With all the preparations made so far it's now possible to implement
the avx-powered search in an array.
The array to search in has both -- capacity and size, so searching in
it needs to take allocated, but unused tail into account. Two options
for that -- limit the number of comparisons "by hands" or keep minimal
and impossible value in this tail, scan "capacity" elements, then
correct the result with "size" value. The latter approach is up to 50%
faster than any (tried) attempt to do the former one.
The run-time selection of the array search code is done with the gnu
target attribute. It's available since gcc 4.8. For AVX-less platforms
the default linear scanner is used.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
If the key type is int64_t and the less-comparator is "natural" (i.e. it's
literally 'a < b') we may use the SIMD instructions to search for the key
on a node. Before doing so, the maybe_key and the searcher should be prepared
for that, in particular:
1. maybe_key should set unused keys to the minimal value
2. the searcher for this case should call the gt() helper with
primitive types -- int64_t search key and array of int64_t values
To tell to B+ code that the key-less pair is such the less-er should define
the simplify_key() method converting search keys to int64_t-s.
This searcher is selected automatically, if any mismatch happens it silently
falls back to default one. Thus also add a static assertion to the row-cache
to mitigate this.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
