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ICE: Adding -C save-temps to incremental compile causes rustc_codegen_ssa::back::write panic #66367

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#160781
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ICE: Adding -C save-temps to incremental compile causes rustc_codegen_ssa::back::write panic#66367
#160781
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zakrad
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A-incr-compArea: Incremental compilationC-bugCategory: This is a bug.E-needs-testCall for participation: An issue has been fixed and does not reproduce, but no test has been added.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️P-mediumMedium priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.glacierICE tracked in rust-lang/glacier.

Description

@pnkfelix
pnkfelix
opened on Nov 13, 2019

Steps to reproduce:

% mkdir temp
% cd temp
% touch lib.rs
% rustc +nightly lib.rs --crate-type=lib -C incremental=incr
% rustc +nightly lib.rs --crate-type=lib -C incremental=incr -C save-temps
thread '<unnamed>' panicked at 'assertion failed: `(left == right)`
  left: `false`,
 right: `true`', src/librustc_codegen_ssa/back/write.rs:872:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.40.0-nightly (50f8aadd7 2019-11-07) running on x86_64-unknown-linux-gnu

note: compiler flags: -C incremental -C save-temps --crate-type lib

thread '<unnamed>' panicked at 'src/librustc_codegen_ssa/back/write.rs:1488: worker thread panicked', src/librustc/util/bug.rs:37:26

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.40.0-nightly (50f8aadd7 2019-11-07) running on x86_64-unknown-linux-gnu

note: compiler flags: -C incremental -C save-temps --crate-type lib

thread 'rustc' panicked at 'src/librustc_codegen_ssa/back/write.rs:1758: panic during codegen/LLVM phase', src/librustc/util/bug.rs:\
37:26

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.40.0-nightly (50f8aadd7 2019-11-07) running on x86_64-unknown-linux-gnu

note: compiler flags: -C incremental -C save-temps --crate-type lib

Activity

  1. pnkfelix commented on Nov 13, 2019

    @pnkfelix
    pnkfelix
    on Nov 13, 2019
    ContributorAuthor

    (the workaround is to make sure you start with -C save-temps in your initial command line. I assume you need to subsequently keep it around to avoid another ICE, but I have not verified that.)

  2. pnkfelix
    added
    A-incr-compArea: Incremental compilation
    I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    P-mediumMedium priority
    on Nov 13, 2019
  3. pnkfelix
    self-assigned this
    on Nov 13, 2019
  4. jonas-schievink
    added
    C-bugCategory: This is a bug.
    on Nov 13, 2019
  5. rust-lang-glacier-bot
    added
    glacierICE tracked in rust-lang/glacier.
    on Nov 18, 2019

  6. pnkfelix commented on Dec 23, 2019

    @pnkfelix
    pnkfelix
    on Dec 23, 2019
    ContributorAuthor

    (also, the reported "compiler flags" in the diagnostic says -C incremental when the actual option was -C incremental=incr. A subtle difference but I bet it would mean the world to some people trying to debug something...)

  7. pnkfelix commented on Dec 23, 2019

    @pnkfelix
    pnkfelix
    on Dec 23, 2019
    ContributorAuthor

    The panic is due to this assert failure in execute_copy_from_cache_work_item:

    rust/src/librustc_codegen_ssa/back/write.rs

    Line 868 in a916ac2

    assert_eq!(bytecode.is_some(), module_config.emit_bc);

    My first instinct was to try to revise the logic so that we would force the code generation of the bytecode when -C save-temps is added to the command line.

    But after thinking about it more, I do not think that is the appropriate fix. Someone adding -C save-temps probably is trying to understand the current compiler invocation. Having -C save-temps cause it to go through significantly new code paths (i.e. generating new code when previously it would have just reused existing object files) does not sound right to me.

    So the question is, what is the correct fix here?

    I can imagine:

    1. turn the assert into a normal error, with a diagnostic like: "emit LLVM bytecode requested, but no bytecode file found in incremental cache",
    2. or get rid of the assert entirely; maybe nothing further down in the control flow depends on the property being asserted there? Wishful thinking, I know.

    @michaelwoerister , any thoughts here? And also cc @alexcrichton, whom I believe is the source for these assertions way back in 8197a0b

  8. alexcrichton commented on Jan 6, 2020

    @alexcrichton
    alexcrichton
    on Jan 6, 2020
    Member

    I would agree that the intention of save-temps is "just don't delete temporary files you would otherwise delete" and is really only used for debugging. In that sense I think it's fine to basically get rid of this assert personally.

  9. michaelwoerister commented on Jan 13, 2020

    @michaelwoerister
    michaelwoerister
    on Jan 13, 2020
    Member

    Getting rid of the assertion seems fine.

  10. JohnTitor commented on May 6, 2020

    @JohnTitor
    JohnTitor
    on May 6, 2020
    Member

    The assertion was removed by #71754.

  11. Enselic commented on Aug 24, 2023

    @Enselic
    Enselic
    on Aug 24, 2023
    Member

    Triage: Seems quite easy to add a regression test for this ICE so it can be closed. See ./tests/incremental for examples of incremental tests.

    @rustbot label E-needs-test

  12. rustbot
    added
    E-needs-testCall for participation: An issue has been fixed and does not reproduce, but no test has been added.
    on Aug 24, 2023
  13. Noratrieb
    unassigned
    pnkfelix
    on Aug 2, 2025

  14. zakrad commented on Aug 8, 2026

    @zakrad
    zakrad
    on Aug 8, 2026
    Contributor

    @rustbot claim

  15. rustbot
    assigned
    zakrad
    on Aug 8, 2026
  16. jhpratt
    added a commit that references this issue on Aug 9, 2026

    Rollup merge of rust-lang#160781 - zakrad:regr-test-66367, r=mejrs

    dc4b231
  17. JonathanBrouwer
    added 2 commits that reference this issue on Aug 9, 2026

    Rollup merge of rust-lang#160781 - zakrad:regr-test-66367, r=mejrs

    caab99c

    Rollup merge of rust-lang#160781 - zakrad:regr-test-66367, r=mejrs

    374ec00
  18. rust-bors
    closed this as completedin 374ec00on Aug 9, 2026
  19. rust-timer
    added a commit that references this issue on Aug 9, 2026

    Unrolled build for #160781

    35f23da
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A-incr-compArea: Incremental compilationC-bugCategory: This is a bug.E-needs-testCall for participation: An issue has been fixed and does not reproduce, but no test has been added.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️P-mediumMedium priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.glacierICE tracked in rust-lang/glacier.

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