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

[Lang Hames]

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
>>
>>
>>
>>
>
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