[PATCH] Add two new calling conventions for runtime calls

[Juergen Ributzka]

Committed in r199508.

On Jan 16, 2014, at 2:42 PM, Philip Reames <listmail at philipreames.com> wrote:

> Your revised naming scheme would be fine by me.  
> 
> We actually have several different calling conventions in use.  Our compiled-code-to-assembly-stub conventions is quite close to your proposed CPreservesMost, except that we occasionally use a dual-register return variant for some calls.  Our compiled-to-compiled convention is a slightly rotated form of the C calling convention.  When we make calls from compiled code into C code (via a hand written assembly stub), we want to be able to easily insert a leading argument without having to shift all other arguments. (i.e. for JNI)
> 
> Things to consider for your documentation:
> - Is this defined to match the objc runtime?  If so, which?  Or is defined in terms of a variant of the C calling convention which ObjC happens to use?  Or is it defined in terms of purpose and only valid against code compiled by the same version of LLVM with the same convention name?  (i.e. compatibility guarantees)
> - What is the difference between these and existing calling conventions?  In particular, "cold"?  When should each be used?
> - How should target neutral front ends use the conventions?  
> 
> You don't need to answer any of those directly to me.  Just provide some documentation which addresses them to some degree.  (The most important is the first.)
> 
> Philip
> 
> On 1/16/14 11:23 AM, Juergen Ributzka wrote:
>> Hi Philip,
>> 
>> thanks for looking at this. I am definitely open for better names for the calling conventions. Although I would prefer not to use GPR or XMM in them, because they are not only meant for X86. Also on a different architecture with different standard calling conventions a different mix of registers might make more sense. ObjC is currently the initial use for this, but we don’t want to limit it to just this one particular runtime. The more people can use this the better.
>> 
>> What about CPreservesMost and CPreservesAll?
>> 
>> How different is your special calling convention?
>> 
>> Thanks
>> 
>> Cheers,
>> Juergen
>> 
>>  
>> On Jan 16, 2014, at 10:45 AM, Philip Reames <listmail at philipreames.com> wrote:
>> 
>>> On 1/16/14 10:39 AM, Philip Reames wrote:
>>>> My only objection to this patch is the naming.  We also have runtime calls with special calling conventions, but ours aren't the same as the ones specified here. Could we rename these?
>>>> 
>>>> A few random ideas for names:
>>>> CPreserveGPR
>>>> CPreserveGPRXMM
>>>> WebKitRuntimeCC
>>> Correction: ObjCRuntime.  It helps if I read the original email more closely.
>>>> 
>>>> Also, should these be prefixed with X86_?
>>>> 
>>>> Philip
>>>> 
>>>> On 1/15/14 10:41 AM, Lang Hames wrote:
>>>>> Hi Juergen,
>>>>> 
>>>>> If these calling conventions are intended to be generic, should a
>>>>> description be added to the LangRef?
>>>>> 
>>>>> Otherwise LGTM.
>>>>> 
>>>>> - Lang.
>>>>> 
>>>>> On Tue, Jan 14, 2014 at 3:11 PM, Juergen Ributzka <juergen at apple.com> wrote:
>>>>>> ping
>>>>>> 
>>>>>> On Jan 10, 2014, at 7:45 PM, Juergen Ributzka <juergen at apple.com> wrote:
>>>>>> 
>>>>>>> New rebased patch and a small fix to the label check in the unit test.
>>>>>>> 
>>>>>>> Cheers,
>>>>>>> Juergen
>>>>>>> 
>>>>>>> <0002-Add-two-new-calling-conventions-for-runtime-calls.patch>
>>>>>>> On Jan 10, 2014, at 3:47 PM, Juergen Ributzka <juergen at apple.com> wrote:
>>>>>>> 
>>>>>>>> Hi @ll,
>>>>>>>> 
>>>>>>>> this patch adds two new target-independent calling conventions for runtime calls - Runtime and FastRuntime.
>>>>>>>> 
>>>>>>>> The target-specific implementation for X86-64 is defined as following:
>>>>>>>>      - Arguments are passed as for the default C calling convention
>>>>>>>>      - The same applies for the return value(s)
>>>>>>>>      - for runtimecc the callee preserves all GPRs - except R11
>>>>>>>>      - for fastruntimecc the callee preserves all GPRs and all XMMs - except R11
>>>>>>>> 
>>>>>>>> The idea is to provide calling conventions for calls to very hot runtime functions that are normally just a few lines of assembly code and don’t require a lot of registers. This could be used by the ObjectiveC runtime, or any other runtime that provides performance critical functions.
>>>>>>>> 
>>>>>>>> The FastRuntime CC is intended to be used for small codes that don’t call any other functions at all.
>>>>>>>> The Runtime CC is also intended for small codes that usually don’t call other functions on the fast path, but might have to on the slow path.
>>>>>>>> 
>>>>>>>> Cheers,
>>>>>>>> Juergen
>>>>>>>> 
>>>>>>>> <0001-Add-two-new-calling-conventions-for-runtime-calls.patch>
>>>>>>>> 
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> 

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