LOAD_CONST_IMMORTAL doesn't survive being instrumented and de-instrumented.

[markshannon]

Bug report

Bug description:

When instrumenting, instructions are first de-optimized to their base instruction.
When instrumentation is removed we assume that specialization will restore the specialized instruction.
However, that doesn't happen for LOAD_CONST_IMMORTAL because LOAD_CONST_IMMORTAL isn't a specialization form of LOAD_CONST, but a quickened form of it.

The fix should be simple. Instead of quickening LOAD_CONST to LOAD_CONST_IMMORTAL, we add a LOAD_CONST_MORTAL and have LOAD_CONST specialize (rather than quicken) to either LOAD_CONST_MORTAL or LOAD_CONST_IMMORTAL.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response