Wasmtime GitHub notifications bot (Feb 05 2022 at 03:56): Wasmtime GitHub notifications bot (Feb 05 2022 at 03:56):cfallin requested fitzgen for a review on PR #3769.
Wasmtime GitHub notifications bot (Feb 05 2022 at 03:56):cfallin opened PR #3769 from fix-debuginfo-cold-blocks to main:
The debuginfo analyses are written with the assumption that the order of
instructions in the VCode is the order of instructions in the final
machine ocde. This was previously a strong invariant, until we
introduced support for cold blocks. Cold blocks are implemented by
reordering during emission, because the VCode ordering has other
requirements related to lowering (responding def-use dependencies in the
reverse pass), so it is much simpler to reorder instructions at the last
moment. Unfortunately, this causes the breakage we now see.This commit fixes the issue by skipping all cold instructions when
emitting value-label ranges (which are translated into debuginfo). This
means that variables defined in cold blocks will not have DWARF
metadata. But cold blocks are usually compiler-inserted slowpaths, not
user code, so this is probably OK. Debuginfo is always best-effort, so
in any case this does not violate any correctness constraints.Discovered while debugging a test failure in #3733.
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Wasmtime GitHub notifications bot (Feb 05 2022 at 06:33):cfallin updated PR #3769 from fix-debuginfo-cold-blocks to main.
Wasmtime GitHub notifications bot (Feb 05 2022 at 07:11):cfallin updated PR #3769 from fix-debuginfo-cold-blocks to main.
Wasmtime GitHub notifications bot (Feb 05 2022 at 07:13):cfallin updated PR #3769 from fix-debuginfo-cold-blocks to main.
Wasmtime GitHub notifications bot (Feb 05 2022 at 07:14):cfallin edited PR #3769 from fix-debuginfo-cold-blocks to main:
The debuginfo analyses are written with the assumption that the order of
instructions in the VCode is the order of instructions in the final
machine ocde. This was previously a strong invariant, until we
introduced support for cold blocks. Cold blocks are implemented by
reordering during emission, because the VCode ordering has other
requirements related to lowering (respecting def-use dependencies in the
reverse pass), so it is much simpler to reorder instructions at the last
moment. Unfortunately, this causes the breakage we now see.This commit fixes the issue by skipping all cold instructions when
emitting value-label ranges (which are translated into debuginfo). This
means that variables defined in cold blocks will not have DWARF
metadata. But cold blocks are usually compiler-inserted slowpaths, not
user code, so this is probably OK. Debuginfo is always best-effort, so
in any case this does not violate any correctness constraints.Discovered while debugging a test failure in #3733.
<!--
Please ensure that the following steps are all taken care of before submitting
the PR.
[ ] This has been discussed in issue #..., or if not, please tell us why
here.[ ] A short description of what this does, why it is needed; if the
description becomes long, the matter should probably be discussed in an issue
first.[ ] This PR contains test cases, if meaningful.
- [ ] A reviewer from the core maintainer team has been assigned for this PR.
If you don't know who could review this, please indicate so. The list of
suggested reviewers on the right can help you.Please ensure all communication adheres to the code of conduct.
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Wasmtime GitHub notifications bot (Feb 05 2022 at 07:15):cfallin updated PR #3769 from fix-debuginfo-cold-blocks to main.
Wasmtime GitHub notifications bot (Feb 07 2022 at 16:58):fitzgen submitted PR review.
Wasmtime GitHub notifications bot (Feb 07 2022 at 16:58):fitzgen merged PR #3769.
Last updated: Dec 23 2024 at 12:05 UTC