loplugin:cow_wrapper

check the classes that use o3tl::cow_wrapper so that they
don't unnecessarity trigger copies

Change-Id: I545e627598217f3e61ba2c384adb8d4f8b404829
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122030
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

9 files changed, 186 insertions, 64 deletions

diff --git a/basegfx/source/polygon/b2dpolygon.cxx b/basegfx/source/polygon/b2dpolygon.cxx
index e8f6d947c7d2..7276208cd326 100644
--- a/basegfx/source/polygon/b2dpolygon.cxx
+++ b/basegfx/source/polygon/b2dpolygon.cxx
@@ -1177,9 +1177,9 @@ namespace basegfx
 
     void B2DPolygon::setB2DPoint(sal_uInt32 nIndex, const B2DPoint& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B2DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B2DPolygon access outside range (!)");
 
-        if(mpPolygon->getPoint(nIndex) != rValue)
+        if(std::as_const(*mpPolygon).getPoint(nIndex) != rValue)
         {
             mpPolygon->setPoint(nIndex, rValue);
         }
@@ -1192,7 +1192,7 @@ namespace basegfx
 
     void B2DPolygon::insert(sal_uInt32 nIndex, const B2DPoint& rPoint, sal_uInt32 nCount)
     {
-        OSL_ENSURE(nIndex <= mpPolygon->count(), "B2DPolygon Insert outside range (!)");
+        OSL_ENSURE(nIndex <= std::as_const(*mpPolygon).count(), "B2DPolygon Insert outside range (!)");
 
         if(nCount)
         {
@@ -1204,7 +1204,7 @@ namespace basegfx
     {
         if(nCount)
         {
-            mpPolygon->insert(mpPolygon->count(), rPoint, nCount);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), rPoint, nCount);
         }
     }
 
@@ -1243,10 +1243,10 @@ namespace basegfx
 
     void B2DPolygon::setPrevControlPoint(sal_uInt32 nIndex, const B2DPoint& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B2DPolygon access outside range (!)");
-        const basegfx::B2DVector aNewVector(rValue - mpPolygon->getPoint(nIndex));
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B2DPolygon access outside range (!)");
+        const basegfx::B2DVector aNewVector(rValue - std::as_const(*mpPolygon).getPoint(nIndex));
 
-        if(mpPolygon->getPrevControlVector(nIndex) != aNewVector)
+        if(std::as_const(*mpPolygon).getPrevControlVector(nIndex) != aNewVector)
         {
             mpPolygon->setPrevControlVector(nIndex, aNewVector);
         }
@@ -1254,10 +1254,10 @@ namespace basegfx
 
     void B2DPolygon::setNextControlPoint(sal_uInt32 nIndex, const B2DPoint& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B2DPolygon access outside range (!)");
-        const basegfx::B2DVector aNewVector(rValue - mpPolygon->getPoint(nIndex));
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B2DPolygon access outside range (!)");
+        const basegfx::B2DVector aNewVector(rValue - std::as_const(*mpPolygon).getPoint(nIndex));
 
-        if(mpPolygon->getNextControlVector(nIndex) != aNewVector)
+        if(std::as_const(*mpPolygon).getNextControlVector(nIndex) != aNewVector)
         {
             mpPolygon->setNextControlVector(nIndex, aNewVector);
         }
@@ -1265,12 +1265,12 @@ namespace basegfx
 
     void B2DPolygon::setControlPoints(sal_uInt32 nIndex, const basegfx::B2DPoint& rPrev, const basegfx::B2DPoint& rNext)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B2DPolygon access outside range (!)");
-        const B2DPoint aPoint(mpPolygon->getPoint(nIndex));
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B2DPolygon access outside range (!)");
+        const B2DPoint aPoint(std::as_const(*mpPolygon).getPoint(nIndex));
         const basegfx::B2DVector aNewPrev(rPrev - aPoint);
         const basegfx::B2DVector aNewNext(rNext - aPoint);
 
