Your criticisms may very well be true. IIRC though, I wrote that pass because what was available was not general enough. The stackdepth_walk function made assumptions that, while true of code generated by the current cpython frontend, were not universally true. If a goal is to move this calculation after any bytecode optimization, something along these lines seems like it will eventually be necessary.
 
Anyway, just offering things already written. If you don't feel it's useful, no worries.
 
 
On Wed, May 18, 2016, at 11:35 AM, Cesare Di Mauro wrote:
2016-05-17 8:25 GMT+02:00 <zreed@fastmail.com>:
In the project https://github.com/zachariahreed/byteasm I mentioned on
the list earlier this month, I have a pass that to computes stack usage
for a given sequence of bytecodes. It seems to be a fair bit more
agressive than cpython. Maybe it's more generally useful. It's pure
python rather than C though.
 
IMO it's too big, resource hungry, and slower, even if you convert it in C.
 
If you take a look at the current stackdepth_walk function which CPython uses, it's much smaller (not even 50 lines in simple C code) and quite efficient.
 
Currently the problem is that it doesn't return the maximum depth of the tree, but it updates the intermediate/current maximum, and *then* it uses it for the subsequent calculations. So, the depth artificially grows, like in the reported cases.
 
It doesn't require a complete rewrite, but spending some time for fine-tuning it.
 
Regards
Cesare