Structured Control Flow

[VZout]

For non-kernel shaders SPIR-V requires you to mark structured control flow with merge instructions.

Primary Tasks:

• Conditional Branch
• Loops - in progress
  • break (partially unreachable)
  • break (fully unreachable)
  • continue
  • return
• Switch

Secondary Tasks:

• Find convergence points using post-dominator tree algorithm instead of my approach.
• Optimize loop detection.
• Reduce duplicate code.

Backlog:

• "make reducible" pass.
  • The MIR generated from rust is currently reducible. This might change in the future or we might have missed a corner case.

[Maaarcocr]

Hey! I know that loops are in progress, but I would be happy to help with them if there was any subtask that you may want to offload to an open source contributor!

I have some experience with structured control flow, in the past I've worked on a SPMD pass on top of the Julia IR. I'll also be more than happy to work on switch!

[khyperia]

Reminder for us: NO_DCE=1 is broken right now (hangs for a long time - infinitely? - in the structurization pass). We should add NO_DCE=1 to tests once we fix that.

[VZout]

Hey! I know that loops are in progress, but I would be happy to help with them if there was any subtask that you may want to offload to an open source contributor!

I have some experience with structured control flow, in the past I've worked on a SPMD pass on top of the Julia IR. I'll also be more than happy to work on switch!

Hey thanks for the offer. I expect to get loops and switches in before the end of the week. But if you want to look into creating a irreducible -> reducible pass that would be very helpful for us in the future. However I believe the plan is to strip the structuration pass and put it into SPIRV-TOOLS once we have the reducible pass since it may be off help to many more people. If you want to talk more in-depth you can always talk to me on the Embark discord.