llvm dev - Apr 2008 - [LLVMdev] MergeInClobberRanges

Why does LiveInterval::MergeInClobberRanges set the definition index
as unknown?  Why would the definition index not be the definition index
for the range merged in from the other interval?  I suppose if two ranges
overlap it's not clear what to set the def index to.  Perhaps it should
result
in two separate ranges with different def indices.

                                                   -Dave

On Apr 2, 2008, at 5:09 PM, David Greene wrote:
> Why does LiveInterval::MergeInClobberRanges set the definition index
> as unknown?  Why would the definition index not be the definition  
> index
> for the range merged in from the other interval?  I suppose if two  
> ranges
> overlap it's not clear what to set the def index to.  Perhaps it  
> should result
> in two separate ranges with different def indices.
Right. The coalescer is being very conservative when it comes to  
dealing with sub- / super- registers so it's not keeping very precise  
information. Feel free to make it better! :-)

Evan
>
>
>                                                   -Dave
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Funny I just ran into a situation where the imprecise information  
inhibits a coalescing. If you have made changes related to this, I'd  
love to have it.

Thanks,

Evan

On Apr 7, 2008, at 10:52 AM, Evan Cheng wrote:
>
> On Apr 2, 2008, at 5:09 PM, David Greene wrote:
>
>> Why does LiveInterval::MergeInClobberRanges set the definition index
>> as unknown?  Why would the definition index not be the definition
>> index
>> for the range merged in from the other interval?  I suppose if two
>> ranges
>> overlap it's not clear what to set the def index to.  Perhaps it
>> should result
>> in two separate ranges with different def indices.
>
> Right. The coalescer is being very conservative when it comes to
> dealing with sub- / super- registers so it's not keeping very precise
> information. Feel free to make it better! :-)
>
> Evan
>
>>
>>
>>                                                  -Dave
>> _______________________________________________
>> 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