Vectorize all bounds checks for Node256 scan

ConflictSet.cpp

@@ -313,7 +313,7 @@ struct Node256 : Node {
   BitSet bitSet;
   Node *children[256];
   int64_t childMaxVersion[256];
-  constexpr static int kMaxOfMaxPageSize = 8;
+  constexpr static int kMaxOfMaxPageSize = 16;
   constexpr static int kMaxOfMaxShift =
       std::countr_zero(uint32_t(kMaxOfMaxPageSize));
   constexpr static int kMaxOfMaxTotalPages = 256 / kMaxOfMaxPageSize;
@@ -1779,6 +1779,7 @@ bool checkMaxBetweenExclusive(Node *n, int begin, int end,
   }
 
   // [begin, end) is now the half-open interval of children we're interested in.
+  assert(begin < end);
 
   const unsigned shiftUpperBound = end - begin;
   const unsigned shiftAmount = begin;
@@ -1820,36 +1821,67 @@ bool checkMaxBetweenExclusive(Node *n, int begin, int end,
   }
   case Type_Node256: {
     auto *self = static_cast<Node256 *>(n);
-    // Check the first page
-    if (self->maxOfMax[begin >> Node256::kMaxOfMaxShift] > readVersion) {
-      bool result = true;
-      for (int i = 0; i < Node256::kMaxOfMaxPageSize; ++i) {
-        int j = (begin & ~(Node256::kMaxOfMaxPageSize - 1)) + i;
-        result &= !((self->childMaxVersion[j] > readVersion) & inBounds(j));
+    if (end <= 0) {
+      return true;
+    }
+    const int firstPage = begin >> Node256::kMaxOfMaxShift;
+    const int lastPage = (end - 1) >> Node256::kMaxOfMaxShift;
+    if (firstPage == lastPage) {
+      if (self->maxOfMax[firstPage] <= readVersion) {
+        return true;
       }
-      if (!result) {
-        return result;
+      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;
+      conflict >>= intraPageBegin;
+      return !conflict;
+    }
+    // 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 (conflict) {
+        return false;
       }
     }
     // Check the last page
-    if (end >= 1 &&
-        self->maxOfMax[(end - 1) >> Node256::kMaxOfMaxShift] > readVersion) {
-      bool result = true;
+    if (self->maxOfMax[lastPage] > readVersion) {
+      uint64_t conflict = 0;
       for (int i = 0; i < Node256::kMaxOfMaxPageSize; ++i) {
-        int j = ((end - 1) & ~(Node256::kMaxOfMaxPageSize - 1)) + i;
-        result &= !((self->childMaxVersion[j] > readVersion) & inBounds(j));
+        int j = (lastPage << Node256::kMaxOfMaxShift) + i;
+        conflict |= (self->childMaxVersion[j] > readVersion) << i;
       }
-      if (!result) {
-        return result;
+      const int intraPageEnd = end - (lastPage << Node256::kMaxOfMaxShift);
+      conflict &= (1 << intraPageEnd) - 1;
+      if (conflict) {
+        return false;
       }
     }
-    // Check inner pages
-    bool result = true;
-    for (int i = (begin >> Node256::kMaxOfMaxShift) + 1;
-         i < ((end - 1) >> Node256::kMaxOfMaxShift); ++i) {
-      result &= self->maxOfMax[i] <= readVersion;
+    uint64_t conflict = 0;
+    // Check all possible inner pages
+    for (int i = 1; i < Node256::kMaxOfMaxTotalPages - 1; ++i) {
+      conflict |= (self->maxOfMax[i] > readVersion) << i;
     }
-    return result;
+    // Only keep inner pages
+    const int innerPageBegin = (begin >> Node256::kMaxOfMaxShift) + 1;
+    const int innerPageEnd = (end - 1) >> Node256::kMaxOfMaxShift;
+    conflict &= (1 << innerPageEnd) - 1;
+    conflict >>= innerPageBegin;
+    return !conflict;
   }
   default:                   // GCOVR_EXCL_LINE
     __builtin_unreachable(); // GCOVR_EXCL_LINE