The confusion here was around a test that was testing the behavior when one
/does not/ guard a polymorphic builtin with a _isConcrete. Specifically, without
_isConcrete, one gets weird behavior where in debug we crash, but in release we
may not due to further inlining/specialization. With _isConcrete, we never
crashand get the appropriate behavior.
This commit works by changing the current run of the polymorphic builtin test to
force -Onone and adds an extra -O run that way we validate both behaviors.
I forgot about this part of the design when I was working on this. To ensure
that the whole design works as expected, I included a small end-to-end test
using an experimental design for simd that uses polymorphic builtins that test
this functionally.
NOTE: The experimental design is only intended to exercise the code functionally.
rdar://48248417
