[llvm-dev] Print Register Liveness Information

Matthias Braun via llvm-dev llvm-dev at lists.llvm.org
Thu Feb 16 14:32:37 PST 2017

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> 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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