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Miscompilation introduced by CopyPropagation #76740

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tmiasko opened this issue Sep 15, 2020 · 2 comments · Fixed by #77373
Closed

Miscompilation introduced by CopyPropagation #76740

tmiasko opened this issue Sep 15, 2020 · 2 comments · Fixed by #77373
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A-mir-opt Area: MIR optimizations C-bug Category: This is a bug. I-unsound Issue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@tmiasko
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tmiasko commented Sep 15, 2020

To reproduce the issue:

  • Checkout 41dc394 (for reproducibility, but might be unnecessary).
  • Enable copy propagation so that it runs on mir-opt-level=1.
  • ./x.py test --stage 2 src/test/ui (disable incremental compilation, so that rustc is rebuild completely).
  • Observe tests failures: "not all trait items implemented, missing ...".
@tmiasko tmiasko added the C-bug Category: This is a bug. label Sep 15, 2020
@jonas-schievink jonas-schievink added A-mir-opt Area: MIR optimizations I-unsound Issue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness requires-nightly This issue requires a nightly compiler in some way. labels Sep 15, 2020
@tmiasko tmiasko mentioned this issue Sep 15, 2020
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@jyn514 jyn514 added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Sep 15, 2020
@tmiasko
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tmiasko commented Sep 20, 2020

The copy propagation incorrectly assumes that a use of a local in Operand::Move will not mutate it.

@jonas-schievink
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#72632 has landed now, so we could remove CopyPropagation and focus on that instead

@jonas-schievink jonas-schievink mentioned this issue Sep 30, 2020
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@bors bors closed this as completed in ffeeb20 Oct 17, 2020
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A-mir-opt Area: MIR optimizations C-bug Category: This is a bug. I-unsound Issue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Remove the old copy propagation pass
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@jonas-schievink @jyn514 @tmiasko