On Wed, Mar 02, 2022 at 09:25:01AM -0500, Ricky Teachey wrote:
> Is there some opportunity for some kind of compiler magic when the iterable
> of a for loop is fully contained in a place easily findable by the
> compiler, and not spread over multiple if and for statements?
I am not an expert on compiler optimization techniques, but I would be
very surprised if something as minor as a computation being split over
two statements instead of one would make a difference.
What would make a difference would be statements *between* the for and
the if:
# some hypothetical optimization may apply
for spam in eggs:
if cheese:
block
# may block the optimization
for spam in eggs:
block
if cheese:
block
but even there, a *sufficiently smart* optimizer may be able to do some
pretty wild things. This is why, for instance, optimizing C compilers
can often completely reorder your code.
https://stackoverflow.com/questions/26190364/is-it-legal-for-a-c-optimizer-to-reorder-calls-to-clock
In a practical sense, given the relatively limited human and financial
resources available to Python compared to C, it might be slightly easier
for *people* to program an optimizer to spot the opportunity in the
single statement case compared to the two statement case.
But even there, I doubt it -- optimization is unlikely to occur at the
source code level, more likely at the AST or even bytecode level, where
any such difference between 1 vs 2 statements is likely to disappear.
--
Steve
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