[PATCH] [AArch64] Fix a build_vector pattern fail caused by defect in isBuildVectorAllZeros().

[Tim Northover]

Hi Kevin,

Isn't this patch just hiding the backend issue? Enhancing isBuildVectorAllZeros like that seems like a good idea, but I can't see any guarantee that the problematic DAG can't still emerge by some other means (not that my quick tests have managed to produce it).

Cheers.

Tim.

http://reviews.llvm.org/D4228