-        if(mpPolygon->getPrevControlVector(nIndex) != aNewPrev || mpPolygon->getNextControlVector(nIndex) != aNewNext)
+        if(std::as_const(*mpPolygon).getPrevControlVector(nIndex) != aNewPrev || std::as_const(*mpPolygon).getNextControlVector(nIndex) != aNewNext)
         {
             mpPolygon->setControlVectors(nIndex, aNewPrev, aNewNext);
         }
@@ -1278,9 +1278,9 @@ namespace basegfx
 
     void B2DPolygon::resetPrevControlPoint(sal_uInt32 nIndex)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B2DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B2DPolygon access outside range (!)");
 
-        if(mpPolygon->areControlPointsUsed() && !mpPolygon->getPrevControlVector(nIndex).equalZero())
+        if(std::as_const(*mpPolygon).areControlPointsUsed() && !std::as_const(*mpPolygon).getPrevControlVector(nIndex).equalZero())
         {
             mpPolygon->setPrevControlVector(nIndex, B2DVector::getEmptyVector());
         }
@@ -1288,9 +1288,9 @@ namespace basegfx
 
     void B2DPolygon::resetNextControlPoint(sal_uInt32 nIndex)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B2DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B2DPolygon access outside range (!)");
 
-        if(mpPolygon->areControlPointsUsed() && !mpPolygon->getNextControlVector(nIndex).equalZero())
+        if(std::as_const(*mpPolygon).areControlPointsUsed() && !std::as_const(*mpPolygon).getNextControlVector(nIndex).equalZero())
         {
             mpPolygon->setNextControlVector(nIndex, B2DVector::getEmptyVector());
         }
@@ -1298,7 +1298,7 @@ namespace basegfx
 
     void B2DPolygon::resetControlPoints()
     {
-        if(mpPolygon->areControlPointsUsed())
+        if(std::as_const(*mpPolygon).areControlPointsUsed())
         {
             mpPolygon->resetControlVectors();
         }
@@ -1309,12 +1309,12 @@ namespace basegfx
         const B2DPoint& rPrevControlPoint,
         const B2DPoint& rPoint)
     {
-        const B2DVector aNewNextVector(mpPolygon->count() ? B2DVector(rNextControlPoint - mpPolygon->getPoint(mpPolygon->count() - 1)) : B2DVector::getEmptyVector());
+        const B2DVector aNewNextVector(std::as_const(*mpPolygon).count() ? B2DVector(rNextControlPoint - std::as_const(*mpPolygon).getPoint(std::as_const(*mpPolygon).count() - 1)) : B2DVector::getEmptyVector());
         const B2DVector aNewPrevVector(rPrevControlPoint - rPoint);
 
         if(aNewNextVector.equalZero() && aNewPrevVector.equalZero())
         {
-            mpPolygon->insert(mpPolygon->count(), rPoint, 1);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), rPoint, 1);
         }
         else
         {
@@ -1324,7 +1324,7 @@ namespace basegfx
 
     void B2DPolygon::appendQuadraticBezierSegment(const B2DPoint& rControlPoint, const B2DPoint& rPoint)
     {
-        if (mpPolygon->count() == 0)
+        if (std::as_const(*mpPolygon).count() == 0)
         {
             mpPolygon->append(rPoint);
             const double nX((rControlPoint.getX() * 2.0 + rPoint.getX()) / 3.0);
@@ -1333,7 +1333,7 @@ namespace basegfx
         }
         else
         {
-            const B2DPoint aPreviousPoint(mpPolygon->getPoint(mpPolygon->count() - 1));
+            const B2DPoint aPreviousPoint(std::as_const(*mpPolygon).getPoint(std::as_const(*mpPolygon).count() - 1));
 
