reachability: skip instance without body; only collect Item instance

********* "demo" [Rlib] has reached 8 instances *********
"test" ("src/lib.rs:12:1: 12:26")
 => "#[Safety::inner(UnReachable, kind = \"precond\", memo =\n\"It's undefined behavior to reach code marked with this intrinsic function.\")]\n"

"MyStruct::get" ("src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(Init(self.ptr, u8, self.len), kind = \"precond\", memo =\n\"The ptr must be initialized first!\")]\n"

"MyStruct::get" ("src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(InBound(self.ptr, u8, self.len), kind = \"precond\", memo =\n\"The ptr must be within the length.\")]\n"

"MyStruct::get" ("src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(ValidNum(self.len * sizeof(u8), [0, isize :: MAX]), kind =\n\"precond\", memo =\n\"Slice length can't exceed isize::MAX due to allocation limit.\")]\n"

"MyStruct::get" ("src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(Alias(self.ptr), kind = \"hazard\", memo =\n\"Make sure don't alias the ptr.\")]\n"

********* "demo" [Executable] has reached 18 instances *********
"demo::MyStruct::get" ("/home/gh-zjp-CN/tag-std/demo/rustc_driver/tests/basic/src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(Init(self.ptr, u8, self.len), kind = \"precond\", memo =\n\"The ptr must be initialized first!\")]\n"

"demo::MyStruct::get" ("/home/gh-zjp-CN/tag-std/demo/rustc_driver/tests/basic/src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(InBound(self.ptr, u8, self.len), kind = \"precond\", memo =\n\"The ptr must be within the length.\")]\n"

"demo::MyStruct::get" ("/home/gh-zjp-CN/tag-std/demo/rustc_driver/tests/basic/src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(ValidNum(self.len * sizeof(u8), [0, isize :: MAX]), kind =\n\"precond\", memo =\n\"Slice length can't exceed isize::MAX due to allocation limit.\")]\n"

"demo::MyStruct::get" ("/home/gh-zjp-CN/tag-std/demo/rustc_driver/tests/basic/src/lib.rs:40:5: 40:42")
 => "#[Safety::inner(Alias(self.ptr), kind = \"hazard\", memo =\n\"Make sure don't alias the ptr.\")]\n"

Author: zjp-CN

demo/rustc_driver/src/main.rs

@@ -15,7 +15,11 @@ use rustc_hir::Attribute;
 use rustc_middle::ty::TyCtxt;
 use stable_mir::{
     CrateDef, ItemKind,
-    mir::{MirVisitor, mono::Instance, visit::Location},
+    mir::{
+        MirVisitor,
+        mono::{Instance, InstanceKind},
+        visit::Location,
+    },
     rustc_internal::internal,
     ty::Ty,
 };
@@ -62,7 +66,10 @@ struct Reachability {
 
 impl Reachability {
     fn add_instance(&mut self, instance: Instance) {
-        if self.instances.insert(instance) {
+        if self.instances.insert(instance)
+            && instance.has_body()
+            && matches!(instance.kind, InstanceKind::Item)
+        {
             // recurse if this is the first time of insertion
             if let Some(body) = instance.body() {
                 self.visit_body(&body);
@@ -92,7 +99,7 @@ fn print_tag_std_attrs_through_internal_apis(tcx: TyCtxt<'_>, instance: &Instanc
     });
     for attr in tool_attrs {
         println!(
-            "{fn_name:?} ({span:?}) => {attr:?}\n",
+            "{fn_name:?} ({span:?})\n => {attr:?}\n",
             fn_name = instance.name(),
             span = instance.def.span().diagnostic(),
             attr = rustc_hir_pretty::attribute_to_string(&tcx, attr)