gave unused_fn WeakAnyLinkage; moved create_pgo_func_name_var

The sample json5format tests produce coverage results again (and work
with opt-level 3!)

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -67,25 +67,12 @@ impl CoverageInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             let mut pgo_func_name_var_map = coverage_context.pgo_func_name_var_map.borrow_mut();
             pgo_func_name_var_map
                 .entry(instance)
-                .or_insert_with(|| self.create_pgo_func_name_var(instance))
+                .or_insert_with(|| create_pgo_func_name_var(self, instance))
         } else {
             bug!("Could not get the `coverage_context`");
         }
     }
 
-    /// Calls llvm::createPGOFuncNameVar() with the given function instance's
-    /// mangled function name. The LLVM API returns an llvm::GlobalVariable
-    /// containing the function name, with the specific variable name and
-    /// linkage required by LLVM InstrProf source-based coverage
-    /// instrumentation. Use `bx.get_pgo_func_name_var()` to ensure the variable
-    /// is only created once per `Instance`.
-    fn create_pgo_func_name_var(&self, instance: Instance<'tcx>) -> &'ll llvm::Value {
-        let mangled_fn_name = CString::new(self.tcx.symbol_name(instance).name)
-            .expect("error converting function name to C string");
-        let llfn = self.get_fn(instance);
-        unsafe { llvm::LLVMRustCoverageCreatePGOFuncNameVar(llfn, mangled_fn_name.as_ptr()) }
-    }
-
     fn define_unused_fn(&self, def_id: DefId) {
         let instance = declare_unused_fn(self, &def_id);
         codegen_unused_fn_and_counter(self, instance);
@@ -210,10 +197,8 @@ fn declare_unused_fn(cx: &CodegenCx<'ll, 'tcx>, def_id: &DefId) -> Instance<'tcx
         ),
     );
 
-    unsafe {
+    llvm::set_linkage(llfn, llvm::Linkage::WeakAnyLinkage);
-        llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
+    llvm::set_visibility(llfn, llvm::Visibility::Hidden);
-        llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
-    }
 
     cx.instances.borrow_mut().insert(instance, llfn);
 
@@ -261,6 +246,22 @@ fn add_function_coverage(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>, de
     }
 }
 
+/// Calls llvm::createPGOFuncNameVar() with the given function instance's
+/// mangled function name. The LLVM API returns an llvm::GlobalVariable
+/// containing the function name, with the specific variable name and linkage
+/// required by LLVM InstrProf source-based coverage instrumentation. Use
+/// `bx.get_pgo_func_name_var()` to ensure the variable is only created once per
+/// `Instance`.
+fn create_pgo_func_name_var(
+    cx: &CodegenCx<'ll, 'tcx>,
+    instance: Instance<'tcx>,
+) -> &'ll llvm::Value {
+    let mangled_fn_name = CString::new(cx.tcx.symbol_name(instance).name)
+        .expect("error converting function name to C string");
+    let llfn = cx.get_fn(instance);
+    unsafe { llvm::LLVMRustCoverageCreatePGOFuncNameVar(llfn, mangled_fn_name.as_ptr()) }
+}
+
 pub(crate) fn write_filenames_section_to_buffer<'a>(
     filenames: impl IntoIterator<Item = &'a CString>,
     buffer: &RustString,

compiler/rustc_codegen_ssa/src/traits/coverageinfo.rs

@@ -29,10 +29,6 @@ pub trait CoverageInfoMethods<'tcx>: BackendTypes {
     /// `instrprof.increment()`. The `Value` is only created once per instance.
     /// Multiple invocations with the same instance return the same `Value`.
     fn get_pgo_func_name_var(&self, instance: Instance<'tcx>) -> Self::Value;
-
-    /// Creates a new PGO function name variable. This should only be called
-    /// to fill in the unused function names array.
-    fn create_pgo_func_name_var(&self, instance: Instance<'tcx>) -> Self::Value;
 }
 
 pub trait CoverageInfoBuilderMethods<'tcx>: BackendTypes {