Transition to arraycontext

[alexfikl]

Get sumpy on array contexts as well! This eats up the first commit from #118.

Porting individual files

• Pass tests!
  • test_codegen
  • test_cse
  • test_distributed
  • test_fmm
  • test_kernels
  • test_matrixgen
  • test_misc
  • test_qbx
  • test_tools
• Port examples!
  • curve-pot
  • curve
  • expansion-toys
  • fourier
  • sym-exp-complexity

Remaining porting issues

• Move caching to the array context from KernelCacheMixin.
• Handle kernel optimizations.
  • Currently it uses get_cached_executor(), which branches on OPT_ENABLED, but we need to move to actx.call_loopy.
  • Move to transform_loopy_program? Would need to also add some fancy tags or something to customize it?
• Need to move e.g. register_optimization_preambles to the array context somehow too.
  • The kernels no longer have a context or device, so they can't do that.
  • Probably need to move this to actx.transform_loopy_program somehow?

Upstream / downstream PRs

• Depends on Transition to arraycontext boxtree#56
• Depends on Fix TranslationUnit._hash_value disappearing during pickling loopy#677
• Depends on: Updated sumpy and boxtree to arraycontext branches pytential#179

Speculative TODOs

• Should some classes clone the actx? Here e.g. SumpyTreeIndependentDataForWrangler but also in boxtree.
  • The big worry is that cloning throws away any caches on the actx.
  • Pretty much all *Builder classes can be functions + all other memoized kernels can be functions, but should leave that for later since it can be done without breaking the world.
• Rip out the timing stuff (not sure, just mentioned by @inducer at some point).
  • This would also need to be done in boxtree?
• Add an array context to do the timing stuff? (likely for a future PR)

[inducer]

FYI I'm somewhere half-way resolving conflicts in this.

[inducer]

Not sure I love that an explicit actx argument is necessary now. It might be better to have the actx globally in the toy context.

[alexfikl]

I'm very fine with that! Don't recall if I had any particular reason to make it explicit to each function (possibly to match P2P.__call__ and friends?).

[inducer]

Draft merge in #256.

[inducer]

Continued in #256, closing here, since I can't seem to force-push here.