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The following changes cleanup the eval loop and result in a pretty solid 2 to 3% improvement in pybench for me.
And it is about 5% faster for long generators.
* Change why enum type to int and #defines. And moved the why defines to opcode.h so that they can be seen by the genrator objects after a yield, return, or exception.
* Added an "int f_why" to frames so the generator can see why it returned from a send.
* Refactored generator obj so it can use the "f->f_why" to determine what to do without having to do several checks first.
* Moved the generator specific execption save/swap/and clear out of the cevel main loop. No need to check for those on every function call.
The only test that fails is the frame size is test_sys. I left that in for now so someone could check that, and tell me if it's ok to fix it, or if I need to do something else.
I also considered putting the why on the tstate object. It might save some memory as there wouldn't be as many of those.