             const double nX1((rControlPoint.getX() * 2.0 + aPreviousPoint.getX()) / 3.0);
             const double nY1((rControlPoint.getY() * 2.0 + aPreviousPoint.getY()) / 3.0);
@@ -1436,19 +1436,19 @@ namespace basegfx
 
         if(nIndex == 0 && nCount == rPoly.count())
         {
-            mpPolygon->insert(mpPolygon->count(), *rPoly.mpPolygon);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), *rPoly.mpPolygon);
         }
         else
         {
             OSL_ENSURE(nIndex + nCount <= rPoly.mpPolygon->count(), "B2DPolygon Append outside range (!)");
             ImplB2DPolygon aTempPoly(*rPoly.mpPolygon, nIndex, nCount);
-            mpPolygon->insert(mpPolygon->count(), aTempPoly);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), aTempPoly);
         }
     }
 
     void B2DPolygon::remove(sal_uInt32 nIndex, sal_uInt32 nCount)
     {
-        OSL_ENSURE(nIndex + nCount <= mpPolygon->count(), "B2DPolygon Remove outside range (!)");
+        OSL_ENSURE(nIndex + nCount <= std::as_const(*mpPolygon).count(), "B2DPolygon Remove outside range (!)");
 
         if(nCount)
         {
@@ -1498,7 +1498,7 @@ namespace basegfx
 
     void B2DPolygon::transform(const B2DHomMatrix& rMatrix)
     {
-        if(mpPolygon->count() && !rMatrix.isIdentity())
+        if(std::as_const(*mpPolygon).count() && !rMatrix.isIdentity())
         {
             mpPolygon->transform(rMatrix);
         }
diff --git a/basegfx/source/polygon/b2dpolypolygon.cxx b/basegfx/source/polygon/b2dpolypolygon.cxx
index 78b3b7085303..34ff30877ea8 100644
--- a/basegfx/source/polygon/b2dpolypolygon.cxx
+++ b/basegfx/source/polygon/b2dpolypolygon.cxx
@@ -249,7 +249,7 @@ namespace basegfx
 
     void B2DPolyPolygon::setB2DPolygon(sal_uInt32 nIndex, const B2DPolygon& rPolygon)
     {
-        OSL_ENSURE(nIndex < mpPolyPolygon->count(), "B2DPolyPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolyPolygon).count(), "B2DPolyPolygon access outside range (!)");
 
         if(getB2DPolygon(nIndex) != rPolygon)
             mpPolyPolygon->setB2DPolygon(nIndex, rPolygon);
@@ -272,7 +272,7 @@ namespace basegfx
 
     void B2DPolyPolygon::insert(sal_uInt32 nIndex, const B2DPolygon& rPolygon, sal_uInt32 nCount)
     {
-        OSL_ENSURE(nIndex <= mpPolyPolygon->count(), "B2DPolyPolygon Insert outside range (!)");
+        OSL_ENSURE(nIndex <= std::as_const(*mpPolyPolygon).count(), "B2DPolyPolygon Insert outside range (!)");
 
         if(nCount)
             mpPolyPolygon->insert(nIndex, rPolygon, nCount);
@@ -281,7 +281,7 @@ namespace basegfx
     void B2DPolyPolygon::append(const B2DPolygon& rPolygon, sal_uInt32 nCount)
     {
         if(nCount)
-            mpPolyPolygon->insert(mpPolyPolygon->count(), rPolygon, nCount);
+            mpPolyPolygon->insert(std::as_const(*mpPolyPolygon).count(), rPolygon, nCount);
     }
 
