From 2721728c9056b442c0281f20792f19eb6a491aa0 Mon Sep 17 00:00:00 2001
From: Lars Knoll <lars.knoll@qt.io>
Date: Wed, 25 Nov 2020 11:36:24 +0100
Subject: [PATCH] Optimize code in QTaggedPointer

Don't execute instructions that will never do anything.

Directly add the tag to the pointer in the constructor to avoid
additional masking operations, and avoid a masking op that is in
practice a no-op in setTag().

Do the same optimization in QTagPreservingPointerToPointer.

Pick-to: dev
Change-Id: Ia364f89cbe6ccc876ec9bda0c239fc4f57c10501
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 src/corelib/kernel/qpropertyprivate.h |  2 +-
 src/corelib/tools/qtaggedpointer.h    | 11 +++++------
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/src/corelib/kernel/qpropertyprivate.h b/src/corelib/kernel/qpropertyprivate.h
index 0edfe5781b7..91d9e56d2f0 100644
--- a/src/corelib/kernel/qpropertyprivate.h
+++ b/src/corelib/kernel/qpropertyprivate.h
@@ -283,7 +283,7 @@ public:
 
     void setPointer(T *ptr)
     {
-        *d = (reinterpret_cast<quintptr>(ptr) & QTaggedPointer<T, Tag>::pointerMask()) | (*d & QTaggedPointer<T, Tag>::tagMask());
+        *d = reinterpret_cast<quintptr>(ptr) | (*d & QTaggedPointer<T, Tag>::tagMask());
     }
 
     T *get() const
diff --git a/src/corelib/tools/qtaggedpointer.h b/src/corelib/tools/qtaggedpointer.h
index 819ebb2387c..f6ce85eebc3 100644
--- a/src/corelib/tools/qtaggedpointer.h
+++ b/src/corelib/tools/qtaggedpointer.h
@@ -83,14 +83,13 @@ public:
     constexpr QTaggedPointer(std::nullptr_t) noexcept : QTaggedPointer() {}
 
     explicit QTaggedPointer(T *pointer, Tag tag = Tag()) noexcept
-        : d(quintptr(pointer))
+        : d(quintptr(pointer) | quintptr(tag))
     {
         static_assert(sizeof(Type*) == sizeof(QTaggedPointer));
 
-        Q_ASSERT_X((quintptr(pointer) & tagMask()) == 0,
-            "QTaggedPointer<T, Tag>", "Pointer is not aligned");
-
-        setTag(tag);
+        Q_ASSERT_X((quintptr(pointer) & tagMask()) == 0, "QTaggedPointer<T, Tag>", "Pointer is not aligned");
+        Q_ASSERT_X((static_cast<typename QtPrivate::TagInfo<T>::TagType>(tag) & pointerMask()) == 0,
+            "QTaggedPointer<T, Tag>::setTag", "Tag is larger than allowed by number of available tag bits");
     }
 
     Type &operator*() const noexcept
@@ -125,7 +124,7 @@ public:
         Q_ASSERT_X((static_cast<typename QtPrivate::TagInfo<T>::TagType>(tag) & pointerMask()) == 0,
             "QTaggedPointer<T, Tag>::setTag", "Tag is larger than allowed by number of available tag bits");
 
-        d = (d & pointerMask()) | (static_cast<typename QtPrivate::TagInfo<T>::TagType>(tag) & tagMask());
+        d = (d & pointerMask()) | static_cast<quintptr>(tag);
     }
 
     Tag tag() const noexcept