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

cc/playback/raster_source.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #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"
 #include "cc/debug/debug_colors.h"
 #include "cc/playback/display_item_list.h"
 #include "cc/playback/image_hijack_canvas.h"
 #include "cc/playback/skip_image_canvas.h"
 #include "skia/ext/analysis_canvas.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkClipStack.h"
@@ skipping 48 matching lines @@
 
 void RasterSource::PlaybackToCanvas(SkCanvas* raster_canvas,
                                     const gfx::Rect& canvas_bitmap_rect,
                                     const gfx::Rect& canvas_playback_rect,
                                     float contents_scale,
                                     const PlaybackSettings& settings) const {
   SkIRect raster_bounds = gfx::RectToSkIRect(canvas_bitmap_rect);
   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());
   raster_canvas->clipRect(SkRect::MakeFromIRect(raster_bounds));
   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,
                                     const PlaybackSettings& settings) const {
   if (!settings.playback_to_shared_canvas)
     PrepareForPlaybackToCanvas(raster_canvas);
 
   if (settings.skip_images) {
     SkipImageCanvas canvas(raster_canvas);
     RasterCommon(&canvas, nullptr);
@@ skipping 202 matching lines @@
   bool can_use_lcd_text = false;
   return scoped_refptr<RasterSource>(new RasterSource(this, can_use_lcd_text));
 }
 
 RasterSource::PlaybackSettings::PlaybackSettings()
     : playback_to_shared_canvas(false),
       skip_images(false),
       use_image_hijack_canvas(true) {}
 
 }  // namespace cc