Rollup merge of rust-lang#84815 - richkadel:coverage-docs-update-2021-05, r=tmandry

Update coverage docs and command line help

r? `@tmandry`
cc: `@wesleywiser`

Author: JohnTitor

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -249,7 +249,7 @@ fn save_function_record(
 ///
 /// We can find the unused functions (including generic functions) by the set difference of all MIR
 /// `DefId`s (`tcx` query `mir_keys`) minus the codegenned `DefId`s (`tcx` query
-/// `collect_and_partition_mono_items`).
+/// `codegened_and_inlined_items`).
 ///
 /// *HOWEVER* the codegenned `DefId`s are partitioned across multiple `CodegenUnit`s (CGUs), and
 /// this function is processing a `function_coverage_map` for the functions (`Instance`/`DefId`)

compiler/rustc_session/src/options.rs

@@ -1080,12 +1080,12 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "gather statistics about the input (default: no)"),
     instrument_coverage: Option<InstrumentCoverage> = (None, parse_instrument_coverage, [TRACKED],
         "instrument the generated code to support LLVM source-based code coverage \
-        reports (note, the compiler build config must include `profiler = true`, \
-        and is mutually exclusive with `-C profile-generate`/`-C profile-use`); \
-        implies `-Z symbol-mangling-version=v0`; disables/overrides some Rust \
-        optimizations. Optional values are: `=all` (default coverage), \
-        `=except-unused-generics`, `=except-unused-functions`, or `=off` \
-        (default: instrument-coverage=off)"),
+        reports (note, the compiler build config must include `profiler = true`); \
+        implies `-Z symbol-mangling-version=v0`. Optional values are:
+        `=all` (implicit value)
+        `=except-unused-generics`
+        `=except-unused-functions`
+        `=off` (default)"),
     instrument_mcount: bool = (false, parse_bool, [TRACKED],
         "insert function instrument code for mcount-based tracing (default: no)"),
     keep_hygiene_data: bool = (false, parse_bool, [UNTRACKED],