llvm dev - Jan 2017 - Tail calls and portability

I have been working on adding proper tail (via `become`) to rustc.  I was
able to make them work (some parts of the type checker aren't implemented
yet).  However, I ran into an LLVM-related problem.

LLVM claims to support proper tail calls when fastcc is used — but only on
i386, x86-64 and PowerPC.  Is this accurate? Will proper tail calls be
supported on WebAssembly?  Are they supported on ARM? AArch64? Other
backends?
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As a general “good practice", you should answer to your own thread you
started this morning instead of starting a new one with little difference:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/108678.html

+CC WebAssembly folks to make sure they don’t miss this question.

— 
Mehdi


> On Jan 4, 2017, at 7:07 PM, Demi Obenour via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> I have been working on adding proper tail (via `become`) to rustc.  I was
able to make them work (some parts of the type checker aren't implemented
yet).  However, I ran into an LLVM-related problem.
> 
> LLVM claims to support proper tail calls when fastcc is used — but only on
i386, x86-64 and PowerPC.  Is this accurate? Will proper tail calls be supported
on WebAssembly?  Are they supported on ARM? AArch64? Other backends?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

The current version of the WebAssembly ISA doesn't support tail calls. It
is likely that support will be added in future versions.

Dan


On Jan 4, 2017 8:34 PM, "Mehdi Amini" <mehdi.amini at apple.com>
wrote:

As a general “good practice", you should answer to your own thread you
started this morning instead of starting a new one with little difference:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/108678.html

+CC WebAssembly folks to make sure they don’t miss this question.

—
Mehdi


> On Jan 4, 2017, at 7:07 PM, Demi Obenour via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
> I have been working on adding proper tail (via `become`) to rustc.  I was
able to make them work (some parts of the type checker aren't implemented
yet).  However, I ran into an LLVM-related problem.
>
> LLVM claims to support proper tail calls when fastcc is used — but only
on i386, x86-64 and PowerPC.  Is this accurate? Will proper tail calls be
supported on WebAssembly?  Are they supported on ARM? AArch64? Other
backends?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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On Wed, Jan 04, 2017 at 10:07:34PM -0500, Demi Obenour via llvm-dev
wrote:
> LLVM claims to support proper tail calls when fastcc is used — but only on
> i386, x86-64 and PowerPC.  Is this accurate? Will proper tail calls be
> supported on WebAssembly?  Are they supported on ARM? AArch64? Other
> backends?
Note that tail calls on PowerPC can run into the TOC-restoration issue
for non-PIC calls.

Joerg

There is some support for tail calls for MIPS, but it is not enabled by default
yet.

Thanks,
Simon

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Demi
Obenour via llvm-dev
Sent: 05 January 2017 03:08
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] Tail calls and portability

I have been working on adding proper tail (via `become`) to rustc.  I was able
to make them work (some parts of the type checker aren't implemented yet). 
However, I ran into an LLVM-related problem.

LLVM claims to support proper tail calls when fastcc is used — but only on i386,
x86-64 and PowerPC.  Is this accurate? Will proper tail calls be supported on
WebAssembly?  Are they supported on ARM? AArch64? Other backends?

On 1/4/2017 9:07 PM, Demi Obenour via llvm-dev wrote:
> I have been working on adding proper tail (via `become`) to rustc.  I
> was able to make them work (some parts of the type checker aren't
> implemented yet).  However, I ran into an LLVM-related problem.
>
> LLVM claims to support proper tail calls when fastcc is used — but only
> on i386, x86-64 and PowerPC.  Is this accurate? Will proper tail calls
> be supported on WebAssembly?  Are they supported on ARM? AArch64? Other
> backends?
Hexagon uses tail calls in the right circumstances, but it ignores musttail.

-Krzysztof

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