Summary:
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/5620
**TL;DR:** Eight SIMD kernel tests never ran, and two byte-domain kernels trust their caller. This change makes three fixes:
1. **Six tests never compiled.** `test_rabitq_simd.cpp` hides them behind `COMPILE_SIMD_*` macros that the faiss target does not export.
2. **Two tests skipped themselves in a static build.** `TestSQByteDirectAcrossSIMDLevels` needs `SIMDLevel::NONE` as a reference, and a static build does not report that level.
3. **The byte kernels never test their dimension requirement.** `DistanceComputerByte` and `DistanceComputerByteSigned` read 16 bytes per loop step.
## 1. Six tests never compiled
`test_rabitq_simd.cpp` wraps two blocks in `#ifdef COMPILE_SIMD_AVX2` and `#ifdef COMPILE_SIMD_AVX512`. The faiss target sets those macros as `preprocessor_flags`, and it does not export them. A test translation unit never sees them. So the preprocessor deleted both blocks. The file holds nine tests and ran three.
The AVX2 block loses its guard, because every x86 faiss build holds the AVX2 kernels. Its three tests also lose an `#ifdef FAISS_ENABLE_DD` around a runtime skip, which the same problem disabled. `is_simd_level_available()` reports the right answer in a static build too.
The AVX512 block moves to a dynamic dispatch target. A static x86 build compiles the AVX2 kernels only, so the test fails to link there rather than skips. `test_rabitq_simd_vpopcnt.cpp` becomes `test_rabitq_simd_dd.cpp`, because it now holds every RaBitQ test that a static build cannot link. A new `test_rabitq_simd_util.h` holds the scalar reference that both files call.
## 2. Two tests skipped themselves in a static build
`TestSQByteDirectAcrossSIMDLevels` measured the index a second time at `SIMDLevel::NONE`, then compared the two runs. A static build reports only the level it compiles, and omits `NONE`, so both tests skipped.
The tests now compute the distances from the definition. The distances are integers, so the reference is exact. The tests check absolute values now, instead of the agreement of two faiss paths.
## 3. The byte kernels trust the caller
`DistanceComputerByte` and `DistanceComputerByteSigned` read 16 bytes per loop step, so they require `d % 16 == 0`. `sq-dispatch.h` enforces that, and no other caller builds them.
A caller that ignores the requirement reads up to 15 bytes past each code and returns a wrong distance. Each constructor now tests the requirement and throws. The AVX2 and the ARM_NEON specializations both get the test.
Reviewed By: alibeklfc
Differential Revision: D119545379
fbshipit-source-id: ddfdcc30d3662f469b2ec3dbb9d5b9f4dafa21aa
Michael Norris
b5a14632a6