nested mme_while leads to failing cts cases

When trying some things with the mme I found something that I do not understand regarding nested loops and whiles.

@jekstrand confirmed on irc that nested loops does not work but whiles do. I also wrote a small unit test with two nested whiles that passes. There should not be a problem.

However this was not what I observed when trying things in the drawing code.

One example is for indirect indexed draws. Here nvk_mme_draw_indexed_indirect() uses a mme_while over draw_count. In this while it calls nvk_mme_build_draw_indexed(). This function does a mme_loop over instance_count. CTS tests pass. Switching between loop and while in the two functions resulted in:

nvk_mme_draw_indexed_indirect	nvk_mme_build_draw_indexed	CTS
Loop	While	Pass
Loop	Loop	Fail
While	Loop	Pass
While	While	Fail

Why using while in both functions would make the CTS fail I do not understand. I have tried to debug this but I cannot find the answer.

Several cts cases are affected. In this specific setup I was testing dEQP-VK.draw.renderpass.indirect_draw.indexed_data_from_compute.indirect_draw_instanced*