[LLVMdev] Liveness information still usable after register allocation?

[Iain Sandoe]

On 21 Aug 2014, at 17:11, Jonathan Roelofs wrote:

> 
> 
> On 8/21/14, 9:54 AM, Alex S wrote:
>> Hi all,
>> 
>> Sorry to bother those not interested in this problem.
>> 
>> I have a problem while I want to reuse the liveness information after register
>> allocation.
>> When I use the livein_begin() from MachineBasicBlock to get the live-in
>> registers after
>> register alloction. I found that the liveness information is sometime incorrect.
>> For example,
>> some registers should be live-in to the machine basic block as these registers
>> are upward exposed
>> in this machine basic block.
>> 
>> Therefore, I wonder whether there are any liveness analysis available after
>> register allocation.
>> Or, did I misunderstand it?
> I was looking for post-RA liveness the other day and ran into: MachineBasicBlock::computeRegisterLiveness, does it do what you want?
> 
> The neighborhood thing seemed a bit wonky for what I needed at the time, so I didn't end up using it, and in turn pursued a different solution to my problem that didn't need post-RA liveness (I'd need the neighborhood to be the whole basic block, and that seemed a bit awkward).

you might also want to look at TargetRegisterInfo::trackLivenessAfterRegAlloc().
Iain

> 
> HTH,
> 
> Jon
>> 
>> Thanks,
>> Alex
>> 
>> 
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> 
> -- 
> Jon Roelofs
> jonathan at codesourcery.com
> CodeSourcery / Mentor Embedded
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