[llvm-dev] Liveness of virtual registers

[Matthias Braun via llvm-dev]

> 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...)

On the other hand I just checked the MachineVerifier which indeed only checks for sonervatively correct dead flags as you say and I can't think of other places being problematic with missing dead flags.
I wonder if that is by accident or by design.

- Matthias