More SIMD for scanning Node256 with 32-bit versions

CMakeLists.txt

@@ -59,6 +59,10 @@ cmake_pop_check_state()
 
 option(USE_SIMD_FALLBACK
        "Use fallback implementations of functions that use SIMD" OFF)
+option(
+  USE_32_BIT_VERSIONS,
+  "Store 32 bit versions internally, and rely on versions never being different by more than 2e9"
+  OFF)
 
 # This is encouraged according to
 # https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq
@@ -103,6 +107,10 @@ if(NOT USE_SIMD_FALLBACK)
   endif()
 endif()
 
+if(USE_32_BIT_VERSIONS)
+  add_compile_definitions(INTERNAL_VERSION_32_BIT=1)
+endif()
+
 set(CMAKE_CXX_IMPLICIT_LINK_LIBRARIES "")
 
 add_library(${PROJECT_NAME}-object OBJECT ConflictSet.cpp)

ConflictSet.cpp

@@ -72,7 +72,9 @@ constexpr void removeKey(struct Node *) {}
 
 // ==================== BEGIN IMPLEMENTATION ====================
 
+#ifndef INTERNAL_VERSION_32_BIT
 #define INTERNAL_VERSION_32_BIT 0
+#endif
 
 #if INTERNAL_VERSION_32_BIT
 struct InternalVersionT {
@@ -582,9 +584,14 @@ std::string getSearchPath(Node *n);
 
 // Each node with an entry present gets a budget of kBytesPerKey. Node0 always
 // has an entry present.
-constexpr int kBytesPerKey = 144;
 // Induction hypothesis is that each node's surplus is >= kMinNodeSurplus
+#if INTERNAL_VERSION_32_BIT
+constexpr int kBytesPerKey = 112;
+constexpr int kMinNodeSurplus = 80;
+#else
+constexpr int kBytesPerKey = 144;
 constexpr int kMinNodeSurplus = 104;
+#endif
 constexpr int kMinChildrenNode3 = 2;
 constexpr int kMinChildrenNode16 = 4;
 constexpr int kMinChildrenNode48 = 17;
@@ -1759,10 +1766,12 @@ downLeftSpine:
   }
 }
 
-// Returns true if all in-bounds vs are <= readVersion
+// Returns true if v[i] <= readVersion for all i such that begin <= is[i] < end
+// Preconditions: begin <= end, end - begin < 256
 bool scan16(const InternalVersionT *vs, const uint8_t *is, int begin, int end,
             InternalVersionT readVersion) {
 
+  assert(begin <= end);
   assert(end - begin < 256);
 
 #ifdef HAS_ARM_NEON
@@ -1781,13 +1790,14 @@ bool scan16(const InternalVersionT *vs, const uint8_t *is, int begin, int end,
   memcpy(w4, vs, sizeof(w4));
   uint32_t rv;
   memcpy(&rv, &readVersion, sizeof(rv));
+  const auto rvVec = vdupq_n_u32(rv);
 
   int32x4_t z;
   memset(&z, 0, sizeof(z));
 
   uint16x4_t conflicting[4];
   for (int i = 0; i < 4; ++i) {
-    conflicting[i] = vmovn_u32(vcgtq_s32(vsubq_u32(w4[i], vdupq_n_u32(rv)), z));
+    conflicting[i] = vmovn_u32(vcgtq_s32(vsubq_u32(w4[i], rvVec), z));
   }
   auto combined =
       vcombine_u8(vmovn_u16(vcombine_u16(conflicting[0], conflicting[1])),
@@ -1837,6 +1847,48 @@ bool scan16(const InternalVersionT *vs, const uint8_t *is, int begin, int end,
 #endif
 }
 
