From f43828687581c2d89549225d1cdc7518bde43b65 Mon Sep 17 00:00:00 2001
From: Lars Knoll <lars.knoll@qt.io>
Date: Wed, 4 Nov 2020 11:10:56 +0100
Subject: [PATCH] Implement fast paths for removeFirst() and removeLast()

This avoids lots of the code and checks in remove() making the
methods a lot faster.

Change-Id: If99c39f5b55672b341f9331b5903bf77e9e67477
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/tools/qarraydataops.h | 44 +++++++++++++++++++++++++++++++
 src/corelib/tools/qlist.h         | 22 ++++++++++++++--
 2 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/src/corelib/tools/qarraydataops.h b/src/corelib/tools/qarraydataops.h
index 12d30e6d5d..fc9c5dbe7f 100644
--- a/src/corelib/tools/qarraydataops.h
+++ b/src/corelib/tools/qarraydataops.h
@@ -429,6 +429,19 @@ public:
         this->size -= (e - b);
     }
 
+    void eraseFirst()
+    {
+        Q_ASSERT(this->size);
+        ++this->ptr;
+        --this->size;
+    }
+
+    void eraseLast()
+    {
+        Q_ASSERT(this->size);
+        --this->size;
+    }
+
     void assign(T *b, T *e, parameter_type t)
     {
         Q_ASSERT(b <= e);
@@ -830,6 +843,22 @@ public:
         } while (b != e);
     }
 
+    void eraseFirst()
+    {
+        Q_ASSERT(this->size);
+        this->begin()->~T();
+        ++this->ptr;
+        --this->size;
+    }
+
+    void eraseLast()
+    {
+        Q_ASSERT(this->size);
+        (--this->end())->~T();
+        --this->size;
+    }
+
+
     void assign(T *b, T *e, parameter_type t)
     {
         Q_ASSERT(b <= e);
@@ -1300,6 +1329,21 @@ public:
             Base::erase(GrowsForwardTag{}, b, e);
         }
     }
+
+    void eraseFirst()
+    {
+        Q_ASSERT(this->isMutable());
+        Q_ASSERT(this->size);
+        Base::eraseFirst();
+    }
+
+    void eraseLast()
+    {
+        Q_ASSERT(this->isMutable());
+        Q_ASSERT(this->size);
+        Base::eraseLast();
+    }
+
 };
 
 } // namespace QtPrivate
diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index b4070a27fc..6fe3522f6f 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -377,8 +377,8 @@ public:
     }
 
     void remove(qsizetype i, qsizetype n = 1);
-    void removeFirst() { Q_ASSERT(!isEmpty()); remove(0); }
-    void removeLast() { Q_ASSERT(!isEmpty()); remove(size() - 1); }
+    void removeFirst();
+    void removeLast();
     value_type takeFirst() { Q_ASSERT(!isEmpty()); value_type v = std::move(first()); remove(0); return v; }
     value_type takeLast() { Q_ASSERT(!isEmpty()); value_type v = std::move(last()); remove(size() - 1); return v; }
 
@@ -655,8 +655,26 @@ inline void QList<T>::remove(qsizetype i, qsizetype n)
         // we're detached and we can just move data around
         d->erase(d->begin() + i, d->begin() + i + n);
     }
+
+template <typename T>
+inline void QList<T>::removeFirst()
+{
+    Q_ASSERT(!isEmpty());
+    if (d->needsDetach())
+        d.detach();
+    d->eraseFirst();
 }
 
+template <typename T>
+inline void QList<T>::removeLast()
+{
+    Q_ASSERT(!isEmpty());
+    if (d->needsDetach())
+        detach();
+    d->eraseLast();
+}
+
+
 template<typename T>
 inline T QList<T>::value(qsizetype i, parameter_type defaultValue) const
 {