[LLVMdev] Interprocedural Register Allocation

[Madhusudan C.S]

Hi,
   Can some one please help me with this problem? From what I understand:

const PassInfo *PassRegistry::getPassInfo(const void *TI) const in
lib/VMCore/PassRegistry.cpp

method returns 0 when it is expected to return a pass info. I am not sure
what PassInfo is expected here. I tried to put a few DEBUG statements
within that method but I could not find the information needed. So some
pass is not being registered.

Can some one please help me?


On Fri, Dec 7, 2012 at 7:23 AM, Madhusudan C.S <madhusudancs at gmail.com>wrote:

> Hi Jakob,
>
> I have been trying to learn how the CodeGen passes work and I am playing
> around with the -debug-pass option. I tried implementing a bare
> CallGraphSCCPass based Pass in the CodeGen which basically does nothing for
> now. I mostly tried to replicate what RegAlloc passes do. I did this
> instead of modifying the existing RegAlloc passes to use CallGraphSCCPass
> because that was becoming way too complicated for simple experiments I was
> trying when I tried to do that. I am attaching the diffs of what I actually
> tried to do for reference here. It is not really well documented and there
> is a lot of copy/paste code there, but well, this is not really the final
> code to be submitted or anything, just to play around, so I have not really
> put efforts into comments etc. yet.
>
>
> So when I build LLVM and try to run the pass with the following command:
> $ llc --debug -cgregalloc=cg <$HOME/cpptry/manyfuncs.bc
>
> I get the following error.
>
> Args: llc --debug -cgregalloc=cg
> Subtarget features: SSELevel 6, 3DNowLevel 0, 64bit 1
> Pass ID not registered
> UNREACHABLE executed at /media/python/workspace/llvm/
> lib/CodeGen/Passes.cpp:324!
> 0  llc             0x0000000001453dfe
> 1  llc             0x00000000014542fa
> 2  libpthread.so.0 0x00007f020b750cb0
> 3  libc.so.6       0x00007f020a99f425 gsignal + 53
> 4  libc.so.6       0x00007f020a9a2b8b abort + 379
> 5  llc             0x000000000143b1a6
> 6  llc             0x0000000000f3cb02 llvm::TargetPassConfig::addPass(void
> const*) + 146
> 7  llc             0x0000000000f3ddef
> llvm::TargetPassConfig::addCGRegAlloc(llvm::CallGraphSCCPass*) + 47
> 8  llc             0x0000000000f3d7df
> llvm::TargetPassConfig::addMachinePasses() + 719
> 9  llc             0x0000000000e5a3af
> 10 llc             0x0000000000e5994c
> llvm::LLVMTargetMachine::addPassesToEmitFile(llvm::PassManagerBase&,
> llvm::formatted_raw_ostream&, llvm::TargetMachine::CodeGenFileType, bool,
> void const*, void const*) + 92
> 11 llc             0x00000000005f6002 main + 4946
> 12 libc.so.6       0x00007f020a98a76d __libc_start_main + 237
> 13 llc             0x00000000005f4bd1
> Stack dump:
> 0.    Program arguments: llc --debug -cgregalloc=cg
> Aborted (core dumped)
>
> I am not really sure, why it says "Pass ID is not registered". I did quite
> a lot of internet searching about it and whatever I try to look for I end
> up on the exact LLVM line of code which prints this error line. So, I am
> not sure what is going on. Is this because CallGraphSCCPass does not
> register anything with the MachineFunctionPass-es? Or is this because
> CallGraphSCCPass does not do some magic which is specific to CodeGen
> passes? Can you please help me with this a bit? May be some pointers?
>
>
> On Fri, Nov 2, 2012 at 2:03 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk>wrote:
>
>>
>> On Oct 31, 2012, at 1:41 PM, Madhusudan C.S <madhusudancs at gmail.com>
>> wrote:
>>
>> >   I have spent last 4 weeks trying to figure out how to implement
>> > Interprocedural Register Allocation. I must admit that I was really
>> > overwhelmed with LLVM's codebase while trying to figure this out :)
>> > There is so much to know! I think I have reached a point where I
>> > have some sort of basic understanding of what needs to be done,
>> > but I need some help from here on. So here is the summary of
>> > what I know and for what I need more help.
>> >
>> > I see that lib/CodeGen/Passes.cpp adds PrologEpilogInserter (PEI
>> > henceforth) pass after the RegAlloc pass. Do I understand correctly
>> > that LLVM first performs a given pass on all the functions before
>> > moving to the next pass?
>>
>> No, it's the other way around.
>>
>> You may want to read up on the pass manager and play with the -debug-pass
>> option.
>>
>> /jakob
>>
>>
>
>
> --
> Thanks and regards,
>   Madhusudan.C.S
>
>
>


-- 
Thanks and regards,
  Madhusudan.C.S
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