[PATCH] D66095: [InstCombine] canonicalize a scalar-select-of-vectors to vector select

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D66095#1631495 <https://reviews.llvm.org/D66095#1631495>, @spatel wrote:

> In D66095#1630408 <https://reviews.llvm.org/D66095#1630408>, @ABataev wrote:
>
> > What about very long vectors that do no fit into single register? Is it cost effective for such vectors too?
>
>
> We would split the long vectors into values that fit the target registers in the backend. At that point, the target can decide if N vector selects are better or worse than a transfer to scalar compare and branch. As @lebedev.ri mentioned, we're missing that logic in SDAG, but given that this transform produces the better code for the default case, I don't think we need to make this patch dependent on backend fixups.


But it adds extra cost for vectors splitting. Maybe limit the size of the vectors in the patch?


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