ODS load perf: accelerate CompileXML for formula by stringify and compare.

For long columns of repeated formula, it is far faster to convert a formula
to a string and compare to see if the next cell in a column matches, than
it is to parse the formula string itself (sad but true).

This saves 29s of 131s of load time for my (admittedly large) ODS file.

Re-instate commit - with pCode now correctly intialized.

Change-Id: Ib25840e7916c3e1c681c8100678770b7ab7222ab

sc/source/core/data/formulacell.cxx

@@ -1184,9 +1184,50 @@ void ScFormulaCell::CompileXML( sc::CompileFormulaContext& rCxt, ScProgress& rPr
     // pCode may not deleted for queries, but must be empty
     if ( pCode )
         pCode->Clear();
-    ScTokenArray* pCodeOld = pCode;
-    pCode = aComp.CompileString( aFormula, aFormulaNmsp );
-    delete pCodeOld;
+
+    bool bSkipCompile = false;
+
+    if ( !mxGroup && aFormulaNmsp.isEmpty() ) // optimization
+    {
+        ScAddress aPreviousCell( aPos );
+        aPreviousCell.IncRow( -1 );
+        ScFormulaCell *pPreviousCell = pDocument->GetFormulaCell( aPreviousCell );
+        if( pPreviousCell )
+        {
+            // Now try to convert to a string quickly ...
+            ScCompiler aBackComp( rCxt, aPos, *(pPreviousCell->pCode) );
+            OUStringBuffer aShouldBeBuf;
+            aBackComp.CreateStringFromTokenArray( aShouldBeBuf );
+
+            assert( aFormula[0] == '=' );
+            OUString aShouldBe = aShouldBeBuf.makeStringAndClear();
+            if( aFormula.getLength() == aShouldBe.getLength() + 1 &&
+                aFormula.match( aShouldBe, 1 ) ) // initial '='
+            {
+                // Put them in the same formula group.
+                ScFormulaCellGroupRef xGroup = pPreviousCell->GetCellGroup();
+                if (!xGroup) // Last cell is not grouped yet. Start a new group.
+                    xGroup = pPreviousCell->CreateCellGroup(1, false);
+                ++xGroup->mnLength;
+                SetCellGroup( xGroup );
+
+                bSkipCompile = true;
+                pCode = pPreviousCell->pCode;
+
+                SAL_INFO( "sc", "merged '" << aFormula << "' == "
+                          "'" << aShouldBe << "'" <<
+                          " extend group to " << xGroup->mnLength );
+            }
+        }
+    }
+
+    if (!bSkipCompile)
+    {
+        ScTokenArray* pCodeOld = pCode;
+        pCode = aComp.CompileString( aFormula, aFormulaNmsp );
+        delete pCodeOld;
+    }
+
     if( !pCode->GetCodeError() )
     {
         if ( !pCode->GetLen() )