Rollup merge of #131829 - Zalathar:goodbye-zprofile, r=chenyukang

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

Tracking issue: #42524

MCP: https://github.com/rust-lang/compiler-team/issues/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.
  - #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.

2 files changed, 2 insertions, 33 deletions

diff --git a/src/doc/rustc/src/instrument-coverage.md b/src/doc/rustc/src/instrument-coverage.md
index ed091d8fc57..41da47e9206 100644
--- a/src/doc/rustc/src/instrument-coverage.md
+++ b/src/doc/rustc/src/instrument-coverage.md
@@ -2,12 +2,8 @@
 
 ## Introduction
 
-The Rust compiler includes two code coverage implementations:
-
--   A GCC-compatible, gcov-based coverage implementation, enabled with `-Z profile`, which derives coverage data based on DebugInfo.
--   A source-based code coverage implementation, enabled with `-C instrument-coverage`, which uses LLVM's native, efficient coverage instrumentation to generate very precise coverage data.
-
-This document describes how to enable and use the LLVM instrumentation-based coverage, via the `-C instrument-coverage` compiler flag.
+This document describes how to enable and use LLVM instrumentation-based coverage,
+via the `-C instrument-coverage` compiler flag.
 
 ## How it works
 
diff --git a/src/doc/unstable-book/src/compiler-flags/profile.md b/src/doc/unstable-book/src/compiler-flags/profile.md
deleted file mode 100644
index 71303bfaff2..00000000000
--- a/src/doc/unstable-book/src/compiler-flags/profile.md
+++ /dev/null
@@ -1,27 +0,0 @@
-# `profile`
-
-The tracking issue for this feature is: [#42524](https://github.com/rust-lang/rust/issues/42524).
-
-------------------------
-
-This feature allows the generation of code coverage reports.
-
-Set the `-Zprofile` compiler flag in order to enable gcov profiling.
-
-For example:
-```Bash
-cargo new testgcov --bin
-cd testgcov
-export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
-export CARGO_INCREMENTAL=0
-cargo build
-cargo run
-```
-
-Once you've built and run your program, files with the `gcno` (after build) and `gcda` (after execution) extensions will be created.
-You can parse them with [llvm-cov gcov](https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-gcov) or [grcov](https://github.com/mozilla/grcov).
-
-Please note that `RUSTFLAGS` by default applies to everything that cargo builds and runs during a build!
-When the `--target` flag is explicitly passed to cargo, the `RUSTFLAGS` no longer apply to build scripts and procedural macros.
-For more fine-grained control consider passing a `RUSTC_WRAPPER` program to cargo that only adds the profiling flags to
-rustc for the specific crates you want to profile.