     B2DPolyPolygon B2DPolyPolygon::getDefaultAdaptiveSubdivision() const
@@ -310,7 +310,7 @@ namespace basegfx
 
     void B2DPolyPolygon::insert(sal_uInt32 nIndex, const B2DPolyPolygon& rPolyPolygon)
     {
-        OSL_ENSURE(nIndex <= mpPolyPolygon->count(), "B2DPolyPolygon Insert outside range (!)");
+        OSL_ENSURE(nIndex <= std::as_const(*mpPolyPolygon).count(), "B2DPolyPolygon Insert outside range (!)");
 
         if(rPolyPolygon.count())
             mpPolyPolygon->insert(nIndex, rPolyPolygon);
@@ -319,12 +319,12 @@ namespace basegfx
     void B2DPolyPolygon::append(const B2DPolyPolygon& rPolyPolygon)
     {
         if(rPolyPolygon.count())
-            mpPolyPolygon->insert(mpPolyPolygon->count(), rPolyPolygon);
+            mpPolyPolygon->insert(std::as_const(*mpPolyPolygon).count(), rPolyPolygon);
     }
 
     void B2DPolyPolygon::remove(sal_uInt32 nIndex, sal_uInt32 nCount)
     {
-        OSL_ENSURE(nIndex + nCount <= mpPolyPolygon->count(), "B2DPolyPolygon Remove outside range (!)");
+        OSL_ENSURE(nIndex + nCount <= std::as_const(*mpPolyPolygon).count(), "B2DPolyPolygon Remove outside range (!)");
 
         if(nCount)
             mpPolyPolygon->remove(nIndex, nCount);
@@ -360,7 +360,7 @@ namespace basegfx
 
     void B2DPolyPolygon::flip()
     {
-        if(mpPolyPolygon->count())
+        if(std::as_const(*mpPolyPolygon).count())
         {
             mpPolyPolygon->flip();
         }
@@ -389,7 +389,7 @@ namespace basegfx
 
     void B2DPolyPolygon::transform(const B2DHomMatrix& rMatrix)
     {
-        if(mpPolyPolygon->count() && !rMatrix.isIdentity())
+        if(std::as_const(*mpPolyPolygon).count() && !rMatrix.isIdentity())
         {
             mpPolyPolygon->transform(rMatrix);
         }
diff --git a/basegfx/source/polygon/b3dpolygon.cxx b/basegfx/source/polygon/b3dpolygon.cxx
index 364f9f8c0e1d..dac943c79049 100644
--- a/basegfx/source/polygon/b3dpolygon.cxx
+++ b/basegfx/source/polygon/b3dpolygon.cxx
@@ -1431,7 +1431,7 @@ namespace basegfx
 
     void B3DPolygon::setB3DPoint(sal_uInt32 nIndex, const basegfx::B3DPoint& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B3DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B3DPolygon access outside range (!)");
 
         if(getB3DPoint(nIndex) != rValue)
             mpPolygon->setPoint(nIndex, rValue);
@@ -1446,9 +1446,9 @@ namespace basegfx
 
     void B3DPolygon::setBColor(sal_uInt32 nIndex, const BColor& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B3DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B3DPolygon access outside range (!)");
 
-        if(mpPolygon->getBColor(nIndex) != rValue)
+        if(std::as_const(*mpPolygon).getBColor(nIndex) != rValue)
             mpPolygon->setBColor(nIndex, rValue);
     }
 
@@ -1459,7 +1459,7 @@ namespace basegfx
 
     void B3DPolygon::clearBColors()
     {
-        if(mpPolygon->areBColorsUsed())
+        if(std::as_const(*mpPolygon).areBColorsUsed())
             mpPolygon->clearBColors();
     }
 
@@ -1477,15 +1477,15 @@ namespace basegfx
 
     void B3DPolygon::setNormal(sal_uInt32 nIndex, const B3DVector& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B3DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B3DPolygon access outside range (!)");
 
-        if(mpPolygon->getNormal(nIndex) != rValue)
+        if(std::as_const(*mpPolygon).getNormal(nIndex) != rValue)
             mpPolygon->setNormal(nIndex, rValue);
     }
 
     void B3DPolygon::transformNormals(const B3DHomMatrix& rMatrix)
     {
-        if(mpPolygon->areNormalsUsed() && !rMatrix.isIdentity())
+        if(std::as_const(*mpPolygon).areNormalsUsed() && !rMatrix.isIdentity())
             mpPolygon->transformNormals(rMatrix);
     }
 
