression that it should be enough to target
>             AArch64 platform...
>             If that's wrong, please let me know.
>         That's on the edge of OK. There are numerous tricky ABI issues that
>         could be caused by simply swapping a -march argument to LLVM .
>         Clang,
>         for example, wouldn't be able to compile correct C or C++ code with
>         just that switch. But GHC presumably has less stringent ABI
>         compatibility requirements, so it might get away with it.
>     I hope so.
>         On the other hand, I think x86 (and possibly ARM) has specific
>         code to
>         handle the GHC calling conventions, which I'm fairly sure AArch64
>         doesn't. That *might* just be a matter of performance, or it
>         might be
>         crucial. I kept meaning to get GHC working but never really got
>         around
>         to it.
>     Ah, I've not mentioned it before, but I'm attempting to port GHC to
>     AArch64 and the first step is to get so called unregisterised build
>     working. Unregisterised build does not require this specific GHC calling
>     convention. Once this is working I'll come here hopefully with some
>     patch or with ask for idea/help with modification of AArch64 target
>     support to make GHC calling convention a reality. But certainly I'm not
>     there yet...
>     Hmm, but since you mentioned it. Has anything changed in the LLVM so
>     it's more easy to write such calling convention? IIRC, the calling
>     convention is here just to tell LLVM to omit usage of some registers as
>     they are pinned to the haskell virtual registers... I hope I'm not too
>     misleading here...And in the past creating such calling convention where
>     the required regs were removed was the only way probably...
>     Thanks!
>     Karel
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