> Both changes add significant amount of code (100 and 85 lines correspondingly). Even if they speed up a particular case of dict constructor it is not common use case.

You are right, but please wait.

Marco is new contributor and he can write correct C code for now.
So I am searching some parts which can be optimized by his code before rejecting it.

* bpo-42126, GH-22911: I can make dict display (aka. dict literal) 50% faster. But it introduce additional complexity to compiler and ceval. So I will reject it unless I find real world code using dict display in performance critical part.

* _PyStack_AsDict (https://github.com/methane/cpython/pull/25): I thought this is performance critical function. But I could not see significant performance gain in pyperformance.

* _PyEval_EvalCode (https://github.com/python/cpython/blob/master/Python/ceval.c#L4465): I am still not sure we can assume there are no duplicated keyword argument here. If we can assume it, we can optimize calling function receiving **kwds argument.

These three parts are all I found. I will reject this issue after I failed to optimize _PyEval_EvalCode.