[AArch64][SVE] Add a pass for SVE intrinsic optimisations

[AArch64][SVE] Add a pass for SVE intrinsic optimisations

Summary:
Creates the SVEIntrinsicOpts pass. In this patch, the pass tries
to remove unnecessary reinterpret intrinsics which convert to
and from svbool_t (llvm.aarch64.sve.convert.[to|from].svbool)

For example, the reinterprets below are redundant:

  %1 = call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv4i1(<vscale x 4 x i1> %a)
  %2 = call <vscale x 4 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv4i1(<vscale x 16 x i1> %1)

The pass also looks for ptest intrinsics and phi instructions where
the operands are being needlessly converted to and from svbool_t.

Reviewers: sdesmalen, andwar, efriedma, cameron.mcinally, c-rhodes, rengolin

Reviewed By: efriedma

Subscribers: mgorny, tschuett, kristof.beyls, hiraditya, rkruppe, psnobl, danielkiss, cfe-commits, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76078