bpo-43846: Use less stack for large literals and calls #25403
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gvanrossum
approved these changes
Apr 14, 2021
Python/compile.c
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| if (n+pushed >= STACK_USE_GUIDELINE) { | ||
| ADDOP_I(c, build, pushed); | ||
| seen_star = 1; | ||
| } | ||
| else { | ||
| seen_star = 0; | ||
| } |
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Hm, I suppose you could just set seen_star = 0 here and emit the push in the for-loop below when i+n exceeds the limit (and it hasn't been emitted yet). FWIW I wish during this phase the variable was called something like 'build_emitted', since that is really what it's keeping track of.
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Done.
I used sequence_built and also cleaned up the surrounding code a bit.
| ADDOP_I(c, BUILD_STRING, asdl_seq_LEN(e->v.JoinedStr.values)); | ||
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| Py_ssize_t value_count = asdl_seq_LEN(e->v.JoinedStr.values); | ||
| if (value_count > STACK_USE_GUIDELINE) { |
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Maybe use >= for consistency with earlier locations?
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I've used > throughout. It seems to fit better with STACK_USE_GUIDELINE being the maximum stack use.
Python/compile.c
Outdated
| @@ -4251,7 +4329,8 @@ compiler_subkwargs(struct compiler *c, asdl_keyword_seq *keywords, Py_ssize_t be | |||
| keyword_ty kw; | |||
| PyObject *keys, *key; | |||
| assert(n > 0); | |||
| if (n > 1) { | |||
| int big = n > STACK_USE_GUIDELINE/2; | |||
…DELINE use the same comparison.
kreathon
pushed a commit
to kreathon/cpython
that referenced
this pull request
May 2, 2021
* Modify compiler to reduce stack consumption for large expressions. * Add more tests for stack usage. * Add NEWS item. * Raise SystemError for truly excessive stack use.
This was referenced Jun 27, 2022
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Prevents excessive stack usage for oversized calls and literals.
Having a soft upper limit on stack usage allows us to design more efficient stack layouts
without worrying about code that uses huge amounts of stack.
As giant literals and calls are rare, this PR should have negligible effect on performance.
https://bugs.python.org/issue43846