[PATCH] D36224: [TwoAddressInstructionPass] Replace subregister uses when processing tied operands

[Krzysztof Parzyszek via llvm-commits]

On 9/27/2018 11:50 AM, Matthias Braun via Phabricator wrote:
> No! dead, killed and undef are specifically not about the subregister part but about the full vreg. (In an ideal world for subregister liveness we would have a lanemask for dead,killed,undef instead of just the bit we have today. With only a bit available we mostly ignore them for subreg liveness purposes as we cannot express situations like a write with only some lanes dead anyway...)

I was the one doing the "telling" if I remember correctly.

When it comes to verification, why would there be any reason to treat 
dead and kill flags as applying to the full vreg when they are specified 
on a subreg?  We don't need lane masks for that, since the subreg 
relationship is sufficient.

-Krzysztof

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