@@ -1496,7 +1496,7 @@ namespace basegfx
 
     void B3DPolygon::clearNormals()
     {
-        if(mpPolygon->areNormalsUsed())
+        if(std::as_const(*mpPolygon).areNormalsUsed())
             mpPolygon->clearNormals();
     }
 
@@ -1509,15 +1509,15 @@ namespace basegfx
 
     void B3DPolygon::setTextureCoordinate(sal_uInt32 nIndex, const B2DPoint& rValue)
     {
-        OSL_ENSURE(nIndex < mpPolygon->count(), "B3DPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolygon).count(), "B3DPolygon access outside range (!)");
 
-        if(mpPolygon->getTextureCoordinate(nIndex) != rValue)
+        if(std::as_const(*mpPolygon).getTextureCoordinate(nIndex) != rValue)
             mpPolygon->setTextureCoordinate(nIndex, rValue);
     }
 
     void B3DPolygon::transformTextureCoordinates(const B2DHomMatrix& rMatrix)
     {
-        if(mpPolygon->areTextureCoordinatesUsed() && !rMatrix.isIdentity())
+        if(std::as_const(*mpPolygon).areTextureCoordinatesUsed() && !rMatrix.isIdentity())
             mpPolygon->transformTextureCoordinates(rMatrix);
     }
 
@@ -1528,14 +1528,14 @@ namespace basegfx
 
     void B3DPolygon::clearTextureCoordinates()
     {
-        if(mpPolygon->areTextureCoordinatesUsed())
+        if(std::as_const(*mpPolygon).areTextureCoordinatesUsed())
             mpPolygon->clearTextureCoordinates();
     }
 
     void B3DPolygon::append(const basegfx::B3DPoint& rPoint, sal_uInt32 nCount)
     {
         if(nCount)
-            mpPolygon->insert(mpPolygon->count(), rPoint, nCount);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), rPoint, nCount);
     }
 
     void B3DPolygon::append(const B3DPolygon& rPoly, sal_uInt32 nIndex, sal_uInt32 nCount)
@@ -1550,19 +1550,19 @@ namespace basegfx
 
         if(nIndex == 0 && nCount == rPoly.count())
         {
-            mpPolygon->insert(mpPolygon->count(), *rPoly.mpPolygon);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), *rPoly.mpPolygon);
         }
         else
         {
             OSL_ENSURE(nIndex + nCount <= rPoly.mpPolygon->count(), "B3DPolygon Append outside range (!)");
             ImplB3DPolygon aTempPoly(*rPoly.mpPolygon, nIndex, nCount);
-            mpPolygon->insert(mpPolygon->count(), aTempPoly);
+            mpPolygon->insert(std::as_const(*mpPolygon).count(), aTempPoly);
         }
     }
 
     void B3DPolygon::remove(sal_uInt32 nIndex, sal_uInt32 nCount)
     {
-        OSL_ENSURE(nIndex + nCount <= mpPolygon->count(), "B3DPolygon Remove outside range (!)");
+        OSL_ENSURE(nIndex + nCount <= std::as_const(*mpPolygon).count(), "B3DPolygon Remove outside range (!)");
 
         if(nCount)
             mpPolygon->remove(nIndex, nCount);
@@ -1606,7 +1606,7 @@ namespace basegfx
 
     void B3DPolygon::transform(const basegfx::B3DHomMatrix& rMatrix)
     {
-        if(mpPolygon->count() && !rMatrix.isIdentity())
+        if(std::as_const(*mpPolygon).count() && !rMatrix.isIdentity())
         {
             mpPolygon->transform(rMatrix);
         }
diff --git a/basegfx/source/polygon/b3dpolypolygon.cxx b/basegfx/source/polygon/b3dpolypolygon.cxx
index 97ed39c87718..4104d2fc29fe 100644
--- a/basegfx/source/polygon/b3dpolypolygon.cxx
+++ b/basegfx/source/polygon/b3dpolypolygon.cxx
@@ -241,7 +241,7 @@ namespace basegfx
 
