patch and measured numbers

crossTileSymbolIndex.pruneUnusedLayers.patch

diff --git a/src/mbgl/renderer/renderer_impl.cpp b/src/mbgl/renderer/renderer_impl.cpp
index 76c45aef7..a45c14d45 100644
--- a/src/mbgl/renderer/renderer_impl.cpp
+++ b/src/mbgl/renderer/renderer_impl.cpp
@@ -31,6 +31,8 @@
 #include <mbgl/util/string.hpp>
 #include <mbgl/util/logging.hpp>
 
+#import <QuartzCore/QuartzCore.h>
+
 namespace mbgl {
 
 using namespace style;
@@ -332,9 +334,14 @@ void Renderer::Impl::render(const UpdateParameters& updateParameters) {
         }
 
         if (placementChanged) {
+            auto t0 = CACurrentMediaTime();
             placement->commit(updateParameters.timePoint);
+            auto t1 = CACurrentMediaTime();
             crossTileSymbolIndex.pruneUnusedLayers(usedSymbolLayers);
+            auto t2 = CACurrentMediaTime();
             updateFadingTiles();
+            auto t3 = (CACurrentMediaTime() - t2) * 1000;
+            printf("placementChanged %f \t %f \t %f ms\n", (t1 - t0) * 1000, (t2 - t1) * 1000, t3);
         } else {
             placement->setStale();
         }


placementChanged 0.938917 	 1.945875 	 0.004750 ms
placementChanged 0.849042 	 1.825333 	 0.005917 ms
placementChanged 1.054750 	 1.780125 	 0.005125 ms
placementChanged 1.028125 	 2.045833 	 0.007958 ms
placementChanged 1.084875 	 1.912250 	 0.004958 ms
placementChanged 0.900542 	 1.993000 	 0.005375 ms
placementChanged 0.967333 	 1.952333 	 0.007500 ms