Vulkan: Optimize element buffer conversion

src/libANGLE/renderer/vulkan/ContextVk.cpp

@@ -958,8 +958,24 @@ angle::Result ContextVk::setupIndexedDraw(const gl::Context *context,
         if (indexType == gl::DrawElementsType::UnsignedByte &&
             mGraphicsDirtyBits[DIRTY_BIT_INDEX_BUFFER])
         {
-            BufferVk *bufferVk = vk::GetImpl(elementArrayBuffer);
-            ANGLE_TRY(mVertexArray->convertIndexBufferGPU(this, bufferVk, indices));
+            BufferVk *bufferVk             = vk::GetImpl(elementArrayBuffer);
+            vk::BufferHelper &bufferHelper = bufferVk->getBuffer();
+
+            if (bufferHelper.isHostVisible() &&
+                !bufferHelper.isCurrentlyInUse(getLastCompletedQueueSerial()))
+            {
+                uint8_t *src = nullptr;
+                ANGLE_TRY(bufferVk->mapImpl(this, reinterpret_cast<void **>(&src)));
+                src += reinterpret_cast<uintptr_t>(indices);
+                const size_t byteCount = static_cast<size_t>(elementArrayBuffer->getSize()) -
+                                         reinterpret_cast<uintptr_t>(indices);
+                ANGLE_TRY(mVertexArray->convertIndexBufferCPU(this, indexType, byteCount, src));
+                bufferVk->unmapImpl(this);
+            }
+            else
+            {
+                ANGLE_TRY(mVertexArray->convertIndexBufferGPU(this, bufferVk, indices));
+            }
         }
     }
 

src/libANGLE/renderer/vulkan/vk_helpers.h

@@ -475,6 +475,10 @@ class BufferHelper final : public Resource
     const Buffer &getBuffer() const { return mBuffer; }
     const DeviceMemory &getDeviceMemory() const { return mDeviceMemory; }
     VkDeviceSize getSize() const { return mSize; }
+    bool isHostVisible() const
+    {
+        return (mMemoryPropertyFlags & VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT) != 0;
+    }
 
     // Set write access mask when the buffer is modified externally, e.g. by host.  There is no
     // graph resource to create a dependency to.