[PATCH] D56875: [DAGCombiner] narrow vector binop with 2 insert subvector operands

[Sanjay Patel via Phabricator via llvm-commits]

spatel planned changes to this revision.
spatel added a comment.

Actually, this patch isn't correct as-is. We can't insert into an undef base vector because at least 'xor undef, undef --> 0' (not undef). 
I know I avoided or fixed the similar problem in IR somewhere along the way.
We need to actually compute the constant vector for the specified binop's opcode.


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  https://reviews.llvm.org/D56875/new/

https://reviews.llvm.org/D56875