Simplify arena_slab_regind().

Rewrite arena_slab_regind() to provide sufficient constant data for
the compiler to perform division strength reduction.  This replaces
more general manual strength reduction that was implemented before
arena_bin_info was compile-time-constant.  It would be possible to
slightly improve on the compiler-generated division code by taking
advantage of range limits that the compiler doesn't know about.

include/jemalloc/internal/arena.h

@@ -271,6 +271,9 @@ void	arena_extent_cache_maybe_insert(tsdn_t *tsdn, arena_t *arena,
     extent_t *extent, bool cache);
 void	arena_extent_cache_maybe_remove(tsdn_t *tsdn, arena_t *arena,
     extent_t *extent, bool cache);
+#ifdef JEMALLOC_JET
+size_t	arena_slab_regind(extent_t *slab, szind_t binind, const void *ptr);
+#endif
 extent_t	*arena_extent_alloc_large(tsdn_t *tsdn, arena_t *arena,
     size_t usize, size_t alignment, bool *zero);
 void	arena_extent_dalloc_large(tsdn_t *tsdn, arena_t *arena,

include/jemalloc/internal/private_symbols.txt

@@ -66,6 +66,7 @@ arena_ralloc_no_move
 arena_reset
 arena_salloc
 arena_sdalloc
+arena_slab_regind
 arena_stats_merge
 arena_tcache_fill_small
 arena_tdata_get