418ae3e9a0
coverage: Skip instrumenting a function if no spans were extracted from MIR The immediate symptoms of #118643 were fixed by #118666, but some users reported that their builds now encounter another coverage-related ICE: ``` error: internal compiler error: compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs:98:17: A used function should have had coverage mapping data but did not: (...) ``` I was able to reproduce at least one cause of this error: if no relevant spans could be extracted from a function, but the function contains `CoverageKind::SpanMarker` statements, then codegen still thinks the function is instrumented and complains about the fact that it has no coverage spans. This PR prevents that from happening in two ways: - If we didn't extract any relevant spans from MIR, skip instrumenting the entire function and don't create a `FunctionCoverateInfo` for it. - If coverage codegen sees a `CoverageKind::SpanMarker` statement, skip it early and avoid creating `func_coverage`. --- Fixes #118850.
The codegen crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.