The pocl compilation time for the ACA kernel is bizarrely long.

[tbenthompson]

Most of the OpenCL kernels seem to take about 1-3 seconds to compile with pocl. But, aca.cu takes almost three minutes. The is true on both my machine and the github actions CI servers so I suspect it will replicate elsewhere too.

Ideas:

• Maybe the problem is just an issue with the pocl conda package and is due to some misconfigured LLVM flags. See here where this issue is suggested: http://portablecl.org/docs/html/faq.html#why-is-pocl-slow
• The problem vanishes if I turn off optimization flags using -cl-opt-disable. I would actually be okay leaving this flag on all the time. But, that caused some segfault errors! I'm not sure what the problem is there.
• Obviously the Mako code generation is producing a lot of code, but it's not substantially more code in aca.cu compared to the other kernels like free.cu or block.cu. So, what is causing the compiler to burp here?