[Cython] Exception check optimization

[Stefan Behnel]

Am 30.05.2013 14:38, schrieb Nikita Nemkin:
> On Thu, 30 May 2013 08:25:55 +0600, Robert Bradshaw wrote:
>> On Sun, May 26, 2013 at 10:04 AM, Nikita Nemkin wrote:
>>> I wonder why is __pyx_filename (in exception check blocks)
>>> tracked dynamically? AFAIK it's impossible to split function
>>> body between multiple files (include only works at the top level),
>>> which makes filename a compile time constant for any given function.

What about includes? Are they allowed inside of functions? If not, then
this sounds like a safe assumption.

If they are allowed, then it should still be possible to special case
the file name setting, i.e. set it to the default at function entry and
only set it to a different value if it happens to change inside of a
function. The C compiler should often (normally?) be smart enough to
eliminate the constant assignment.


>>> If the above is correct, __pyx_filename variable can be eliminated,
>>> saving at least 5 bytes per exception check (more on x64).
>>
>> Probably because exception checks are heavy-weight enough that we
>> haven't bothered optimizing them at this level yet.
> 
> By "exception checks" I mean these things:
> 
> if (unlikely(!__pyx_t_2)) {__pyx_filename = __pyx_f[0]; __pyx_lineno =
> 15; __pyx_clineno = __LINE__; goto __pyx_L1_error;}
> 
> They are fast, but the problem is the extra code: neither
> __pyx_filename nor __pyx_clineno assignments are necessary.
> Removing them reduces binary size by 2-3%.
> 
> If you're OK with it, I'll make a patch that removes __pyx_filename
> and disables __pyx_clineno by default.

I'm fine with both. I consider seeing the C line a debug feature that
people shouldn't need normally.

Stefan