[LLVMdev] Using CallingConvLower in ARM target
Sandeep Patel
deeppatel1987 at gmail.com
Fri Feb 13 16:25:27 PST 2009
ARMTargetLowering doesn't need case #1, but it seemed like you and Dan
wanted a more generic way to inject C++ code into the process so I
tried to make the mechanism a bit more general.
deep
On Fri, Feb 13, 2009 at 2:34 PM, Evan Cheng <evan.cheng at apple.com> wrote:
>
> On Feb 13, 2009, at 2:20 PM, Sandeep Patel wrote:
>
>> On Fri, Feb 13, 2009 at 12:33 PM, Evan Cheng <evan.cheng at apple.com>
>> wrote:
>>>
>>> On Feb 12, 2009, at 6:21 PM, Sandeep Patel wrote:
>>>
>>>> Although it's not generally needed for ARM's use of CCCustom, I
>>>> return
>>>> two bools to handle the four possible outcomes to keep the mechanism
>>>> flexible:
>>>>
>>>> * if CCCustomFn handled the arg or not
>>>> * if CCCustomFn wants to end processing of the arg or not
>>>
>>> +/// CCCustomFn - This function assigns a location for Val, possibly
>>> updating
>>> +/// all args to reflect changes and indicates if it handled it. It
>>> must set
>>> +/// isCustom if it handles the arg and returns true.
>>> +typedef bool CCCustomFn(unsigned &ValNo, MVT &ValVT,
>>> + MVT &LocVT, CCValAssign::LocInfo &LocInfo,
>>> + ISD::ArgFlagsTy &ArgFlags, CCState &State,
>>> + bool &result);
>>>
>>> Is "result" what you refer to as "isCustom" in the comments?
>>>
>>> Sorry, I am still confused. You mean it could return true but set
>>> 'result' to false? That means it has handled the argument but it
>>> would
>>> not process any more arguments? What scenario do you envision that
>>> this will be useful? I'd rather keep it simple.
>>
>> As you note there are three actual legitimate cases (of the four
>> combos):
>>
>> 1. The CCCustomFn wants the arg handling to proceed. This might be
>> used akin to CCPromoteToType.
>> 2. The CCCustomFn entirely handled the arg. This might be used akin to
>> CCAssignToReg.
>> 3. The CCCustomFn tried to handle the arg, but failed.
>>
>> these results are conveyed the following ways:
>>
>> 1. The CCCustomFn returns false, &result is not used.
>> 2. The CCCustomFn returns true, &result is false;
>> 3. The CCCustomFn returns true, &result is true.
>
> I don't think we want to support #1. If the target want to add custom
> code to handle an argument, if should be responsible for outputting
> legal code. Is there an actual need to support #1?
>
> Evan
>
>>
>>
>> I tried to keep these CCCustomFns looking like TableGen generated
>> code. Suggestions of how to reorganize these results are welcome. :-)
>> Perhaps better comments around the typedef for CCCustomFn would
>> suffice?
>>
>> The isCustom flag is simply a means for this machinery to convey to
>> the TargetLowering functions to process this arg specially. It may not
>> always be possible for the TargetLowering functions to determine that
>> the arg needs special handling after all the changes made by the
>> CCCustomFn or CCPromoteToType and other transformations.
>>
>>>> I placed the "unsigned i" outside those loops because i is used
>>>> after
>>>> the loop. If there's a better index search pattern, I'd be happy to
>>>> change it.
>>>
>>> Ok.
>>>
>>> One more nitpick:
>>>
>>> +/// CCCustom - calls a custom arg handling function
>>>
>>> Please capitalize "calls" and end with a period.
>>
>> Once we settle on the result handling changes, I'll submit an update
>> with this change.
>>
>>> Thanks,
>>>
>>> Evan
>>>
>>>>
>>>>
>>>> Attached is an updated patch against HEAD that has DebugLoc
>>>> changes. I
>>>> also split out the ARMAsmPrinter fix into it's own patch.
>>>>
>>>> deep
>>>>
>>>> On Mon, Feb 9, 2009 at 8:54 AM, Evan Cheng <echeng at apple.com> wrote:
>>>>> Thanks Sandeep. I did a quick scan, this looks really good. But I
>>>>> do
>>>>> have a question:
>>>>>
>>>>> +/// CCCustomFn - This function assigns a location for Val,
>>>>> possibly
>>>>> updating
>>>>> +/// all args to reflect changes and indicates if it handled it. It
>>>>> must set
>>>>> +/// isCustom if it handles the arg and returns true.
