CALL_FUNCTION can be specialized. Copying from Mark's comments https://github.com/faster-cpython/ideas/issues/54#issue-898013125
```
There are a number of specializations of CALL_FUNCTION that make sense:
1. Calls to a Python function where the arguments and parameters match exactly.
2. Calls to a Python function with keyword arguments, or defaults, when the argument shuffle can be pre-computed.
3. Calls to builtin functions.
4. Calls to specific builtin functions, specifically len and instance.
5. Calls to type with a single argument.
6. Instantiation of a "normal" class, that is a class that does not redefine __new__ and whose metaclass is type.
```
I've prepared a PR that should speed up non-keyword calls to PyCFunction. It covers specializations 3 and 4. Stable pyperf microbenchmarks show 5-15% less call overhead for some PyCFunctions. Please see https://github.com/faster-cpython/ideas/issues/54#issuecomment-868978681 for the benchmark script and results.
This issue is also tied to issue44207 (Add a version number to Python functions) which will be required for specializations 1 and 2.
Unfortunately, PR 26934 has broken thes 390x RHEL7 LTO 3.x buildbot as you can see before. As per the buildbot maintenance procedures, we will need to revert this PR unless is fixed in 24 hours.
@markshannon @Fidget-Spinner