gh-91421: Use constant value check during runtime by stoeckmann · Pull Request #91422

gh-91421: Use constant value check during runtime by stoeckmann · Pull Request #91422 · python/cpython

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The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Fixes issue #91421.

All commit authors signed the Contributor License Agreement.

stoeckmann changed the title ~~Use constant value check during runtime~~ gh-91421: Use constant value check during runtime

Apr 10, 2022

Thanks, this looks right to me but I'll leave others some time to speak up if there's something I missed.

This will need a NEWS entry, which you can add using blurb: https://devguide.python.org/?highlight=blurb#quick-reference. We're still working on updating some bpo references there, but I believe the blurb-it online tool has already been updated to point to GitHub.

The blurb-it web tool required a bpo, but the command line tool blurb was already adjusted.

This looks good. One assembly instruction can be reduced.

		@@ -0,0 +1 @@
		Use constant value check during runtime in _Py_DecodeUTF8Ex.

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	Use constant value check during runtime in _Py_DecodeUTF8Ex.
	Fix a potential integer overflow in _Py_DecodeUTF8Ex.

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Adjusted.

The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Thanks @stoeckmann for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9, 3.10.
🐍🍒⛏🤖

miss-islington pushed a commit to miss-islington/cpython that referenced this issue

Apr 13, 2022

The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Fixes pythonGH-91421.
(cherry picked from commit 0859368)

Co-authored-by: Tobias Stoeckmann <stoeckmann@users.noreply.github.com>

gvanrossum pushed a commit to gvanrossum/cpython that referenced this issue

Apr 13, 2022

The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Fixes pythonGH-91421.

JelleZijlstra pushed a commit that referenced this issue

Apr 14, 2022

The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Fixes GH-91421.
(cherry picked from commit 0859368)

Co-authored-by: Tobias Stoeckmann <stoeckmann@users.noreply.github.com>

JelleZijlstra pushed a commit that referenced this issue

Apr 14, 2022

The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Fixes GH-91421.
(cherry picked from commit 0859368)

Co-authored-by: Tobias Stoeckmann <stoeckmann@users.noreply.github.com>