QArrayDataOps::assign: simplify undoing the prepend optim. for trivials

Since they are trivial, we don't need to loop destroying anything (dead
code anyway), so help the compiler out and always store the new capacity
begin. This may be storing the value that was already there if no
element was removed from the beginning of the list, but it does remove a
conditional.

Further, this removes the entire looping over the prepend optimization
buffer for new elements. We'll fall straight to the main assignment
loop.

Change-Id: I5338b6a53bffbda17a08fffd1d7eda72d57eff29
Reviewed-by: Fabian Kosmale <[email protected]>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/corelib/tools/qarraydataops.h b/src/corelib/tools/qarraydataops.h
index 4a5926a7056..c6259354de9 100644
--- a/src/corelib/tools/qarraydataops.h
+++ b/src/corelib/tools/qarraydataops.h
@@ -962,7 +962,12 @@ public:
             capacityBegin = Data::dataStart(this->d, alignof(typename Data::AlignmentDummy));
             offset = dst - capacityBegin;
         }
-        if (offset) { // avoids dead stores
+        if constexpr (!QTypeInfo<T>::isComplex) {
+            this->setBegin(capacityBegin); // undo prepend optimization
+            dst = capacityBegin;
+
+            // there's nothing to destroy or overwrite
+        } else if (offset) { // avoids dead stores
             T *prependBufferEnd = dst;
             this->setBegin(capacityBegin); // undo prepend optimization
             dst = capacityBegin;