+// Returns true if v[i] <= readVersion for all i such that begin <= i < end
+bool scan16(const InternalVersionT *vs, int begin, int end,
+            InternalVersionT readVersion) {
+  assert(0 <= begin && begin < 16);
+  assert(0 <= end && end <= 16);
+  assert(begin <= end);
+
+#if INTERNAL_VERSION_32_BIT && defined(HAS_ARM_NEON)
+  uint32x4_t w4[4];
+  memcpy(w4, vs, sizeof(w4));
+  uint32_t rv;
+  memcpy(&rv, &readVersion, sizeof(rv));
+  const auto rvVec = vdupq_n_u32(rv);
+
+  int32x4_t z;
+  memset(&z, 0, sizeof(z));
+
+  uint16x4_t conflicting[4];
+  for (int i = 0; i < 4; ++i) {
+    conflicting[i] = vmovn_u32(vcgtq_s32(vsubq_u32(w4[i], rvVec), z));
+  }
+  auto combined =
+      vcombine_u8(vmovn_u16(vcombine_u16(conflicting[0], conflicting[1])),
+                  vmovn_u16(vcombine_u16(conflicting[2], conflicting[3])));
+
+  uint64_t conflict = vget_lane_u64(
+      vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(combined), 4)), 0);
+
+  conflict &= end == 16 ? -1 : (uint64_t(1) << (end << 2)) - 1;
+  conflict >>= begin << 2;
+  return !conflict;
+#else
+  uint64_t conflict = 0;
+  for (int i = 0; i < 16; ++i) {
+    conflict |= (vs[i] > readVersion) << i;
+  }
+  conflict &= (1 << end) - 1;
+  conflict >>= begin;
+  return !conflict;
+#endif
+}
+
 // Return whether or not the max version among all keys starting with the search
 // path of n + [child], where child in (begin, end) is <= readVersion. Does not
 // account for the range version of firstGt(searchpath(n) + [end - 1])
@@ -1907,68 +1959,45 @@ bool checkMaxBetweenExclusive(Node *n, int begin, int end,
     return true;
   }
   case Type_Node256: {
+    static_assert(Node256::kMaxOfMaxTotalPages == 16);
     auto *self = static_cast<Node256 *>(n);
     if (end <= 0) {
       return true;
     }
     const int firstPage = begin >> Node256::kMaxOfMaxShift;
     const int lastPage = (end - 1) >> Node256::kMaxOfMaxShift;
+    // Check the only page if there's only one
     if (firstPage == lastPage) {
       if (self->maxOfMax[firstPage] <= readVersion) {
         return true;
       }
-      uint64_t conflict = 0;
-      // Check all in page
-      for (int i = 0; i < Node256::kMaxOfMaxPageSize; ++i) {
-        conflict |=
-            (self->childMaxVersion[(firstPage << Node256::kMaxOfMaxShift) + i] >
-             readVersion)
-            << i;
-      }
-      // Mask away out of bounds
       const int intraPageBegin = begin & (Node256::kMaxOfMaxPageSize - 1);
       const int intraPageEnd = end - (lastPage << Node256::kMaxOfMaxShift);
-      conflict &= (1 << intraPageEnd) - 1;
+      return scan16(self->childMaxVersion +
-      conflict >>= intraPageBegin;
+                        (firstPage << Node256::kMaxOfMaxShift),
-      return !conflict;
+                    intraPageBegin, intraPageEnd, readVersion);
     }
     // Check the first page
     if (self->maxOfMax[firstPage] > readVersion) {
-      uint64_t conflict = 0;
-      for (int i = 0; i < Node256::kMaxOfMaxPageSize; ++i) {
-        int j = (firstPage << Node256::kMaxOfMaxShift) + i;
-        conflict |= (self->childMaxVersion[j] > readVersion) << i;
-      }
       const int intraPageBegin = begin & (Node256::kMaxOfMaxPageSize - 1);
-      conflict >>= intraPageBegin;
+      if (!scan16(self->childMaxVersion +
-      if (conflict) {
+                      (firstPage << Node256::kMaxOfMaxShift),
+                  intraPageBegin, 16, readVersion)) {
         return false;
       }
     }
     // Check the last page
     if (self->maxOfMax[lastPage] > readVersion) {
-      uint64_t conflict = 0;
-      for (int i = 0; i < Node256::kMaxOfMaxPageSize; ++i) {
-        int j = (lastPage << Node256::kMaxOfMaxShift) + i;
-        conflict |= (self->childMaxVersion[j] > readVersion) << i;
-      }
       const int intraPageEnd = end - (lastPage << Node256::kMaxOfMaxShift);
-      conflict &= (1 << intraPageEnd) - 1;
+      if (!scan16(self->childMaxVersion + (lastPage << Node256::kMaxOfMaxShift),
-      if (conflict) {
+                  0, intraPageEnd, readVersion)) {
         return false;
       }
     }
-    uint64_t conflict = 0;
+    // Check inner pages
-    // Check all possible inner pages
-    for (int i = 1; i < Node256::kMaxOfMaxTotalPages - 1; ++i) {
-      conflict |= (self->maxOfMax[i] > readVersion) << i;
-    }
-    // Only keep inner pages
     const int innerPageBegin = (begin >> Node256::kMaxOfMaxShift) + 1;
     const int innerPageEnd = (end - 1) >> Node256::kMaxOfMaxShift;
-    conflict &= (1 << innerPageEnd) - 1;
+    return scan16(self->maxOfMax, innerPageBegin, innerPageEnd, readVersion);
-    conflict >>= innerPageBegin;
-    return !conflict;
   }
   default:                   // GCOVR_EXCL_LINE
     __builtin_unreachable(); // GCOVR_EXCL_LINE

Jenkinsfile

@@ -59,6 +59,17 @@ pipeline {
                 CleanBuildAndTest("-DUSE_SIMD_FALLBACK=ON")
             }
         }
+        stage('32-bit versions') {
+            agent {
+                dockerfile {
+                    args '-v /home/jenkins/ccache:/ccache'
+                    reuseNode true
+                }
+            }
+            steps {
+                CleanBuildAndTest("-DUSE_32_BIT_VERSIONS=ON")
+            }
+        }
         stage('Release [gcc]') {
             agent {
                 dockerfile {