[llvm] [X86][LoopVectorize] Enable MaximizeBandwidth by default on X86 (PR #201666)

[Sumukh J Bharadwaj via llvm-commits]

amd-subharad wrote:

@fhahn perf data is now in the description. On znver4 (single-copy, ref) MaxBW standalone is net-neutral across the rate suites (CPU2026 +0.8% / CPU2017 −0.1% suite means, per-benchmark movement within noise). The real wins are narrow-integer partial-reduction loops once #205373 lands (e.g. 772.marian_r **+10.5%**, 706.stockfish_r **+2.8%** on top of it). Happy to add another uarch if useful.

https://github.com/llvm/llvm-project/pull/201666