Introduce QADP::reallocateGrow()

Added realloc() code path to QMovableArrayOps

Implemented fast realloc() based growing for QADP and used it in
QList::emplaceBack. This gives quite a bit of speedup and shows better
results than 5.15 at 100k+ iterations of "list.append(elem)", meanwhile
also closing a gap between movable types

Task-number: QTBUG-87330
Change-Id: I42fc182ecd93c85600dac622385152fc57735da8
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index 3217e87cc8..2bf3e9bacc 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -236,6 +236,7 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer,
     qsizetype headerSize = sizeof(QArrayData);
     qsizetype allocSize = calculateBlockSize(capacity, objectSize, headerSize, option);
     qptrdiff offset = dataPointer ? reinterpret_cast<char *>(dataPointer) - reinterpret_cast<char *>(data) : headerSize;
+    Q_ASSERT(offset > 0);
 
     allocSize = reserveExtraBytes(allocSize);
     if (Q_UNLIKELY(allocSize < 0))  // handle overflow. cannot reallocate reliably
@@ -245,6 +246,8 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer,
     if (header) {
         header->alloc = uint(capacity);
         dataPointer = reinterpret_cast<char *>(header) + offset;
+    } else {
+        dataPointer = nullptr;
     }
     return qMakePair(static_cast<QArrayData *>(header), dataPointer);
 }