Remove bare simdlib type aliases from simdlib_dispatch.h (#5069)

Summary:
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/5069

Remove the 10 global bare-name using declarations (simd16uint16,
simd32uint8, simd8uint32, simd8float32, simd256bit, simd512bit,
simd32uint16, simd64uint8, simd16float32) from simdlib_dispatch.h.

These aliases resolved through SINGLE_SIMD_LEVEL which is NONE in DD
mode, creating a trap where per-ISA TU code accidentally uses scalar
emulation. Each file that needs the aliases now declares its own using
with an explicit SIMD level, making the dependency visible.

Behavior-preserving: all files use the same SINGLE_SIMD_LEVEL they
used before, but now explicitly.

Reviewed By: mdouze

Differential Revision: D100033901

fbshipit-source-id: 2db034c2868de275a5f018d886264762776548c5

faiss/IndexIVFPQFastScan.cpp

@@ -190,6 +190,9 @@ void IndexIVFPQFastScan::encode_vectors(
  * Look-Up Table functions
  *********************************************************/
 
+// Explicit SIMD-level alias (no global bare aliases).
+using simd8float32 = simd8float32_tpl<SINGLE_SIMD_LEVEL_256>;
+
 void fvec_madd_simd(
         size_t n,
         const float* a,

faiss/IndexIVFRaBitQFastScan.h

@@ -213,6 +213,9 @@ IVFRaBitQHeapHandler<C, SL>::IVFRaBitQHeapHandler(
     }
 }
 
+// Explicit alias — must match SIMDResultHandler::handle() signature.
+using simd16uint16 = simd16uint16_tpl<SINGLE_SIMD_LEVEL_256>;
+
 template <class C, SIMDLevel SL>
 void IVFRaBitQHeapHandler<C, SL>::handle(
         size_t q,

faiss/impl/fast_scan/kernels_simd256.h

@@ -11,6 +11,10 @@
 
 namespace faiss {
 
+// Explicit SIMD-level aliases for this file (no global bare aliases).
+using simd16uint16 = simd16uint16_tpl<SINGLE_SIMD_LEVEL_256>;
+using simd32uint8 = simd32uint8_tpl<SINGLE_SIMD_LEVEL_256>;
+
 /*
  * Multi-BB variant: accumulates NQ queries x BB*32 database elements.
  * Used by the search_1 path (bbs > 32).

faiss/impl/fast_scan/kernels_simd512.h

@@ -14,6 +14,10 @@
 
 namespace faiss {
 
+// Explicit SIMD-level aliases for this file (no global bare aliases).
+using simd32uint16 = simd32uint16_tpl<SINGLE_SIMD_LEVEL_512>;
+using simd64uint8 = simd64uint8_tpl<SINGLE_SIMD_LEVEL_512>;
+
 // NQ=1 specialization: processes 512-bit chunks aggressively.
 // a special version for NQ=1.
 // Despite the function being large in the text form, it compiles to a very

faiss/impl/fast_scan/simd_result_handlers.h

@@ -83,6 +83,9 @@ inline void for_each_block(
 
 } // namespace
 
+// Explicit SIMD-level alias for the virtual interface below.
+using simd16uint16 = simd16uint16_tpl<SINGLE_SIMD_LEVEL_256>;
+
 struct SIMDResultHandler {
     // used to dispatch templates
     bool is_CMax = false;

faiss/impl/simdlib/simdlib_dispatch.h

@@ -38,23 +38,7 @@
 
 #endif
 
-// Convenience aliases: bare names resolve to the current TU's SIMD level.
-// Generic code uses SINGLE_SIMD_LEVEL (= NONE in DD, compiled-in in static).
-// Per-SIMD TUs should define their own aliases with the concrete level.
-
-namespace faiss {
-
-// 256-bit
-using simd256bit = simd256bit_tpl<SINGLE_SIMD_LEVEL_256>;
-using simd16uint16 = simd16uint16_tpl<SINGLE_SIMD_LEVEL_256>;
-using simd32uint8 = simd32uint8_tpl<SINGLE_SIMD_LEVEL_256>;
-using simd8uint32 = simd8uint32_tpl<SINGLE_SIMD_LEVEL_256>;
-using simd8float32 = simd8float32_tpl<SINGLE_SIMD_LEVEL_256>;
-
-// 512-bit (AVX512_SPR maps to AVX512 — same 512-bit integer ops)
-using simd512bit = simd512bit_tpl<SINGLE_SIMD_LEVEL_512>;
-using simd32uint16 = simd32uint16_tpl<SINGLE_SIMD_LEVEL_512>;
-using simd64uint8 = simd64uint8_tpl<SINGLE_SIMD_LEVEL_512>;
-using simd16float32 = simd16float32_tpl<SINGLE_SIMD_LEVEL_512>;
-
-} // namespace faiss
+// No global bare-name aliases (simd16uint16, simd32uint8, etc.) — each file
+// that needs them must declare its own `using` with an explicit SIMD level.
+// This prevents per-ISA TUs from accidentally picking up SINGLE_SIMD_LEVEL
+// (= NONE in DD mode) when they should use THE_SIMD_LEVEL.

faiss/utils/approx_topk_hamming/approx_topk_hamming.h

@@ -16,6 +16,10 @@
 
 namespace faiss {
 
+// Explicit SIMD-level aliases for this file (no global bare aliases).
+using simd8uint32 = simd8uint32_tpl<SINGLE_SIMD_LEVEL_256>;
+using simd16uint16 = simd16uint16_tpl<SINGLE_SIMD_LEVEL_256>;
+
 // HeapWithBucketsForHamming32 uses simd8uint32 under the
 // hood.
 

tests/test_simdlib.cpp

@@ -11,6 +11,11 @@
 
 using namespace faiss;
 
+// Explicit SIMD-level aliases (no global bare aliases).
+using simd8float32 = simd8float32_tpl<SINGLE_SIMD_LEVEL_256>;
+using simd8uint32 = simd8uint32_tpl<SINGLE_SIMD_LEVEL_256>;
+using simd16uint16 = simd16uint16_tpl<SINGLE_SIMD_LEVEL_256>;
+
 TEST(TestSIMDLib, TestCmpltAndBlendInplace) {
     simd8float32 lowestValues(0, 1, 2, 3, 4, 5, 6, 7);
     simd8uint32 lowestIndices(0, 1, 2, 3, 4, 5, 6, 7);