Rollup merge of #84875 - richkadel:no-coverage-dont-check-unused, r=tmandry

Removes unneeded check of `#[no_coverage]` in mapgen

There is an anticipated feature request to support a compiler flag that
only adds coverage for specific files (or perhaps mods). As I thought
about where that change would need to be supported, I realized that
checking the attribute in mapgen (for unused functions) was unnecessary.
The unused functions are only synthesized if they have MIR coverage, and
functions with the `no_coverage` attribute will not have been
instrumented with MIR coverage statements in the first place.

New tests confirm this.

Also, while adding tests, I updated resolved comments and FIXMEs in
other tests, and expanded comments and tests on one remaining issue that
is still not resolved.

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

1 files changed, 2 insertions, 6 deletions

diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index d19fda50bf6..30f125ca3be 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -8,7 +8,6 @@ use rustc_codegen_ssa::traits::{ConstMethods, CoverageInfoMethods};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_hir::def_id::{DefId, DefIdSet, LOCAL_CRATE};
 use rustc_llvm::RustString;
-use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::coverage::CodeRegion;
 use rustc_span::Symbol;
 
@@ -281,11 +280,8 @@ fn add_unused_functions<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
 
     let mut unused_def_ids_by_file: FxHashMap<Symbol, Vec<DefId>> = FxHashMap::default();
     for &non_codegenned_def_id in all_def_ids.difference(codegenned_def_ids) {
-        let codegen_fn_attrs = tcx.codegen_fn_attrs(non_codegenned_def_id);
-        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_COVERAGE) {
-            continue;
-        }
-        // Make sure the non-codegenned (unused) function has a file_name
+        // Make sure the non-codegenned (unused) function has at least one MIR
+        // `Coverage` statement with a code region, and return its file name.
         if let Some(non_codegenned_file_name) = tcx.covered_file_name(non_codegenned_def_id) {
             let def_ids =
                 unused_def_ids_by_file.entry(*non_codegenned_file_name).or_insert_with(Vec::new);