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The implementation makes use of the freedom added by LWG 3410. We have two variants of this algorithm: * a fast path for random access iterators: This fast path computes the maximum number of loop iterations up-front and does not compare the iterators against their limits on every loop iteration. * A basic implementation for all other iterators: This implementation compares the iterators against their limits in every loop iteration. However, it still takes advantage of the freedom added by LWG 3410 to avoid unnecessary additional iterator comparisons, as originally specified by P1614R2. https://godbolt.org/z/7xbMEen5e shows the benefit of the fast path: The hot loop generated of `lexicographical_compare_three_way3` is more tight than for `lexicographical_compare_three_way1`. The added benchmark illustrates how this leads to a 30% - 50% performance improvement on integer vectors. Implements part of P1614R2 "The Mothership has Landed" Fixes LWG 3410 and LWG 3350 Differential Revision: https://reviews.llvm.org/D131395