Inada Naoki <songofaca...@gmail.com> added the comment:
FWIW, it seems -O0 don't merge local variables in different path or lifetime.
For example, see _Py_abspath
```
if (path[0] == '\0' || !wcscmp(path, L".")) {
wchar_t cwd[MAXPATHLEN + 1];
//(snip)
}
//(snip)
wchar_t cwd[MAXPATHLEN + 1];
```
wchar_t is 4bytes and MAXPATHLEN is 4096 on Linux. So each cwd is 16388bytes.
-Og allocates 32856 bytes for it and -Og allocates 16440 bytes for it.
I don't know what is the specific optimization flag in -Og do merge local
variable, but I think -Og is very important for _PyEval_EvalFrameDefault()
since it has many local variables in huge switch-case statements.
-Og allocates 312 bytes for it and -O0 allocates 8280 bytes for it.
By the way, clang 13 has `-fstack-usage` option like gcc, but clang 12 don't
have it.
Since Ubuntu 20.04 have only clang 12, I use `-fstack-size-segment` and
https://github.com/mvanotti/stack-sizes to get stack size.
----------
nosy: +methane
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