Revert "Refine {QString, QBA}::reallocData() logic"

This reverts commit 504972f838761f79a170c22225add496e7e5af6a.

Introduced realloc failures in qdoc.

Task-number: QTBUG-88258
Change-Id: I953e8d3933085022c75068af357ec9a44ab7e984
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 13 insertions, 14 deletions

diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index c482e2335e..f4ade684a0 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -1708,11 +1708,12 @@ void QByteArray::reallocData(qsizetype alloc, QArrayData::AllocationOption optio
         return;
     }
 
-    // don't use reallocate path when reducing capacity and there's free space
-    // at the beginning: might shift data pointer outside of allocated space
-    const bool cannotUseReallocate = d.freeSpaceAtBegin() > 0 && alloc < d.constAllocatedCapacity();
+    // there's a case of slow reallocate path where we need to memmove the data
+    // before a call to ::realloc(), meaning that there's an extra "heavy"
+    // operation. just prefer ::malloc() branch in this case
+    const bool slowReallocatePath = d.freeSpaceAtBegin() > 0;
 
-    if (d->needsDetach() || cannotUseReallocate) {
+    if (d->needsDetach() || slowReallocatePath) {
         DataPointer dd(Data::allocate(alloc, option), qMin(alloc, d.size));
         if (dd.size > 0)
             ::memcpy(dd.data(), d.data(), dd.size);
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index eed98e7c7e..32e5bb7b20 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -2504,11 +2504,12 @@ void QString::reallocData(qsizetype alloc, QArrayData::AllocationOption option)
         return;
     }
 
-    // don't use reallocate path when reducing capacity and there's free space
-    // at the beginning: might shift data pointer outside of allocated space
-    const bool cannotUseReallocate = d.freeSpaceAtBegin() > 0 && alloc < d.constAllocatedCapacity();
+    // there's a case of slow reallocate path where we need to memmove the data
+    // before a call to ::realloc(), meaning that there's an extra "heavy"
+    // operation. just prefer ::malloc() branch in this case
+    const bool slowReallocatePath = d.freeSpaceAtBegin() > 0;
 
-    if (d->needsDetach() || cannotUseReallocate) {
+    if (d->needsDetach() || slowReallocatePath) {
         DataPointer dd(Data::allocate(alloc, option), qMin(alloc, d.size));
         if (dd.size > 0)
             ::memcpy(dd.data(), d.data(), dd.size * sizeof(QChar));
diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index e73dc35810..2bf3e9bacc 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -233,13 +233,10 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer,
 {
     Q_ASSERT(!data || !data->isShared());
 
-    const qsizetype headerSize = sizeof(QArrayData);
+    qsizetype headerSize = sizeof(QArrayData);
     qsizetype allocSize = calculateBlockSize(capacity, objectSize, headerSize, option);
-    const qptrdiff offset = dataPointer
-            ? reinterpret_cast<char *>(dataPointer) - reinterpret_cast<char *>(data)
-            : headerSize;
+    qptrdiff offset = dataPointer ? reinterpret_cast<char *>(dataPointer) - reinterpret_cast<char *>(data) : headerSize;
     Q_ASSERT(offset > 0);
-    Q_ASSERT(offset <= allocSize); // == when all free space is at the beginning
 
     allocSize = reserveExtraBytes(allocSize);
     if (Q_UNLIKELY(allocSize < 0))  // handle overflow. cannot reallocate reliably
@@ -247,7 +244,7 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer,
 
     QArrayData *header = static_cast<QArrayData *>(::realloc(data, size_t(allocSize)));
     if (header) {
-        header->alloc = capacity;
+        header->alloc = uint(capacity);
         dataPointer = reinterpret_cast<char *>(header) + offset;
     } else {
         dataPointer = nullptr;