Currently, when using shaders compiled with rust-gpu on older Vulkan versions, we get validation errors like in #163. That is fixable for the example in theory by upgrading the Vulkan version to latest, for which there's tracking issues in gfx-rs: gfx-rs/gfx#3146 and gfx-rs/gfx#3302

However, this is probably also a design decision in terms of what exactly the limitations are for older versions of SPIR-V (for example I think a big one is subgroup operations which are only found in Vulkan 1.1/SPIR-V 1.3+) and whether we want to support them or not.