     void B3DPolyPolygon::setB3DPolygon(sal_uInt32 nIndex, const B3DPolygon& rPolygon)
     {
-        OSL_ENSURE(nIndex < mpPolyPolygon->count(), "B3DPolyPolygon access outside range (!)");
+        OSL_ENSURE(nIndex < std::as_const(*mpPolyPolygon).count(), "B3DPolyPolygon access outside range (!)");
 
         if(getB3DPolygon(nIndex) != rPolygon)
             mpPolyPolygon->setB3DPolygon(nIndex, rPolygon);
@@ -319,18 +319,18 @@ namespace basegfx
     void B3DPolyPolygon::append(const B3DPolygon& rPolygon, sal_uInt32 nCount)
     {
         if(nCount)
-            mpPolyPolygon->insert(mpPolyPolygon->count(), rPolygon, nCount);
+            mpPolyPolygon->insert(std::as_const(*mpPolyPolygon).count(), rPolygon, nCount);
     }
 
     void B3DPolyPolygon::append(const B3DPolyPolygon& rPolyPolygon)
     {
         if(rPolyPolygon.count())
-            mpPolyPolygon->insert(mpPolyPolygon->count(), rPolyPolygon);
+            mpPolyPolygon->insert(std::as_const(*mpPolyPolygon).count(), rPolyPolygon);
     }
 
     void B3DPolyPolygon::remove(sal_uInt32 nIndex, sal_uInt32 nCount)
     {
-        OSL_ENSURE(nIndex + nCount <= mpPolyPolygon->count(), "B3DPolyPolygon Remove outside range (!)");
+        OSL_ENSURE(nIndex + nCount <= std::as_const(*mpPolyPolygon).count(), "B3DPolyPolygon Remove outside range (!)");
 
         if(nCount)
             mpPolyPolygon->remove(nIndex, nCount);
@@ -369,7 +369,7 @@ namespace basegfx
 
