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Zalathar opened this issue Oct 17, 2024 · 3 comments
Closed
1 of 3 tasks

Remove unstable -Zprofile (gcov-style coverage) #798

Zalathar opened this issue Oct 17, 2024 · 3 comments
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major-change A proposal to make a major change to rustc major-change-accepted A major change proposal that was accepted T-compiler Add this label so rfcbot knows to poll the compiler team

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@Zalathar
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Zalathar commented Oct 17, 2024 •
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Proposal

There is an unstable -Zprofile flag that enables “gcov-style” coverage instrumentation.

(The profile flag predates and is separate from the stable -Cinstrument-coverage flag.)

Notably, the -Zprofile flag:

  • Is largely untested in-tree, having only one run-make test that does not check whether its output is correct or useful.
  • Has no known maintainer.
  • Has seen no push towards stabilization.
  • Has at least one severe regression reported in 2022 that apparently remains unaddressed.
  • Is confusingly named, since it appears to be more about coverage than performance profiling, and has nothing to do with PGO.
  • Is fundamentally limited by relying on counters auto-inserted by LLVM, with no knowledge of Rust beyond debuginfo.

I propose to remove this unstable flag (and its accompanying -Zprofile-emit), implemented at:

Mentors or Reviewers

—

Process

The main points of the Major Change Process are as follows:

  • File an issue describing the proposal.
  • A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
    • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
    • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
  • Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.
@Zalathar Zalathar added major-change A proposal to make a major change to rustc T-compiler Add this label so rfcbot knows to poll the compiler team labels Oct 17, 2024
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rustbot commented Oct 17, 2024

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

Concerns or objections to the proposal should be discussed on Zulip and formally registered here by adding a comment with the following syntax:

@rustbot concern reason-for-concern 
<description of the concern>

Concerns can be lifted with:

@rustbot resolve reason-for-concern

See documentation at https://forge.rust-lang.org

cc @rust-lang/compiler @rust-lang/compiler-contributors

@rustbot rustbot added the to-announce Announce this issue on triage meeting label Oct 17, 2024
@Zalathar Zalathar mentioned this issue Oct 17, 2024
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@jieyouxu
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@rustbot second

@rustbot rustbot added the final-comment-period The FCP has started, most (if not all) team members are in agreement label Oct 17, 2024
@apiraino apiraino removed the to-announce Announce this issue on triage meeting label Oct 17, 2024
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@rustbot label -final-comment-period +major-change-accepted

@rustbot rustbot added major-change-accepted A major change proposal that was accepted to-announce Announce this issue on triage meeting and removed final-comment-period The FCP has started, most (if not all) team members are in agreement labels Oct 30, 2024
@apiraino apiraino removed the to-announce Announce this issue on triage meeting label Oct 31, 2024
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 1, 2024
@matthiaskrgr
Rollup merge of rust-lang#131829 - Zalathar:goodbye-zprofile, r=cheny…
11a09d4 
…ukang

Remove support for `-Zprofile` (gcov-style coverage instrumentation)

Tracking issue: rust-lang#42524

MCP: rust-lang/compiler-team#798

---

This PR removes the unstable `-Zprofile` flag, which enables ”gcov-style” coverage instrumentation, along with its associated `-Zprofile-emit` configuration flag.

(The profile flag predates and is almost entirely separate from the stable `-Cinstrument-coverage` flag.)

Notably, the `-Zprofile` flag:
- Is largely untested in-tree, having only one run-make test that does not check whether its output is correct or useful.
- Has no known maintainer.
- Has seen no push towards stabilization.
- Has at least one severe regression reported in 2022 that apparently remains unaddressed.
  - rust-lang#100125
- Is confusingly named, since it appears to be more about coverage than performance profiling, and has nothing to do with PGO.
- Is fundamentally limited by relying on counters auto-inserted by LLVM, with no knowledge of Rust beyond debuginfo.
jieyouxu added a commit to jieyouxu/rust that referenced this issue Nov 1, 2024
@jieyouxu
Rollup merge of rust-lang#131829 - Zalathar:goodbye-zprofile, r=cheny…
968e7aa 
…ukang

Remove support for `-Zprofile` (gcov-style coverage instrumentation)

Tracking issue: rust-lang#42524

MCP: rust-lang/compiler-team#798

---

This PR removes the unstable `-Zprofile` flag, which enables ”gcov-style” coverage instrumentation, along with its associated `-Zprofile-emit` configuration flag.

(The profile flag predates and is almost entirely separate from the stable `-Cinstrument-coverage` flag.)

Notably, the `-Zprofile` flag:
- Is largely untested in-tree, having only one run-make test that does not check whether its output is correct or useful.
- Has no known maintainer.
- Has seen no push towards stabilization.
- Has at least one severe regression reported in 2022 that apparently remains unaddressed.
  - rust-lang#100125
- Is confusingly named, since it appears to be more about coverage than performance profiling, and has nothing to do with PGO.
- Is fundamentally limited by relying on counters auto-inserted by LLVM, with no knowledge of Rust beyond debuginfo.
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this issue Nov 1, 2024
@GuillaumeGomez
Rollup merge of rust-lang#131829 - Zalathar:goodbye-zprofile, r=cheny…
526c67f 
…ukang

Remove support for `-Zprofile` (gcov-style coverage instrumentation)

Tracking issue: rust-lang#42524

MCP: rust-lang/compiler-team#798

---

This PR removes the unstable `-Zprofile` flag, which enables ”gcov-style” coverage instrumentation, along with its associated `-Zprofile-emit` configuration flag.

(The profile flag predates and is almost entirely separate from the stable `-Cinstrument-coverage` flag.)

Notably, the `-Zprofile` flag:
- Is largely untested in-tree, having only one run-make test that does not check whether its output is correct or useful.
- Has no known maintainer.
- Has seen no push towards stabilization.
- Has at least one severe regression reported in 2022 that apparently remains unaddressed.
  - rust-lang#100125
- Is confusingly named, since it appears to be more about coverage than performance profiling, and has nothing to do with PGO.
- Is fundamentally limited by relying on counters auto-inserted by LLVM, with no knowledge of Rust beyond debuginfo.
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Nov 2, 2024
@rust-timer
Unrolled build for rust-lang#131829
316805b 
Rollup merge of rust-lang#131829 - Zalathar:goodbye-zprofile, r=chenyukang

Remove support for `-Zprofile` (gcov-style coverage instrumentation)

Tracking issue: rust-lang#42524

MCP: rust-lang/compiler-team#798

---

This PR removes the unstable `-Zprofile` flag, which enables ”gcov-style” coverage instrumentation, along with its associated `-Zprofile-emit` configuration flag.

(The profile flag predates and is almost entirely separate from the stable `-Cinstrument-coverage` flag.)

Notably, the `-Zprofile` flag:
- Is largely untested in-tree, having only one run-make test that does not check whether its output is correct or useful.
- Has no known maintainer.
- Has seen no push towards stabilization.
- Has at least one severe regression reported in 2022 that apparently remains unaddressed.
  - rust-lang#100125
- Is confusingly named, since it appears to be more about coverage than performance profiling, and has nothing to do with PGO.
- Is fundamentally limited by relying on counters auto-inserted by LLVM, with no knowledge of Rust beyond debuginfo.
@Minoru Minoru mentioned this issue Nov 5, 2024
Closed
@josecelano josecelano mentioned this issue Nov 5, 2024
Closed
@Nichokas Nichokas mentioned this issue Apr 7, 2025
Open
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