Unswitching adjusts the CFG in ways that may invalidate cached loop
dispositions. Clear all cached block and loop dispositions during
trivial unswitching. The same is already done for non-trivial
unswitching.
Fixes#58751.
SimpleLoopUnswitch may remove blocks from loops. Clear block and loop
dispositions in that case, to clean up invalid entries in the cache.
Fixes#58158.
Fixes#58159.
This simplifies the test case added in e399dd601 to only require indvars
and simple-loop-unswitch. This allows adding the test case for #58158 to
the same file, keeping related tests together.
