Hi Pablo,
On 29/10/2020 11:08 am, Pablo Galindo Salgado wrote:
> The new semantics may well result in some slowdowns. That's stated in
the PEP.I don't think I can reliably isolate the effects of the (very
slight)
change in the behavior of f_lineno.
Ok, then let's make at least we measure the general slowdowns.
Except that we can't measure the performance of a specification.
We can only measure the performance of entire implementations.
I can make an implementation that conforms to PEP 626 that is slower
than master, or I can make one that's faster :)
It doesn't change the value of the PEP itself.
Let me give you a toy example.
def f():
while 1:
body()
3.9 compiles this to:
(The trailing, implicit return has been stripped for clarity)
3 >> 0 LOAD_GLOBAL 0 (body)
2 CALL_FUNCTION 0
4 POP_TOP
6 JUMP_ABSOLUTE 0
A naive implementation that conforms to PEP 626 would this compile to:
2 >> 0 NOP
3 2 LOAD_GLOBAL 0 (body)
4 CALL_FUNCTION 0
6 POP_TOP
8 JUMP_ABSOLUTE 0
But a better implementation could produce this:
2 0 NOP
3 >> 2 LOAD_GLOBAL 0 (body)
4 CALL_FUNCTION 0
6 POP_TOP
2 8 JUMP_ABSOLUTE 2
Which has the same bytecodes as 3.9 in the loop, and has the correct
line numbers.
Cheers,
Mark.
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