[llvm-dev] Print Register Liveness Information

[Quentin Colombet via llvm-dev]

Good point!
Additionally this might gets invalidated by some passes (look for MachineRegisterInfo::invalidateLiveness)

> On Feb 16, 2017, at 2:32 PM, Matthias Braun <mbraun at apple.com> wrote:
> 
> Note that this only works for targets that say TargetRegisterInfo::trackLivenessAfterRegAlloc()== true.
> 
>> On Feb 16, 2017, at 1:21 PM, Quentin Colombet via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
>> Hi Anitha,
>> 
>> The liveness information is usually dropped after regalloc.
>> Therefore the short answer is no, this information is not available before producing assembly.
>> 
>> However, we have the live-ins and you can request the kill flag to be set. From both this information, you can recompute the liveness.
>> I’d suggest you use the LivePhysReg helper class and use its result to annotate your assembly (emitComment or something along those lines).
>> 
>> Cheers,
>> -Quentin
>>> On Feb 16, 2017, at 12:46 PM, Anitha B Gollamudi via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>> 
>>> Hi,
>>> 
>>> Is there a way to print the register liveness information into the assembly file or as some intermediate listing?
>>> To be more precise, I am looking at figuring out the following information in an assembly file/listing.
>>> 
>>> Say, for simplicity, our register set is only { rsp, rbp, eax }
>>> 
>>> 
>>> subq    $16, %rsp     // rsp is killed here, eax and rbp are live
>>> movl    $0, -4(%rbp)  // rbp is killed here, rsp and eax are live
>>> xorl    %eax, %eax    // eax is killed here, rsp and rbp are live
>>> movl    $1, %eax   // eax is killed here, rsp and rbp are live
>>> 
>>> Is there a way LLVM stores this information somewhere before producing assembly?
>>> I haven't  dug into the source code yet, but intuitively the information must be there and hence maybe some pass dumps that info?
>>> 
>>> Thanks!
>>> 
>>>  Anitha
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