llvm dev - Jun 2011 - [LLVMdev] ARM support status (GHC/ARM new calling convention)

Hello Cameron,

thanks a lot for your fast answer, which just makes me curious if making 
ARM tailcalls on par with x86 in the future is on some of the 
development plans already? If not, then what do you think is the 
complexity of such work?

Thanks!
Karel

On 06/17/11 10:41 PM, Cameron Zwarich wrote:
> They work pretty well now, at least on Thumb2 / Darwin. It is still fairly
conservative about when to use tail calls, and doesn't support
GuaranteedTailCallOpt, which might be necessary for GHC.
>
> Cameron
>
> On Jun 17, 2011, at 1:31 PM, Karel Gardas wrote:
>
>>
>> John,
>>
>> I've moved with patches to HEAD and unfortunately the comments
about
>> disabling tailcalls do not go away with this update. Please see
>> ARMTargetLowering::LowerCall in lib/Target/ARM/ARMISelLowering.cpp line
>> 1208 and later. It looks like man can use -arm-tail-calls, but one
never
>> knows how good it is since the comment tells it clearly:
>>
>> // Temporarily disable tail calls so things don't break.
>>
>> so I would like to ask what's the status of tailcalls in LLVM on
ARM
>> platform?
>>
>> Thanks a lot!
>> Karel
>>
>> On 06/16/11 11:00 PM, John McCall wrote:
>>>> Also in the llvm::ARMTargetLowering::LowerCall I see a comment
>>>> about disabling tailcalls just to not break things.
>>>
>>> I believe this has been changed on ToT, so since Haskell is
>>> presumably completely dependent on tail calls working, you'll
need to
>>> work there.
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>

I don't know if GuaranteedTailCallOpt is in anyone's plans. It might be
a good idea to implement some time. I am not sure what GHC's exact needs
are, though.

Cameron

On Jun 17, 2011, at 1:49 PM, Karel Gardas wrote:
> 
> Hello Cameron,
> 
> thanks a lot for your fast answer, which just makes me curious if making
ARM tailcalls on par with x86 in the future is on some of the development plans
already? If not, then what do you think is the complexity of such work?
> 
> Thanks!
> Karel
> 
> On 06/17/11 10:41 PM, Cameron Zwarich wrote:
>> They work pretty well now, at least on Thumb2 / Darwin. It is still
fairly conservative about when to use tail calls, and doesn't support
GuaranteedTailCallOpt, which might be necessary for GHC.
>> 
>> Cameron
>> 
>> On Jun 17, 2011, at 1:31 PM, Karel Gardas wrote:
>> 
>>> 
>>> John,
>>> 
>>> I've moved with patches to HEAD and unfortunately the comments
about
>>> disabling tailcalls do not go away with this update. Please see
>>> ARMTargetLowering::LowerCall in lib/Target/ARM/ARMISelLowering.cpp
line
>>> 1208 and later. It looks like man can use -arm-tail-calls, but one
never
>>> knows how good it is since the comment tells it clearly:
>>> 
>>> // Temporarily disable tail calls so things don't break.
>>> 
>>> so I would like to ask what's the status of tailcalls in LLVM
on ARM
>>> platform?
>>> 
>>> Thanks a lot!
>>> Karel
>>> 
>>> On 06/16/11 11:00 PM, John McCall wrote:
>>>>> Also in the llvm::ARMTargetLowering::LowerCall I see a
comment
>>>>> about disabling tailcalls just to not break things.
>>>> 
>>>> I believe this has been changed on ToT, so since Haskell is
>>>> presumably completely dependent on tail calls working,
you'll need to
>>>> work there.
>>> 
>>> 
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>> 
>> 
>

On 17 June 2011 13:57, Cameron Zwarich <zwarich at apple.com>
wrote:
> I don't know if GuaranteedTailCallOpt is in anyone's plans. It
might be a good idea to implement some time. I am not sure what GHC's exact
needs are, though.
We (GHC) simply rely of the sibling call optimisation:

http://llvm.org/docs/CodeGenerator.html#sibcallopt

We don't use the GuaranteedTailCallOpt any more as we always generate
code that meets the condition for sibling call opt and it generates
much better code than GuaranteedTailCallOpt. (GuaranteedTailCallOpt
did a lot of silly stack ptr movement, not sure if still the case).

Cheers,
David
>
> Cameron
>
> On Jun 17, 2011, at 1:49 PM, Karel Gardas wrote:
>
>>
>> Hello Cameron,
>>
>> thanks a lot for your fast answer, which just makes me curious if
making ARM tailcalls on par with x86 in the future is on some of the development
plans already? If not, then what do you think is the complexity of such work?
>>
>> Thanks!
>> Karel
>>
>> On 06/17/11 10:41 PM, Cameron Zwarich wrote:
>>> They work pretty well now, at least on Thumb2 / Darwin. It is still
fairly conservative about when to use tail calls, and doesn't support
GuaranteedTailCallOpt, which might be necessary for GHC.
>>>
>>> Cameron
>>>
>>> On Jun 17, 2011, at 1:31 PM, Karel Gardas wrote:
>>>
>>>>
>>>> John,
>>>>
>>>> I've moved with patches to HEAD and unfortunately the
comments about
>>>> disabling tailcalls do not go away with this update. Please see
>>>> ARMTargetLowering::LowerCall in
lib/Target/ARM/ARMISelLowering.cpp line
>>>> 1208 and later. It looks like man can use -arm-tail-calls, but
one never
>>>> knows how good it is since the comment tells it clearly:
>>>>
>>>> // Temporarily disable tail calls so things don't break.
>>>>
>>>> so I would like to ask what's the status of tailcalls in
LLVM on ARM
>>>> platform?
>>>>
>>>> Thanks a lot!
>>>> Karel
>>>>
>>>> On 06/16/11 11:00 PM, John McCall wrote:
>>>>>> Also in the llvm::ARMTargetLowering::LowerCall I see a
comment
>>>>>> about disabling tailcalls just to not break things.
>>>>>
>>>>> I believe this has been changed on ToT, so since Haskell is
>>>>> presumably completely dependent on tail calls working,
you'll need to
>>>>> work there.
>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>>
>
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>