coverage: Detach #[coverage(..)] from codegen attribute handling

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -87,10 +87,7 @@ bitflags::bitflags! {
         /// #[cmse_nonsecure_entry]: with a TrustZone-M extension, declare a
         /// function as an entry function from Non-Secure code.
         const CMSE_NONSECURE_ENTRY      = 1 << 13;
-        /// `#[coverage(off)]`: indicates that the function should be ignored by
-        /// the MIR `InstrumentCoverage` pass and not added to the coverage map
-        /// during codegen.
-        const NO_COVERAGE               = 1 << 14;
+        // (Bit 14 was used for `#[coverage(off)]`, but is now unused.)
         /// `#[used(linker)]`:
         /// indicates that neither LLVM nor the linker will eliminate this function.
         const USED_LINKER               = 1 << 15;

compiler/rustc_middle/src/query/mod.rs

@@ -572,6 +572,14 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// Checks for `#[coverage(off)]` or `#[coverage(on)]`.
+    ///
+    /// Returns `false` if `#[coverage(off)]` was found, or `true` if
+    /// either `#[coverage(on)]` or no coverage attribute was found.
+    query coverage_attr_on(key: LocalDefId) -> bool {
+        desc { |tcx| "checking for `#[coverage(..)]` on `{}`", tcx.def_path_str(key) }
+    }
+
     /// Summarizes coverage IDs inserted by the `InstrumentCoverage` MIR pass
     /// (for compiler option `-Cinstrument-coverage`), after MIR optimizations
     /// have had a chance to potentially remove some of them.