I believe this may help getting things working on Android.

On an internal issue, @VZout said:

My minimal test case right now is just 2 entry points with vertex index to reproduce the pipeline creation failure

Here's my theory. If you have two shaders set up like this:

#[spirv(vertex)]
pub fn vs_1(#[spirv(vertex_index)] vert_id: Input<i32>) { }
#[spirv(vertex)]
pub fn vs_2(#[spirv(vertex_index)] vert_id: Input<i32>) { }

then right now, rust-gpu will generate two OpVariables: one per entry point. Each OpVariable will get used in their respective vertex shader, and all is well and good... until we arrive at buggy android shader compilers. My guess is that it emits some automatic intrinsic code, or something, idk, when it encounters a vertex index OpVariable. Then, it hits another vertex index OpVariable, and says "wait we already did that, oops, crash", even though they're only used in separate shaders, never at the same time.

My theory is that emitting a single OpVariable for both shaders will make it happy. But, I don't have @VZout's testing code, so I'm putting this up and seeing if it works~

However! An open question is what to deduplicate on. If the descriptor set, binding, location, type, or any other decoration differs, then obviously we shouldn't deduplicate it. But... what if it has a different OpName? For some use cases, we should keep both around! They're different names, different things, shows up differently in OpenGL when searching for uniforms by name! But for some use cases, we should deduplicate them - for example, the following would generate two vertex index OpVariables, which isn't great!

#[spirv(vertex)]
pub fn vs_1(#[spirv(vertex_index)] one: Input<i32>) { }
#[spirv(vertex)]
pub fn vs_2(#[spirv(vertex_index)] two: Input<i32>) { }

Right now, this code does consider name to be part of the unique key of an OpVariable - so it will not deduplicate the above, and keep two around.

Amusingly, I got this idea from a completely unrelated issue with a community member having issues with I think spirv-cross, which dumped out two identical variables in the source (because there's two OpVariables), which got sad. Context in the arkadia discord here.