[LLVMdev] problem trying to write an LLVM register-allocation pass

[horwitz at cs.wisc.edu]

Lang -

I used addLiveIn and that fixed almost all of the problems with the verify
flag, including the example I sent previously, so no need to look into
that.  I still have a few cases where I'm getting "verify" errors, though
they don't seem to affect the correctness of the final code.  I will send
an example ASAP.

Thanks for all your help!

Susan

> Hi Susan,
>
> Jakob pointed out to me that the Gcra.cpp allocator doesn't record
> basic-block live-ins, which are used by the verifier to check correctness.
>
> You can record which variables are live into a basic block with
> MachineBasicBlock::addLiveIn(unsigned physReg). I don't know the verifier
> well, but if it's using other built in infrastructure for register
> allocation then it may not be a good fit for your allocator.
>
> I'll try to find time to look at the example files you sent in the next
> couple of days.
>
> Cheers,
> Lang.
>
>
> On Thu, Nov 15, 2012 at 5:21 PM, Susan Horwitz <horwitz at cs.wisc.edu>
> wrote:
>
>> Well, now I can't reproduce what I thought I had before (an example that
>> works fine with your code except when using that flag).  I do have a
>> small
>> example that works fine with *my* code except when using that flag.
>> I've
>> attached the source (.c), the assembly that my code produces w/o using
>> the
>> "verify" flag (.s), the output of trying to create assembly *with* the
>> "verify" flag (.out), and the .bc file used as input to my register
>> allocator.  If you can identify a problem by looking at these files,
>> that
>> would be great!
>>
>> I can supply my register allocator if you'd like to have it, but it
>> involves a number of (longish) files.
>>
>> Thanks for any insights you can provide on this!
>>
>> Susan
>>
>>
>>
>> On 11/15/2012 06:45 PM, Lang Hames wrote:
>>
>>> Hi Susan,
>>>
>>> To my knowledge the verifier doesn't produce false positives with any
>>> of
>>> the in-tree allocators. If it is raising an error that is worth
>>> investigating. Is it raising an error on any simple test cases? Can you
>>> share the failing case?
>>>
>>> - Lang.
>>>
>>>
>>> On Thu, Nov 15, 2012 at 2:44 PM, Susan Horwitz <horwitz at cs.wisc.edu
>>> <mailto:horwitz at cs.wisc.edu>> wrote:
>>>
>>>     I tried using this flag and it gave me errors on code that
>>> otherwise
>>>     assembles and runs just fine (using the version of Gcra.cpp that
>>>     Lang wrote).  So I'm wondering if I should really be using the
>>> flag?
>>>       I'm using it like this:
>>>
>>>     llc -verify-machineinstrs -load Debug/lib/P4.so -regalloc=gc xxx.bc
>>>
>>>     Susan
>>>
>>>
>>>
>>>     On 11/15/2012 01:13 PM, Jakob Stoklund Olesen wrote:
>>>
>>>
>>>         On Nov 15, 2012, at 7:53 AM, Susan Horwitz<horwitz at cs.wisc.edu
>>>         <mailto:horwitz at cs.wisc.edu>>
>>>
>>>         wrote:
>>>
>>>             Lang -
>>>
>>>             Attached is a new example for which I still get assembler
>>>             errors.
>>>
>>>             Susan
>>>
>>>
>>>         Hi Susan,
>>>
>>>         You should never be getting assembler errors if 'llc
>>>         -verify-machineinstrs' approves of your machine code. It might
>>> give
>>>         you better error messages than the assembler.
>>>
>>>         /jakob
>>>
>>>
>>>
>>>
>>
>