According to a post from Robert Duffy, CTO at id Software, the new patch will allow some older GPUs to run the game with playable framerates and the developer has been working with both AMD and Nvidia to provide such support.
And according to a post over at Radeon.com, made by Sasa Marinkovic, Head of VR and Software Marketing at AMD, the new Vulkan API, is a descendant of AMD's Mantle, supports "close-to-metal" control and reduces API overhead, which should bring significant performance improvements. Its implementation in Doom benefits from several features, including Asynchronous Shaders, Shaders Intrinsics, also known as Shader Intrinsic Functions, as well as the Frame Flip Optimizations.
As you may know, the Asynchronous Compute Engines in AMD's GCN and Polaris architecture can submit commands without waiting for other tasks to complete and should bring significant performance improvements. The Shader Intrinsics or Shader Intrinsic Functions, let developers directly access graphics hardware instructions in certain situations while Frame Flip Optimizations pass the frame directly to the display once it is ready, skipping the copy and save process.
According to AMD's internal testing, the performance of Doom on RX 480 and Vulkan API is significantly increased compared to the OpenGL, by up to 27 percent at 1920x1080 and up to 23 at 2560x1440 resolutions.
Earlier, Bethesda released the "Update 1" which brought a number of game fixes and features while the new patch should provide significant performance improvements. Of course, the patch should be combined with latest AMD and Nvidia drivers.
We haven't had a chance to try it out but we might include some results in our upcoming graphics card reviews.