Copy mail merge source instead of loading

Currently a mail merge loads the styles from the source document
and also loads the original source per mail merge dataset.

The new code is based on the MergeDocuments function and swaps the
loading with an internal document copy to improve mail merge
throughtput.

For a mail merge with 99 datasets and a two pages document,
callgrind shows an improvement from routhly 44 to 31 billion
inclusive instructions for the single SwXMailMerge::execute call.

Change-Id: I6929ba371f81c3ea1f26ea3a25e7751bc53256e3
Reviewed-on: https://gerrit.libreoffice.org/7433Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

sw/source/ui/dbui/dbmgr.cxx

@@ -869,11 +869,8 @@ sal_Bool SwNewDBMgr::MergeMailFiles(SwWrtShell* pSourceShell,
         pSfxDispatcher->Execute( pSourceDocSh->HasName() ? SID_SAVEDOC : SID_SAVEASDOC, SFX_CALLMODE_SYNCHRON|SFX_CALLMODE_RECORD);
         if( !pSourceDocSh->IsModified() )
         {
-            SfxMedium* pOrig = pSourceDocSh->GetMedium();
-            OUString sSourceDocumentURL(pOrig->GetURLObject().GetMainURL( INetURLObject::NO_DECODE ));
-            const SfxFilter* pSfxFlt = SwIoSystem::GetFileFilter(
-                                                    sSourceDocumentURL, ::aEmptyOUStr );
-            const SfxFilter* pStoreToFilter = pSfxFlt;
+            const SfxFilter* pStoreToFilter = SwIoSystem::GetFileFilter(
+                pSourceDocSh->GetMedium()->GetURLObject().GetMainURL( INetURLObject::NO_DECODE ), ::aEmptyOUStr );
             SfxFilterContainer* pFilterContainer = SwDocShell::Factory().GetFilterContainer();
             const OUString* pStoreToFilterOptions = 0;
 
@@ -922,14 +919,7 @@ sal_Bool SwNewDBMgr::MergeMailFiles(SwWrtShell* pSourceShell,
                 pTargetView->AttrChangedNotify( &pTargetView->GetWrtShell() );
                 pTargetShell = pTargetView->GetWrtShellPtr();
                 //copy the styles from the source to the target document
-                SwgReaderOption aOpt;
-                aOpt.SetTxtFmts( sal_True );
-                aOpt.SetFrmFmts( sal_True );
-                aOpt.SetPageDescs( sal_True );
-                aOpt.SetNumRules( sal_True );
-                aOpt.SetMerge( sal_False );
-                pTargetView->GetDocShell()->LoadStylesFromFile(
-                        sSourceDocumentURL, aOpt, sal_True );
+                pTargetView->GetDocShell()->_LoadStyles( *pSourceDocSh, sal_True );
                 //determine the page style and number used at the start of the source document
                 pSourceShell->SttEndDoc(sal_True);
                 nStartingPageNo = pSourceShell->GetVirtPageNum();
@@ -1026,13 +1016,19 @@ sal_Bool SwNewDBMgr::MergeMailFiles(SwWrtShell* pSourceShell,
                         for (sal_uInt16 i = 0; i < 25; i++)
                             Application::Reschedule();
 
-                        // Create and save new document
                         // The SfxObjectShell will be closed explicitly later but it is more safe to use SfxObjectShellLock here
-                        SfxObjectShellLock xWorkDocSh( new SwDocShell( SFX_CREATE_MODE_INTERNAL ));
-                        SfxMedium* pWorkMed = new SfxMedium( sSourceDocumentURL, STREAM_STD_READ );
-                        pWorkMed->SetFilter( pSfxFlt );
+                        SfxObjectShellLock xWorkDocSh;
+                        // copy the source document
+                        if( 1 == nDocNo && (bAsSingleFile || rMergeDescriptor.bCreateSingleFile) )
+                        {
+                            uno::Reference< util::XCloneable > xClone( pSourceDocSh->GetModel(), uno::UNO_QUERY);
+                            uno::Reference< lang::XUnoTunnel > xWorkDocShell( xClone->createClone(), uno::UNO_QUERY);
+                            SwXTextDocument* pWorkModel = reinterpret_cast<SwXTextDocument*>(xWorkDocShell->getSomething(SwXTextDocument::getUnoTunnelId()));
+                            xWorkDocSh = pWorkModel->GetDocShell();
+                        }
+                        else
+                            xWorkDocSh = pSourceDocSh->GetDoc()->CreateCopy( true );
 
-                        if (xWorkDocSh->DoLoad(pWorkMed))
                         {
                             //create a view frame for the document
                             SfxViewFrame* pWorkFrame = SfxViewFrame::LoadHiddenDocument( *xWorkDocSh, 0 );