add option to initialize heap with a known number of elements, since this may be known in advance - it avoids re-allocing too much.

source/blender/blenlib/BLI_heap.h

@@ -42,6 +42,7 @@ typedef void (*HeapFreeFP)(void *ptr);
 
 /* Creates a new heap. BLI_memarena is used for allocating nodes. Removed nodes
  * are recycled, so memory usage will not shrink. */
+Heap           *BLI_heap_new_ex(unsigned int tot_reserve);
 Heap           *BLI_heap_new(void);
 void            BLI_heap_free(Heap *heap, HeapFreeFP ptrfreefp);
 

source/blender/blenlib/intern/BLI_heap.c

@@ -67,16 +67,22 @@ struct Heap {
 
 /***/
 
-Heap *BLI_heap_new(void)
+/* use when the size of the heap is known in advance */
+Heap *BLI_heap_new_ex(unsigned int tot_reserve)
 {
 	Heap *heap = (Heap *)MEM_callocN(sizeof(Heap), __func__);
-	heap->bufsize = 1;
-	heap->tree = (HeapNode **)MEM_mallocN(sizeof(HeapNode *), "BLIHeapTree");
+	heap->bufsize = tot_reserve;
+	heap->tree = (HeapNode **)MEM_mallocN(tot_reserve * sizeof(HeapNode *), "BLIHeapTree");
 	heap->arena = BLI_memarena_new(1 << 16, "heap arena");
 
 	return heap;
 }
 
+Heap *BLI_heap_new(void)
+{
+	return BLI_heap_new_ex(1);
+}
+
 void BLI_heap_free(Heap *heap, HeapFreeFP ptrfreefp)
 {
 	int i;

source/blender/bmesh/intern/bmesh_decimate.c

@@ -531,7 +531,7 @@ void BM_mesh_decimate(BMesh *bm, const float factor)
 
 	/* alloc vars */
 	vquadrics = MEM_callocN(sizeof(Quadric) * bm->totvert, __func__);
-	eheap = BLI_heap_new();
+	eheap = BLI_heap_new_ex(bm->totedge);
 	eheap_table = MEM_callocN(sizeof(HeapNode *) * bm->totedge, __func__);
 	tot_edge_orig = bm->totedge;
 

source/blender/modifiers/intern/MOD_decimate.c

@@ -47,6 +47,10 @@
 #include "BKE_particle.h"
 #include "BKE_cdderivedmesh.h"
 
+#include "BKE_tessmesh.h"
+
+/* testing only! - Campbell */
+// #define USE_DECIMATE_BMESH
 
 #ifdef WITH_MOD_DECIMATE
 #include "LOD_decimation.h"
@@ -70,6 +74,33 @@ static void copyData(ModifierData *md, ModifierData *target)
 }
 
 #ifdef WITH_MOD_DECIMATE
+#ifdef USE_DECIMATE_BMESH
+
+#include "bmesh.h"
+
+static DerivedMesh *applyModifier(ModifierData *md, Object *UNUSED(ob),
+                                  DerivedMesh *derivedData,
+                                  ModifierApplyFlag UNUSED(flag))
+{
+	DecimateModifierData *dmd = (DecimateModifierData *) md;
+	DerivedMesh *dm = derivedData, *result = NULL;
+	BMEditMesh *em;
+	BMesh *bm;
+
+	em = DM_to_editbmesh(dm, NULL, FALSE);
+	bm = em->bm;
+
+	BM_mesh_decimate(bm, dmd->percent);
+
+	BLI_assert(em->looptris == NULL);
+	result = CDDM_from_BMEditMesh(em, NULL, TRUE, FALSE);
+	BMEdit_Free(em);
+	MEM_freeN(em);
+
+	return result;
+}
+
+#else
 static DerivedMesh *applyModifier(ModifierData *md, Object *UNUSED(ob),
                                   DerivedMesh *derivedData,
                                   ModifierApplyFlag UNUSED(flag))
@@ -192,6 +223,7 @@ static DerivedMesh *applyModifier(ModifierData *md, Object *UNUSED(ob),
 		return dm;
 	}
 }
+#endif // USE_DECIMATE_BMESH
 #else // WITH_MOD_DECIMATE
 static DerivedMesh *applyModifier(ModifierData *UNUSED(md), Object *UNUSED(ob),
                                   DerivedMesh *derivedData,