[AArch64] fold 'isPositive' vector integer operations (PR26819)
This is one of the cases shown in:
https://llvm.org/bugs/show_bug.cgi?id=26819
Shift and negate is what InstCombine prefers to produce (and I tried to make it do more of that
in http://reviews.llvm.org/rL262424 ), so we should recognize that pattern as something that might
come from autovectorization even if it's unlikely to be produced from C NEON intrinsics.
The patch is based on the x86 equivalent:
http://reviews.llvm.org/rL262036
Differential Revision: http://reviews.llvm.org/D17834
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262623
91177308-0d34-0410-b5e6-
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