     void B3DPolyPolygon::transform(const B3DHomMatrix& rMatrix)
     {
-        if(mpPolyPolygon->count() && !rMatrix.isIdentity())
+        if(std::as_const(*mpPolyPolygon).count() && !rMatrix.isIdentity())
         {
             mpPolyPolygon->transform(rMatrix);
         }
diff --git a/compilerplugins/clang/cow_wrapper.cxx b/compilerplugins/clang/cow_wrapper.cxx
new file mode 100644
index 000000000000..4c04674f65c1
--- /dev/null
+++ b/compilerplugins/clang/cow_wrapper.cxx
@@ -0,0 +1,88 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * Based on LLVM/Clang.
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ *
+ */
+#ifndef LO_CLANG_SHARED_PLUGINS
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <set>
+#include <unordered_set>
+#include "plugin.hxx"
+#include "check.hxx"
+
+/*
+Look for places where we are using cow_wrapper, but we are calling a const method on the impl object
+with a non-const pointer, which means we will unnnecessarily trigger a copy.
+*/
+
+namespace
+{
+class Cow_Wrapper : public loplugin::FilteringPlugin<Cow_Wrapper>
+{
+public:
+    explicit Cow_Wrapper(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    virtual bool preRun() override { return true; }
+
+    virtual void run() override
+    {
+        if (preRun())
+            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitCXXMemberCallExpr(const CXXMemberCallExpr*);
+};
+
+bool Cow_Wrapper::VisitCXXMemberCallExpr(const CXXMemberCallExpr* memberCallExpr)
+{
+    if (ignoreLocation(memberCallExpr))
+        return true;
+    auto methodDecl = memberCallExpr->getMethodDecl();
+    if (!methodDecl || !methodDecl->isConst())
+        return true;
+
+    auto operatorCallExpr = dyn_cast<CXXOperatorCallExpr>(
+        compat::IgnoreImplicit(memberCallExpr->getImplicitObjectArgument()));
+    if (!operatorCallExpr)
+        return true;
+    if (operatorCallExpr->getOperator() != OO_Arrow)
+        return true;
+    auto arrowMethodDecl = dyn_cast_or_null<CXXMethodDecl>(operatorCallExpr->getDirectCallee());
+    if (!arrowMethodDecl)
+        return true;
+    if (arrowMethodDecl->isConst())
+        return true;
+    auto dc = loplugin::DeclCheck(arrowMethodDecl->getParent())
+                  .Class("cow_wrapper")
+                  .Namespace("o3tl")
+                  .GlobalNamespace();
+    if (!dc)
+        return true;
+
+    report(DiagnosticsEngine::Warning,
+           "calling const method on o3tl::cow_wrapper impl class via non-const pointer, rather use "
+           "std::as_const to prevent triggering an unnecessary copy",
+           compat::getBeginLoc(memberCallExpr))
+        << memberCallExpr->getSourceRange();
+    return true;
+}
+
+loplugin::Plugin::Registration<Cow_Wrapper> cow_wrapper("cow_wrapper", true);
+
+} // namespace
+
+#endif // LO_CLANG_SHARED_PLUGINS
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/compilerplugins/clang/test/cow_wrapper.cxx b/compilerplugins/clang/test/cow_wrapper.cxx
new file mode 100644
index 000000000000..705a4052ef66
--- /dev/null
+++ b/compilerplugins/clang/test/cow_wrapper.cxx
@@ -0,0 +1,33 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include "config_clang.h"
+#include "o3tl/cow_wrapper.hxx"
+
+struct ImplBitmapPalette
+{
+    void foo() const;
+};
+
+struct BitmapPalette
+{
+    void foo1()
+    {
+        // expected-error@+1 {{calling const method on o3tl::cow_wrapper impl class via non-const pointer, rather use std::as_const to prevent triggering an unnecessary copy [loplugin:cow_wrapper]}}
+        mpImpl->foo();
+    }
+    void foo2() const
+    {
+        // no error expected
+        mpImpl->foo();
+    }
+    o3tl::cow_wrapper<ImplBitmapPalette> mpImpl;
+};
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/solenv/CompilerTest_compilerplugins_clang.mk b/solenv/CompilerTest_compilerplugins_clang.mk
index 768b5a579d04..0bbfcefe9db1 100644
--- a/solenv/CompilerTest_compilerplugins_clang.mk
+++ b/solenv/CompilerTest_compilerplugins_clang.mk
@@ -25,6 +25,7 @@ $(eval $(call gb_CompilerTest_add_exception_objects,compilerplugins_clang, \
     compilerplugins/clang/test/consttobool \
     compilerplugins/clang/test/constvars \
     compilerplugins/clang/test/convertlong \
+    compilerplugins/clang/test/cow_wrapper \
     compilerplugins/clang/test/cppunitassertequals \
     compilerplugins/clang/test/cstylecast \
     compilerplugins/clang/test/datamembershadow \
diff --git a/svx/source/xoutdev/_xpoly.cxx b/svx/source/xoutdev/_xpoly.cxx
index f3bb16a1419f..c4d74b996735 100644
--- a/svx/source/xoutdev/_xpoly.cxx
+++ b/svx/source/xoutdev/_xpoly.cxx
@@ -322,7 +322,7 @@ XPolygon::~XPolygon() = default;
 
 void XPolygon::SetPointCount( sal_uInt16 nPoints )
 {
-    pImpXPolygon->CheckPointDelete();
+    std::as_const(*pImpXPolygon).CheckPointDelete();
 
     if( pImpXPolygon->nSize < nPoints )
         pImpXPolygon->Resize( nPoints );
@@ -425,7 +425,7 @@ const Point& XPolygon::operator[]( sal_uInt16 nPos ) const
 
