[LLVMdev] Can I add GlobalVariable in MachineFunctionPass ?

Wed Aug 7 04:06:07 PDT 2013

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
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>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Justin Holewinski
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>>
>>> Thanks,
>>>
>>> Justin Holewinski
>>>
>>
>>
>
>
> --
>
> Thanks,
>
> Justin Holewinski
>
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