[PATCH] [AArch64] Build correct vector filled with undef nodes

[Tim Northover]

Hi David,

> The only disadvantage of my method is we should use ReplaceUndefFromZeroOrOneVector carefully

There's the extra complexity in implementation and tight coupling to isBuildVectorAllOnes as well (if that function was hypothetically enhanced to handle extra cases, this function would break).

> For this small case which is to fix a bug, I think we need not to add 6 getConstantSplat functions.

I agree. We have a real use for at least one though, so we should add it. Otherwise these functions would never appear, no matter how useful they are, as everyone says "it's not worth it just for this one case".

Cheers.

Tim.

http://reviews.llvm.org/D5139