Add an avx512bw longestCommonPrefix

ConflictSet.cpp

@@ -1673,6 +1673,33 @@ int firstNeqStride(const uint8_t *ap, const uint8_t *bp) {
 #endif
 }
 
+#if defined(__x86_64__) && !defined(__SANITIZE_THREAD__)
+__attribute__((target("avx512bw"))) int
+longestCommonPrefix(const uint8_t *ap, const uint8_t *bp, int cl) {
+  int i = 0;
+  int end = cl & ~63;
+  while (i < end) {
+    const uint64_t eq =
+        _mm512_cmpeq_epi8_mask(_mm512_loadu_epi8(ap), _mm512_loadu_epi8(bp));
+    if (eq != uint64_t(-1)) {
+      return i + std::countr_one(eq);
+    }
+    i += 64;
+    ap += 64;
+    bp += 64;
+  }
+  if (i < cl) {
+    const uint64_t mask = (uint64_t(1) << (cl - i)) - 1;
+    const uint64_t eq = _mm512_cmpeq_epi8_mask(
+        _mm512_maskz_loadu_epi8(mask, ap), _mm512_maskz_loadu_epi8(mask, bp));
+    return i + std::countr_one(eq & mask);
+  }
+  assert(i == cl);
+  return i;
+}
+__attribute__((target("default")))
+#endif
+
 int longestCommonPrefix(const uint8_t *ap, const uint8_t *bp, int cl) {
   assume(cl >= 0);
   int i = 0;