>>>>> +typedef bool CCCustomFn(unsigned &ValNo, MVT &ValVT,
>>>>> + MVT &LocVT, CCValAssign::LocInfo &LocInfo,
>>>>> + ISD::ArgFlagsTy &ArgFlags, CCState &State,
>>>>> + bool &result);
>>>>>
>>>>> Is it necessary to return two bools (the second is returned by
>>>>> reference in 'result')? I am confused about the semantics of
>>>>> 'result'.
>>>>>
>>>>> Also, a nitpick:
>>>>>
>>>>> + unsigned i;
>>>>> + for (i = 0; i < 4; ++i)
>>>>>
>>>>> The convention we use is:
>>>>>
>>>>> + for (unsigned i = 0; i < 4; ++i)
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Evan
>>>>>
>>>>> On Feb 6, 2009, at 6:02 PM, Sandeep Patel wrote:
>>>>>
>>>>>> I think I've got all the cases handled now, implementing with
>>>>>> CCCustom<"foo"> callbacks into C++.
>>>>>>
>>>>>> This also fixes a crash when returning i128. I've also included a
>>>>>> small asm constraint fix that was needed to build newlib.
>>>>>>
>>>>>> deep
>>>>>>
>>>>>> On Mon, Jan 19, 2009 at 10:18 AM, Evan Cheng
>>>>>> <evan.cheng at apple.com>
>>>>>> wrote:
>>>>>>>
>>>>>>> On Jan 16, 2009, at 5:26 PM, Sandeep Patel wrote:
>>>>>>>
>>>>>>>> On Sat, Jan 3, 2009 at 11:46 AM, Dan Gohman <gohman at apple.com>
>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>> One problem with this approach is that since i64 isn't legal,
>>>>>>>>> the
>>>>>>>>> bitcast would require custom C++ code in the ARM target to
>>>>>>>>> handle properly. It might make sense to introduce something
>>>>>>>>> like
>>>>>>>>>
>>>>>>>>> CCIfType<[f64], CCCustom>
>>>>>>>>>
>>>>>>>>> where CCCustom is a new entity that tells the calling
>>>>>>>>> convention
>>>>>>>>> code to to let the target do something not easily representable
>>>>>>>>> in the tablegen minilanguage.
>>>>>>>>
>>>>>>>> I am thinking that this requires two changes: add a flag to
>>>>>>>> CCValAssign (take a bit from HTP) to indicate isCustom and a way
>>>>>>>> to
>>>>>>>> author an arbitrary CCAction by including the source directly in
>>>>>>>> the
>>>>>>>> TableGen mini-language. This latter change might want a generic
>>>>>>>> change
>>>>>>>> to the TableGen language. For example, the syntax might be like:
>>>>>>>>
>>>>>>>> class foo : CCCustomAction {
>>>>>>>> code <<< EOF
>>>>>>>> ....multi-line C++ code goes here that allocates regs & mem
>>>>>>>> and
>>>>>>>> sets CCValAssign::isCustom....
>>>>>>>> EOF
>>>>>>>> }
>>>>>>>>
>>>>>>>> Does this seem reasonable? An alternative is for CCCustom to
>>>>>>>> take a
>>>>>>>> string that names a function to be called:
>>>>>>>>
>>>>>>>> CCIfType<[f64], CCCustom<"MyCustomLoweringFunc">>
>>>>>>>>
>>>>>>>> the function signature for such functions will have to return
>>>>>>>> two
>>>>>>>> results: if the CC processing is finished and if it the func
>>>>>>>> succeeded
>>>>>>>> or failed:
>>>>>>>
>>>>>>> I like the second solution better. It seems rather cumbersome to
>>>>>>> embed
>>>>>>> multi-line c++ code in td files.
>>>>>>>
>>>>>>> Evan
>>>>>>>>
>>>>>>>>
>>>>>>>> typedef bool CCCustomFn(unsigned ValNo, MVT ValVT,
>>>>>>>> MVT LocVT, CCValAssign::LocInfo LocInfo,
>>>>>>>> ISD::ArgFlagsTy ArgFlags, CCState &State,
>>>>>>>> bool &result);
>>>>>>>> _______________________________________________
>>>>>>>> LLVM Developers mailing list
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>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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>>>>>>>
>>>>>> <
>>>>>> arm_callingconv
>>>>>> .diff>_______________________________________________
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>>>> <
>>>> arm_callingconv
>>>> .diff
>>>> ><arm_fixes.diff>_______________________________________________
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