Fixed issue in filter leading to sanitizer errors.

vtkDataSetSurfaceFilter had some funky code designed to optimize
(minimize) allocation of small objects. This required apparently
writing beyond the limits of an array. It was not a bug but made
tools like the clang sanitizer think that it was. Fixed it while
still maintaining the allocation optimization, at the cost of a
bit more memory usage.

Change-Id: I3ef7051e85601a4440f02cb4dfe2e15227a06e87

Filters/Geometry/vtkDataSetSurfaceFilter.cxx

@@ -52,8 +52,18 @@
 
 static inline int sizeofFastQuad(int numPts)
 {
-  // account for size of ptArray
-  return static_cast<int>(sizeof(vtkFastGeomQuad)+(numPts-4)*sizeof(vtkIdType));
+  const int qsize = sizeof(vtkFastGeomQuad);
+  const int sizeId = sizeof(vtkIdType);
+  // If necessary, we create padding after vtkFastGeomQuad such that
+  // the beginning of ids aligns evenly with sizeof(vtkIdType).
+  if (qsize % sizeId == 0)
+    {
+    return static_cast<int>(qsize+numPts*sizeId);
+    }
+  else
+    {
+    return static_cast<int>((qsize/sizeId+1+numPts)*sizeId);
+    }
 }
 
 class vtkDataSetSurfaceFilter::vtkEdgeInterpolationMap
@@ -2315,6 +2325,19 @@ vtkFastGeomQuad* vtkDataSetSurfaceFilter::NewFastGeomQuad(int numPts)
     (this->FastGeomQuadArrays[this->NextArrayIndex] + this->NextQuadIndex);
   q->numPts = numPts;
 
+  const int qsize = sizeof(vtkFastGeomQuad);
+  const int sizeId = sizeof(vtkIdType);
+  // If necessary, we create padding after vtkFastGeomQuad such that
+  // the beginning of ids aligns evenly with sizeof(vtkIdType).
+  if (qsize % sizeId == 0)
+    {
+    q->ptArray = (vtkIdType*)q + qsize/sizeId;
+    }
+  else
+    {
+    q->ptArray = (vtkIdType*)q + qsize/sizeId + 1;
+    }
+
   this->NextQuadIndex += polySize;
 
   return q;

Filters/Geometry/vtkDataSetSurfaceFilter.h

@@ -40,7 +40,7 @@ struct vtkFastGeomQuadStruct
   struct vtkFastGeomQuadStruct *Next;
   vtkIdType SourceId;
   int numPts;
-  vtkIdType ptArray[4]; // actually a variable length array.  MUST be last
+  vtkIdType* ptArray;
 };
 typedef struct vtkFastGeomQuadStruct vtkFastGeomQuad;
 //ETX