Support generating unique profraw files by default when using -C instrument-coverage
#100381
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A-code-coverage
Area: Source-based code coverage (-Cinstrument-coverage)
C-enhancement
Category: An issue proposing an enhancement or a PR with one.
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Aug 16, 2022
…ut, r=wesleywiser Add support for generating unique profraw files by default when using `-C instrument-coverage` Currently, enabling the rustc flag `-C instrument-coverage` instruments the given crate and by default uses the naming scheme `default.profraw` for any instrumented profile files generated during the execution of a binary linked against this crate. This leads to multiple binaries being executed overwriting one another and causing only the last executable run to contain actual coverage results. This can be overridden by manually setting the environment variable `LLVM_PROFILE_FILE` to use a unique naming scheme. This PR adds a change to add support for a reasonable default for rustc to use when enabling coverage instrumentation similar to how the Rust compiler treats generating these same `profraw` files when PGO is enabled. The new naming scheme is set to `default_%m_%p.profraw` to ensure the uniqueness of each file being generated using [LLVMs special pattern strings](https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#running-the-instrumented-program). Today the compiler sets the default for PGO `profraw` files to `default_%m.profraw` to ensure a unique file for each run. The same can be done for the instrumented profile files generated via the `-C instrument-coverage` flag as well which LLVM has API support for. Linked Issue: rust-lang#100381 r? `@wesleywiser`
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Currently, when enabling the instrumentation of Rust crates using the
-C instrument-coveragerustc flag, rustc does not set any default naming scheme for the generated*.profrawfiles. Today, a user has two options:default.profraw. Thie issue here is if there is more than one binary being executed that is linked to the instrumented library, LLVM would overwrite the coverage results from the previous executed binary.LLVM_PROFILE_FILEenvironment variable and apply LLVMs special pattern strings to ensure unique files are generated.LLVM also has API support for passing in the designated filename for instrumented profile files via rustc. This is leveraged today when enabling profile guided optimization or PGO. The Rust compiler directly sets a default naming scheme for the generated profraw file,
default_%m.profraw.Profile files generated by rustc's
-C instrument-coverageshould have the same or similar defaults to ensure coverage results are not overwritten by each test binary executed. A similar but more unique version of the default for PGO instrumented profile files should be used since multiple binaries are executed using the same instrumented library such asdefault_%m_%p.profraw.The text was updated successfully, but these errors were encountered: