[LLVMdev] Can I add GlobalVariable in MachineFunctionPass ?

Anthony Yu swpenim at gmail.com
Thu Aug 8 04:29:15 PDT 2013 

Yes, total number of PTX registers that will be emitted is exactly what I
need. It's hard to figure out this in LLVM IR level.


2013/8/7 Justin Holewinski <justin.holewinski at gmail.com>

> Is there any way you could approximate the register/instruction usage and
> perform live-range analysis in a higher-level LLVM IR pass?  I'm not sure
> how useful NVPTXRegisterInfo would be anyway.  Unlike backends that target
> "real" ISAs, these structures do not contain any special properties about
> registers or instructions, like cost or scheduling information.  Are you
> trying to figure out the total number of PTX registers that will be emitted?
>
>
> On Wed, Aug 7, 2013 at 7:06 AM, Anthony Yu <swpenim at gmail.com> wrote:
>
>> OK. I know what you mean.........
>>
>> Simply speaking, I want to do some optimizations for PTX, and the
>> information I need is similar to a register allocator. I know PTX is
>> virtual ISA, but I will use PTX as the input of the simulator, gpgpu-sim,
>> so it makes sense.
>> Whether to insert shared memory is depend on the analysis that needs
>> LiveAnalysis, PTX InstrInfo, PTX RegisterInfo, etc. That's why I need to
>> add global variables in MachineFunctionPass.
>>
>> Antony
>>
>>
>> 2013/8/6 Justin Holewinski <justin.holewinski at gmail.com>
>>
>>> Yes, global variables are the only way to access shared memory.
>>>
>>> I'm just trying to get an idea of what you're aiming to accomplish to
>>> see if we can improve on the interface here.  A MachineFunctionPass runs
>>> after instruction selection and relying on doInitialization to run before
>>> instruction selection is an implementation detail that I do not believe is
>>> guaranteed anywhere (I could be wrong!).  And modifying the IR does in fact
>>> violate the rules for a MachineFunctionPass (see bullet 1 in
>>> http://llvm.org/docs/WritingAnLLVMPass.html#the-machinefunctionpass-class
>>> ).
>>>
>>> If you explain what you're trying to accomplish, I can try to help
>>> figure out a good approach here.  There very well may be limitations to the
>>> current infrastructure that need to be fixed.
>>>
>>>
>>> On Tue, Aug 6, 2013 at 1:25 AM, Anthony Yu <swpenim at gmail.com> wrote:
>>>
>>>> I want to create share memory in my MachineFunctionPass, and insert
>>>> load/store instruction for it. The way to create share memory is to add
>>>> global variables which are in share memory address space (not sure if it is
>>>> the only way). Therefore, I should add global variables in fixed size in
>>>> doInitialization, and record its real size in other place like
>>>> MachineModuleInfo. Then modify or query its real size from that place
>>>> instead of size of variable.
>>>>
>>>>
>>>> Antony
>>>>
>>>>
>>>>
>>>> 2013/8/6 Justin Holewinski <justin.holewinski at gmail.com>
>>>>
>>>>> Can you tell us a bit more about what you're trying to accomplish?
>>>>>
>>>>> Changes to the IR performed during
>>>>> MachineFunctionPass::doInitialization will likely propagate down through
>>>>> code generation, but at that point what is the purpose of using a
>>>>> MachineFunctionPass?  You won't have any analysis or instruction
>>>>> information available until runOnMachineFunction.
>>>>>
>>>>>
>>>>> On Mon, Aug 5, 2013 at 12:00 PM, Anthony Yu <swpenim at gmail.com> wrote:
>>>>>
>>>>>> Micah,
>>>>>>
>>>>>> Thanks for your help. I will study on that code.
>>>>>>
>>>>>>
>>>>>> Justin,
>>>>>>
>>>>>> Sorry for my misleading word. Local memory in OpenCL is the same as
>>>>>> share memory in CUDA. What I mean is share memory, so MachineFrameInfo is
>>>>>> not suitable to me.
>>>>>> And I need codegen data, so FunctionPass is also not suitable.
>>>>>> Anyway, thanks for the suggestion.
>>>>>>
>>>>>> Antony
>>>>>>
>>>>>>
>>>>>>
>>>>>> 2013/8/5 Justin Holewinski <justin.holewinski at gmail.com>
>>>>>>
>>>>>>> If you're running a MachineFunctionPass, then the code has already
>>>>>>> been lowered to machine instructions and modifying the original IR will
>>>>>>> most likely not do what you want.  You should only be using the IR as an
>>>>>>> immutable object for reference.  If you want to change the IR, I would
>>>>>>> suggest using a FunctionPass instead of a MachineFunctionPass.  Unless you
>>>>>>> need codegen data.
>>>>>>>
>>>>>>> At the MachineInstr level, to allocate local memory you can use the
>>>>>>> MachineFrameInfo interface.  This provides methods like CreateStackObject
>>>>>>> to allocate a new stack slot (which will be lowered to local memory in
>>>>>>> PTX).  The return value of these methods is an integer that represents a
>>>>>>> FrameIndex.  You can treat this as a pointer to your allocated object.  You
>>>>>>> will also need to emit the proper MachineInstr-level loads and stores to
>>>>>>> access the object.
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Aug 5, 2013 at 11:00 AM, Anthony Yu <swpenim at gmail.com>wrote:
>>>>>>>
>>>>>>>> Micah,
>>>>>>>>
>>>>>>>> As you expected, I am trying to create local memory but in the
>>>>>>>> NVPTX backend. It's really not convenient that I can't create local memory
>>>>>>>> in runOnMachineFunction.
>>>>>>>> Hmm....
>>>>>>>> Since I should do it at doInitialization stage, I also need to do
>>>>>>>> some tricks in global variable and AsmPrinter to resize it.
>>>>>>>> Did you use the similar way?
>>>>>>>>
>>>>>>>> Antony
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> 2013/8/5 Micah Villmow <micah.villmow at smachines.com>
>>>>>>>>
>>>>>>>>> Antony,
>>>>>>>>>  What are you trying to accomplish in this case? I did something
>>>>>>>>> very similar in the AMDIL backend, but it was not the cleanest solution and
>>>>>>>>> you are correct it has to be do at doInitialization stage and not at
>>>>>>>>> runOnMachineFunction.
>>>>>>>>> Micah
>>>>>>>>>
>>>>>>>>> > -----Original Message-----
>>>>>>>>> > From: llvmdev-bounces at cs.uiuc.edu [mailto:
>>>>>>>>> llvmdev-bounces at cs.uiuc.edu]
>>>>>>>>> > On Behalf Of Antony Yu
>>>>>>>>> > Sent: Monday, August 05, 2013 3:41 AM
>>>>>>>>> > To: llvmdev at cs.uiuc.edu
>>>>>>>>> > Subject: [LLVMdev] Can I add GlobalVariable in
>>>>>>>>> MachineFunctionPass ?
>>>>>>>>> >
>>>>>>>>> > Hello,
>>>>>>>>> >
>>>>>>>>> > I want to add a global variable of arrayType in my
>>>>>>>>> MachineFunctionPass.
>>>>>>>>> > However, I only get const Module from
>>>>>>>>> > MachineFunction.getMMI().getModule().
>>>>>>>>> > I can't add any global variable to a const Module.
>>>>>>>>> > Another way is to add a global variable in doInitialization in my
>>>>>>>>> > MachineFunctionPass, but I can't determine the size of my
>>>>>>>>> arrayType for
>>>>>>>>> > global variable in doInitialization.
>>>>>>>>> >
>>>>>>>>> > Is there any suggestion that can help me achieve this?
>>>>>>>>> >
>>>>>>>>> > Thanks in advance.
>>>>>>>>> > Antony Yu
>>>>>>>>> >
>>>>>>>>> >
>>>>>>>>> >
>>>>>>>>> > --
>>>>>>>>> > View this message in context:
>>>>>>>>> http://llvm.1065342.n5.nabble.com/Can-I-add-
>>>>>>>>> > GlobalVariable-in-MachineFunctionPass-tp60165.html
>>>>>>>>> > Sent from the LLVM - Dev mailing list archive at Nabble.com.
>>>>>>>>> > _______________________________________________
>>>>>>>>> > LLVM Developers mailing list
>>>>>>>>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>>>>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> LLVM Developers mailing list
>>>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Justin Holewinski
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Justin Holewinski
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>>
>>> Thanks,
>>>
>>> Justin Holewinski
>>>
>>
>>
>
>
> --
>
> Thanks,
>
> Justin Holewinski
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130808/c0947314/attachment.html>

More information about the llvm-dev mailing list