Always add a barrier when old layout was general in vulkan.

src/gpu/vk/GrVkImage.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrVkGpu.h"
 #include "GrVkImage.h"
 #include "GrVkMemory.h"
@@ skipping 14 matching lines @@
     }
 }
 
 void GrVkImage::setImageLayout(const GrVkGpu* gpu, VkImageLayout newLayout,
                                VkAccessFlags dstAccessMask,
                                VkPipelineStageFlags dstStageMask,
                                bool byRegion) {
     SkASSERT(VK_IMAGE_LAYOUT_UNDEFINED != newLayout &&
              VK_IMAGE_LAYOUT_PREINITIALIZED != newLayout);
     VkImageLayout currentLayout = this->currentLayout();
-    // Is this reasonable? Could someone want to keep the same layout but use the masks to force
-    // a barrier on certain things?
-    if (newLayout == currentLayout) {
+
+    // If the old and new layout are the same, there is no reason to put in a barrier since the
+    // operations used for each layout are implicitly synchronized with eachother. The one exception
+    // is if the layout is GENERAL. In this case the image could have been used for any operation so
+    // we must respect the barrier.
+    if (newLayout == currentLayout && VK_IMAGE_LAYOUT_GENERAL != currentLayout) {
         return;
     }
 
     VkAccessFlags srcAccessMask = GrVkMemory::LayoutToSrcAccessMask(currentLayout);
     VkPipelineStageFlags srcStageMask = GrVkMemory::LayoutToPipelineStageFlags(currentLayout);
 
     VkImageAspectFlags aspectFlags = vk_format_to_aspect_flags(fInfo.fFormat);
     VkImageMemoryBarrier imageMemoryBarrier = {
         VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER,          // sType
         nullptr,                                         // pNext
@@ skipping 101 matching lines @@
 }
 
 void GrVkImage::Resource::freeGPUData(const GrVkGpu* gpu) const {
     VK_CALL(gpu, DestroyImage(gpu->device(), fImage, nullptr));
     bool isLinear = (VK_IMAGE_TILING_LINEAR == fImageTiling);
     GrVkMemory::FreeImageMemory(gpu, isLinear, fAlloc);
 }
 
 void GrVkImage::BorrowedResource::freeGPUData(const GrVkGpu* gpu) const {
 }