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GH-112354: `END_FOR` instruction to only pop one value. by markshannon · Pull Request #114247 · python/cpython · GitHub

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GH-112354: END_FOR instruction to only pop one value. - #114247

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markshannon merged 8 commits into
python:mainfrom
faster-cpython:split-end-for
Jan 24, 2024
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GH-112354: END_FOR instruction to only pop one value.#114247
markshannon merged 8 commits into
python:mainfrom
faster-cpython:split-end-for

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markshannon commented Jan 18, 2024 •
edited by bedevere-app Bot
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In order to support tier 2 side-exits from FOR_ITER variants, we need a target that has the same stack as the exhaustion guard.
Currently we can either jump to the END_FOR, as we do for generators or the instruction afterwards, which we do for FOR_ITER.
In order to exit a guard we need a target in between those instructions, that pops the iterator, but not the value.
The compiler emits END_FOR; POP_TOP instead of END_FOR.
Previously:

   END_FOR (Pops two values) <- FOR_ITEN_GEN targets this
   ...                       <- FOR_ITER targets this

Now:

   END_FOR (Pops one value)  <- FOR_ITEN_GEN targets this
   POP_TOP (Pops one value)  <- _GUARD_NOT_EXHAUSTED can target this
   ...                       <- FOR_ITER targets this

bedevere-app Bot mentioned this pull request Jan 18, 2024
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gvanrossum commented Jan 18, 2024 •
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Maybe we can do without a separate END_FOR opcode and instead just generate a POP_TOP?

EDIT: Never mind, it's needed for instrumentation.

gvanrossum approved these changes Jan 18, 2024
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Looks good, never mind my premature commend about END_FOR/POP_TOP.

Comment thread Include/internal/pycore_unicodeobject_generated.h
Comment on lines +672 to +674
string = &_Py_ID(alias);
assert(_PyUnicode_CheckConsistency(string, 1));
_PyUnicode_InternInPlace(interp, &string);

gvanrossum Jan 18, 2024

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

(The updates to this file (and a few other generated files) are spurious and will disappear after merging the latest main.)

markshannon commented Jan 19, 2024

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The benchmarks show no performance impact.

markshannon commented Jan 19, 2024

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EDIT: Never mind, it's needed for instrumentation.

That's evidently not clear. The order of the POP_TOP and END_FOR is important as well.
I'll add some comments.

gvanrossum approved these changes Jan 19, 2024
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Thanks!

brettcannon removed their request for review January 19, 2024 18:31

gvanrossum commented Jan 22, 2024

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Oh, fun stuff. Windows compilation error. :-(

markshannon merged commit 981d172 into python:main Jan 24, 2024
Eclips4 mentioned this pull request Jan 25, 2024
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markshannon deleted the split-end-for branch February 1, 2024 19:50
aisk pushed a commit to aisk/cpython that referenced this pull request Feb 11, 2024
pythonGH-112354: END_FOR instruction to only pop one value. (python…
b18aa09 
…GH-114247)

* Compiler emits END_FOR; POP_TOP instead of END_FOR. To support tier 2 side exits in loops.
Glyphack pushed a commit to Glyphack/cpython that referenced this pull request Sep 2, 2024
pythonGH-112354: END_FOR instruction to only pop one value. (python…
58dc25a 
…GH-114247)

* Compiler emits END_FOR; POP_TOP instead of END_FOR. To support tier 2 side exits in loops.
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