[dxvk] Only update buffer object in buffer slices if necessary

Saves CPU cycles when rebinding the same vertex, index and
constant buffers with different offsets.

src/dxvk/dxvk_buffer.h

@@ -333,6 +333,23 @@ namespace dxvk {
     explicit DxvkBufferSlice(const Rc<DxvkBuffer>& buffer)
     : DxvkBufferSlice(buffer, 0, buffer->info().size) { }
 
+    DxvkBufferSlice(const DxvkBufferSlice& ) = default;
+    DxvkBufferSlice(      DxvkBufferSlice&&) = default;
+
+    DxvkBufferSlice& operator = (const DxvkBufferSlice& other) {
+      if (m_buffer != other.m_buffer)
+        m_buffer = other.m_buffer;
+      m_offset = other.m_offset;
+      m_length = other.m_length;
+      return *this;
+    }
+
+    DxvkBufferSlice& operator = (DxvkBufferSlice&&) = default;
+
+    /**
+     * \brief Buffer slice offset and length
+     * \returns Buffer slice offset and length
+     */
     size_t offset() const { return m_offset; }
     size_t length() const { return m_length; }
 
@@ -475,19 +492,6 @@ namespace dxvk {
           && this->m_length == other.m_length;
     }
     
-    /**
-     * \brief Changes offset and size, but not the buffer
-     *
-     * Slightly faster alternative to overriding the full
-     * buffer slice object in case only the range changes.
-     * \param [in] offset New slice offset
-     * \param [in] length New slice length
-     */
-    void updateRange(VkDeviceSize offset, VkDeviceSize length) {
-      m_offset = offset;
-      m_length = length;
-    }
-    
   private:
     
     Rc<DxvkBuffer> m_buffer = nullptr;

src/dxvk/dxvk_context.cpp

@@ -165,9 +165,7 @@ namespace dxvk {
         DxvkContextFlag::CpDirtyResources,
         DxvkContextFlag::GpDirtyResources);
     } else if (!m_rc[slot].bufferSlice.matchesRange(buffer)) {
-      m_rc[slot].bufferSlice.updateRange(
+      m_rc[slot].bufferSlice = buffer;
-        buffer.offset(),
-        buffer.length());
       
       m_flags.set(
         DxvkContextFlag::CpDirtyDescriptorOffsets,