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Commit d13e851

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Zalathartshepang
authored andcommitted
Prominently mention profiler = true on the coverage page
Enabling the profiler runtime is an essential part of being able to properly work on the coverage instrumentation code. There's already a mention of it on this page, but it's made in passing and is easy to miss. This patch adds a much more prominent section containing recommended `config.toml` settings, including `profiler = true`.
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‎src/llvm-coverage-instrumentation.md‎

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@@ -34,6 +34,32 @@ Detailed instructions and examples are documented in the
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[coverage map]: https://llvm.org/docs/CoverageMappingFormat.html
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[rustc-book-instrument-coverage]: https://doc.rust-lang.org/nightly/rustc/instrument-coverage.html
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## Recommended `config.toml` settings
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When working on the coverage instrumentation code, it is usually necessary to
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**enable the profiler runtime** by setting `profiler = true` in `[build]`.
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This allows the compiler to produce instrumented binaries, and makes it possible
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to run the full coverage test suite.
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Enabling debug assertions in the compiler and in LLVM is recommended, but not
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mandatory.
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```toml
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# Similar to the "compiler" profile, but also enables debug assertions in LLVM.
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# These assertions can detect malformed coverage mappings in some cases.
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profile = "codegen"
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[build]
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# IMPORTANT: This tells the build system to build the LLVM profiler runtime.
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# Without it, the compiler can't produce coverage-instrumented binaries,
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# and many of the coverage tests will be skipped.
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profiler = true
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[rust]
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# Enable debug assertions in the compiler.
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debug-assertions = true
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```
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## Rust symbol mangling
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`-C instrument-coverage` automatically enables Rust symbol mangling `v0` (as
@@ -292,6 +318,10 @@ These tests compile and run a test program with coverage
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instrumentation, then use LLVM tools to convert the coverage data into a
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human-readable coverage report.
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> Tests in `coverage-run` mode have an implicit `// needs-profiler-support`
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> directive, so they will be skipped if the profiler runtime has not been
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> [enabled in `config.toml`](#recommended-configtoml-settings).
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Finally, the [`coverage-llvmir`] test compiles a simple Rust program
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with `-C instrument-coverage` and compares the compiled program's LLVM IR to
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expected LLVM IR instructions and structured data for a coverage-enabled

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