cc: disable denorm handling before calling into Skia's filter code.

cc/playback/raster_source.cc

Index: cc/playback/raster_source.cc
diff --git a/cc/playback/raster_source.cc b/cc/playback/raster_source.cc
index f38f9dd08ff7c8dcdd74f8f239360860c9879aa0..c2fd7fcf9f8444a44f960d4feff5e3be9284edeb 100644
--- a/cc/playback/raster_source.cc
+++ b/cc/playback/raster_source.cc
@@ -5,6 +5,9 @@
 #include "cc/playback/raster_source.h"
 
 #include <stddef.h>
+#ifdef __SSE__
+#include <xmmintrin.h>
+#endif
 
 #include "base/trace_event/trace_event.h"
 #include "cc/base/region.h"
@@ -73,6 +76,12 @@ void RasterSource::PlaybackToCanvas(SkCanvas* raster_canvas,
   if (!canvas_playback_rect.IsEmpty() &&
       !raster_bounds.intersect(gfx::RectToSkIRect(canvas_playback_rect)))
     return;
+#ifdef __SSE__
+  // Turn on "subnormals are zero" and "flush to zero" CSR flags for
+  // performance.
+  unsigned int csr = _mm_getcsr();
+  _mm_setcsr(csr | 0x8040);
+#endif

[piman, 2016/07/25 20:28:40]

This may be needed in more places - e.g. software renderer. Also, we may end up
needing an ARM version. Do you think it could make sense to make a
ScopedFlushSubnormalsToZero in some header (forces flush-to-zero in constructor,
restore in destructor), and use it here?

 
   raster_canvas->save();
   raster_canvas->translate(-canvas_bitmap_rect.x(), -canvas_bitmap_rect.y());
@@ -80,6 +89,9 @@ void RasterSource::PlaybackToCanvas(SkCanvas* raster_canvas,
   raster_canvas->scale(contents_scale, contents_scale);
   PlaybackToCanvas(raster_canvas, settings);
   raster_canvas->restore();
+#ifdef __SSE__
+  _mm_setcsr(csr);
+#endif
 }
 
 void RasterSource::PlaybackToCanvas(SkCanvas* raster_canvas,