[llvm-dev] Do I need to implement CCAssignFnForCall for porting GlobalISel to AVR target?

[Leslie Zhai via llvm-dev]

Hi Diana,

Thanks for your kind response!

Yes, ARM target is more complex than AVR to getEffectiveCallingConv ID 
https://github.com/llvm-mirror/llvm/blob/master/lib/Target/ARM/ARMISelLowering.cpp#L1559 
    I need to read ARM's code carefully.


在 2017年11月29日 18:23, Diana Picus 写道:
> Hi Leslie,
>
> Long story short - no, you don't need CCAssignFnForCall.
>
> In fact, if you look at the X86CallLowering, you'll see that it
> doesn't use that either, since it can use CC_X86 directly. For ARM it
> made sense to have a CCAssignFnForCall so we could reuse the code in
> ARMISelLowering.
>
> I don't know the AVR backend very well, so I can't help you figure out
> what is most appropriate for the AVR target. Having a CCAssignFn
> available would make it easier to use the existing infrastructure, but
> in principle you should be able to get away without one if you
> override ValueHandler::assignArg. After a cursory look at
> AVRISelLowering, I see it has some custom code for analyzing arguments
> - you'll probably have to somehow incorporate that logic into
> assignArg.
>
> Hope that helps,
> Diana
>
> On 29 November 2017 at 05:00, Leslie Zhai <lesliezhai at llvm.org.cn> wrote:
>> Hi LLVM developers,
>>
>> I am porting GlobalISel to AVR target by learning ARM target's source code
>>
>>
>> commit c82e7ec9e25c934568eb9c75cf13226177e98dba
>> Author: Diana Picus <diana.picus at linaro.org>
>> Date:   Fri Dec 16 10:35:20 2016 +0000
>>
>>      [ARM] Expose methods to get the CCAssignFn. NFCI
>>
>>      Add two public methods to ARMTargetLowering: CCAssignFnForCall and
>>      CCAssignFnForReturn, which are just calling the already existing private
>> method
>>      CCAssignFnForNode. These will come in handy for GlobalISel on ARM.
>>
>>      We also replace all calls to CCAssignFnForNode in ARMISelLowering.cpp,
>> because
>>      the new methods are friendlier to the reader.
>>
>>
>> There are:
>>
>> CCAssignFnForCall
>>
>> and
>>
>> CCAssignFnForReturn
>>
>> But there is only CCAssignFnForReturn for AVR, do I need to implement
>> CCAssignFnForCall for AVR target?
>>
>>
>> diff --git a/lib/Target/AVR/AVRCallingConv.td
>> b/lib/Target/AVR/AVRCallingConv.td
>> index 68dbce0..d460925 100644
>> --- a/lib/Target/AVR/AVRCallingConv.td
>> +++ b/lib/Target/AVR/AVRCallingConv.td
>> @@ -10,6 +10,18 @@
>>
>> //===----------------------------------------------------------------------===//
>>
>>
>> //===----------------------------------------------------------------------===//
>> +// AVR Calling Convention
>> +//===----------------------------------------------------------------------===//
>> +
>> +def CC_AVR : CallingConv
>> +<[
>> +]>;
>> +
>> +def CC_AVR_BUILTIN : CallingConv
>> +<[
>> +]>;
>> +
>> +//===----------------------------------------------------------------------===//
>>   // AVR Return Value Calling Convention
>>
>> //===----------------------------------------------------------------------===//
>>
>> diff --git a/lib/Target/AVR/AVRISelLowering.cpp
>> b/lib/Target/AVR/AVRISelLowering.cpp
>> index a49da15..44f0ed6 100644
>> --- a/lib/Target/AVR/AVRISelLowering.cpp
>> +++ b/lib/Target/AVR/AVRISelLowering.cpp
>> @@ -1324,12 +1324,13 @@ SDValue AVRTargetLowering::LowerCallResult(
>>   //               Return Value Calling Convention Implementation
>>
>> //===----------------------------------------------------------------------===//
>>
>> -CCAssignFn *AVRTargetLowering::CCAssignFnForReturn(CallingConv::ID CC)
>> const {
>> +CCAssignFn *AVRTargetLowering::CCAssignFnForReturn(CallingConv::ID CC,
>> +                                                   bool Return) const {
>>     switch (CC) {
>>     case CallingConv::AVR_BUILTIN:
>> -    return RetCC_AVR_BUILTIN;
>> +    return Return ? RetCC_AVR_BUILTIN : CC_AVR_BUILTIN;
>>     default:
>> -    return RetCC_AVR;
>> +    return Return ? RetCC_AVR : CC_AVR;
>>     }
>>   }
>>
>> diff --git a/lib/Target/AVR/AVRISelLowering.h
>> b/lib/Target/AVR/AVRISelLowering.h
>> index c90c65c..43777a2 100644
>> --- a/lib/Target/AVR/AVRISelLowering.h
>> +++ b/lib/Target/AVR/AVRISelLowering.h
>> @@ -127,6 +127,8 @@ public:
>>     unsigned getRegisterByName(const char* RegName, EVT VT,
>>                                SelectionDAG &DAG) const override;
>>
>> +  CCAssignFn *CCAssignFnForReturn(CallingConv::ID CC, bool Return = true)
>> const;
>> +
>>   private:
>>     SDValue getAVRCmp(SDValue LHS, SDValue RHS, ISD::CondCode CC, SDValue
>> &AVRcc,
>>                       SelectionDAG &DAG, SDLoc dl) const;
>> @@ -140,8 +142,6 @@ private:
>>     SDValue LowerSETCC(SDValue Op, SelectionDAG &DAG) const;
>>     SDValue LowerVASTART(SDValue Op, SelectionDAG &DAG) const;
>>
>> -  CCAssignFn *CCAssignFnForReturn(CallingConv::ID CC) const;
>> -
>>     bool CanLowerReturn(CallingConv::ID CallConv,
>>                         MachineFunction &MF, bool isVarArg,
>>                         const SmallVectorImpl<ISD::OutputArg> &Outs,
>>
>>
>> Please give me some hint, thanks a lot!
>>
>> --
>> Regards,
>> Leslie Zhai - https://reviews.llvm.org/p/xiangzhai/
>>
>>
>>

-- 
Regards,
Leslie Zhai - https://reviews.llvm.org/p/xiangzhai/