[llvm-dev] Liveness of virtual registers
Matthias Braun via llvm-dev
llvm-dev at lists.llvm.org
Thu Jul 28 14:10:15 PDT 2016
> On Jul 28, 2016, at 2:01 PM, Matthias Braun via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> On Jul 28, 2016, at 1:52 PM, Krzysztof Parzyszek <kparzysz at codeaurora.org> wrote:
>> On 7/28/2016 3:49 PM, Matthias Braun wrote:
>>> The isDead and isUndef flags however are required to be correct.
>> Undef yes, but what relies on isDead being accurate (before live interval computation)?
> I only remember Andy/Quentin making those conservative correctness claims about the kill flags but not the dead/undef flags. I am also pretty sure the RegisterPressure.cpp / -verify-misched fail on missing dead flags (although -verify-misched fails in several instances anyway at the moment...)
I re-checked the RegisterPressure.cpp code as well and it does not rely on dead-flags either (if there is no dead flag it queries the liveinterval for it). So it seems you are right with the statement of dead flags being optional.
More information about the llvm-dev