 Point& XPolygon::operator[]( sal_uInt16 nPos )
 {
-    pImpXPolygon->CheckPointDelete();
+    std::as_const(*pImpXPolygon).CheckPointDelete();
 
     if( nPos >= pImpXPolygon->nSize )
     {
@@ -458,7 +458,7 @@ PolyFlags XPolygon::GetFlags( sal_uInt16 nPos ) const
 /// set the flags for the point at the given position
 void XPolygon::SetFlags( sal_uInt16 nPos, PolyFlags eFlags )
 {
-    pImpXPolygon->CheckPointDelete();
+    std::as_const(*pImpXPolygon).CheckPointDelete();
     pImpXPolygon->pFlagAry[nPos] = eFlags;
 }
 
@@ -741,7 +741,7 @@ void XPolygon::PointsToBezier(sal_uInt16 nFirst)
 /// scale in X- and/or Y-direction
 void XPolygon::Scale(double fSx, double fSy)
 {
-    pImpXPolygon->CheckPointDelete();
+    std::as_const(*pImpXPolygon).CheckPointDelete();
 
     sal_uInt16 nPntCnt = pImpXPolygon->nPoints;
 
@@ -766,7 +766,7 @@ void XPolygon::Scale(double fSx, double fSy)
 void XPolygon::Distort(const tools::Rectangle& rRefRect,
                        const XPolygon& rDistortedRect)
 {
-    pImpXPolygon->CheckPointDelete();
+    std::as_const(*pImpXPolygon).CheckPointDelete();
 
     tools::Long    Xr, Wr;
     tools::Long    Yr, Hr;
diff --git a/vcl/source/font/font.cxx b/vcl/source/font/font.cxx
index 275eb5fe97a2..1681159b015a 100644
--- a/vcl/source/font/font.cxx
+++ b/vcl/source/font/font.cxx
@@ -164,7 +164,7 @@ void Font::SetSymbolFlag( bool bSymbol )
     }
     else
     {
-        if ( mpImplFont->GetCharSet() == RTL_TEXTENCODING_SYMBOL )
+        if ( std::as_const(*mpImplFont).GetCharSet() == RTL_TEXTENCODING_SYMBOL )
             mpImplFont->SetCharSet( RTL_TEXTENCODING_DONTKNOW );
     }
 }
@@ -830,9 +830,9 @@ const OUString& Font::GetFamilyName() const { return mpImplFont->GetFamilyName()
 const OUString& Font::GetStyleName() const { return mpImplFont->maStyleName; }
 
 const Size& Font::GetFontSize() const { return mpImplFont->GetFontSize(); }
-void Font::SetFontHeight( tools::Long nHeight ) { SetFontSize( Size( mpImplFont->GetFontSize().Width(), nHeight ) ); }
+void Font::SetFontHeight( tools::Long nHeight ) { SetFontSize( Size( std::as_const(*mpImplFont).GetFontSize().Width(), nHeight ) ); }
 tools::Long Font::GetFontHeight() const { return mpImplFont->GetFontSize().Height(); }
-void Font::SetAverageFontWidth( tools::Long nWidth ) { SetFontSize( Size( nWidth, mpImplFont->GetFontSize().Height() ) ); }
+void Font::SetAverageFontWidth( tools::Long nWidth ) { SetFontSize( Size( nWidth, std::as_const(*mpImplFont).GetFontSize().Height() ) ); }
 tools::Long Font::GetAverageFontWidth() const { return mpImplFont->GetFontSize().Width(); }
 
 rtl_TextEncoding Font::GetCharSet() const { return mpImplFont->GetCharSet(); }