[PATCH] D59626: Add MachineDCE pass after RenameIndependentSubregs

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added a comment.

In D59626#1454322 <https://reviews.llvm.org/D59626#1454322>, @qcolombet wrote:

> Hi @rampitec,
>
> Are the dead instructions marked during the detect dead lanes pass or during the rename independent SubReg pass?
>
> I would expect the former and in that case, it may be easier to just do the code deletion there.
>
> Cheers,
> -Quentin


The detect dead lanes pass cannot really delete dead lanes, just mark them. So a subreg definition becomes dead, but in most cases retain a use by REG_SEQUENCE.
Rename independent subregs deletes REQ_SEQENCEs and the subreg looses that use, so finally can be deleted.

I.e. both passes can free up new dead instructions independently, but in most cases they need to work together.


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