QDuplicateTracker: fix the static buffer size calculation

Instead of just sizeof(T), we, of course, also need to take the
support structure into account, to wit: the bucket list and, in the
node, the next pointer and the stored hash value.

Change-Id: I8227a95c49e316aacf3d4efd8f6170ea3bea1cf0
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 3c88e12beb22d8ea11b8a7006a71ba9773c6d183)

1 files changed, 7 insertions, 1 deletions

diff --git a/src/corelib/tools/qduplicatetracker_p.h b/src/corelib/tools/qduplicatetracker_p.h
index 9a3385620d..ed7053fce9 100644
--- a/src/corelib/tools/qduplicatetracker_p.h
+++ b/src/corelib/tools/qduplicatetracker_p.h
@@ -64,7 +64,13 @@ QT_BEGIN_NAMESPACE
 template <typename T, size_t Prealloc = 32>
 class QDuplicateTracker {
 #ifdef __cpp_lib_memory_resource
-    char buffer[Prealloc * sizeof(T)];
+    struct node_guesstimate { void *next; size_t hash; T value; };
+    static constexpr size_t bufferSize(size_t N) {
+        return N * sizeof(void*) // bucket list
+                + N * sizeof(node_guesstimate); // nodes
+    }
+
+    char buffer[bufferSize(Prealloc)];
     std::pmr::monotonic_buffer_resource res{buffer, sizeof buffer};
     std::pmr::unordered_set<T> set{&res};
 #else