From 15cccb97d60a19fc7120bb57840a83bdcc90dbad Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 3 Jun 2022 15:21:57 -0700
Subject: [PATCH] Encode MIR for 'unreachable' non-generic fns

---
 compiler/rustc_passes/src/reachable.rs        | 33 ++++-----------
 .../ui/codegen/auxiliary/issue-97708-aux.rs   | 41 +++++++++++++++++++
 src/test/ui/codegen/issue-97708.rs            |  9 ++++
 3 files changed, 58 insertions(+), 25 deletions(-)
 create mode 100644 src/test/ui/codegen/auxiliary/issue-97708-aux.rs
 create mode 100644 src/test/ui/codegen/issue-97708.rs

diff --git a/compiler/rustc_passes/src/reachable.rs b/compiler/rustc_passes/src/reachable.rs
index 0ded6a421f57f..75376cdc592d3 100644
--- a/compiler/rustc_passes/src/reachable.rs
+++ b/compiler/rustc_passes/src/reachable.rs
@@ -148,32 +148,15 @@ impl<'tcx> ReachableContext<'tcx> {
                 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
                 | hir::TraitItemKind::Type(..) => false,
             },
-            Some(Node::ImplItem(impl_item)) => {
-                match impl_item.kind {
-                    hir::ImplItemKind::Const(..) => true,
-                    hir::ImplItemKind::Fn(..) => {
-                        let attrs = self.tcx.codegen_fn_attrs(def_id);
-                        let generics = self.tcx.generics_of(def_id);
-                        if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
-                            true
-                        } else {
-                            let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
-                            let impl_did = self.tcx.hir().get_parent_item(hir_id);
-                            // Check the impl. If the generics on the self
-                            // type of the impl require inlining, this method
-                            // does too.
-                            match self.tcx.hir().expect_item(impl_did).kind {
-                                hir::ItemKind::Impl { .. } => {
-                                    let generics = self.tcx.generics_of(impl_did);
-                                    generics.requires_monomorphization(self.tcx)
-                                }
-                                _ => false,
-                            }
-                        }
-                    }
-                    hir::ImplItemKind::TyAlias(_) => false,
+            Some(Node::ImplItem(impl_item)) => match impl_item.kind {
+                hir::ImplItemKind::Const(..) => true,
+                hir::ImplItemKind::Fn(..) => {
+                    let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
+                    let impl_did = self.tcx.hir().get_parent_item(hir_id);
+                    method_might_be_inlined(self.tcx, impl_item, impl_did)
                 }
-            }
+                hir::ImplItemKind::TyAlias(_) => false,
+            },
             Some(_) => false,
             None => false, // This will happen for default methods.
         }
diff --git a/src/test/ui/codegen/auxiliary/issue-97708-aux.rs b/src/test/ui/codegen/auxiliary/issue-97708-aux.rs
new file mode 100644
index 0000000000000..e296bd3911310
--- /dev/null
+++ b/src/test/ui/codegen/auxiliary/issue-97708-aux.rs
@@ -0,0 +1,41 @@
+use std::{ptr::NonNull, task::Poll};
+
+struct TaskRef;
+
+struct Header {
+    vtable: &'static Vtable,
+}
+
+struct Vtable {
+    poll: unsafe fn(TaskRef) -> Poll<()>,
+    deallocate: unsafe fn(NonNull<Header>),
+}
+
+// in the "Header" type, which is a private type in maitake
+impl Header {
+    pub(crate) const fn new_stub() -> Self {
+        unsafe fn nop(_ptr: TaskRef) -> Poll<()> {
+            Poll::Pending
+        }
+
+        unsafe fn nop_deallocate(ptr: NonNull<Header>) {
+            unreachable!("stub task ({ptr:p}) should never be deallocated!");
+        }
+
+        Self { vtable: &Vtable { poll: nop, deallocate: nop_deallocate } }
+    }
+}
+
+// This is a public type in `maitake`
+#[repr(transparent)]
+#[cfg_attr(loom, allow(dead_code))]
+pub struct TaskStub {
+    hdr: Header,
+}
+
+impl TaskStub {
+    /// Create a new unique stub [`Task`].
+    pub const fn new() -> Self {
+        Self { hdr: Header::new_stub() }
+    }
+}
diff --git a/src/test/ui/codegen/issue-97708.rs b/src/test/ui/codegen/issue-97708.rs
new file mode 100644
index 0000000000000..8cb28e9f1f661
--- /dev/null
+++ b/src/test/ui/codegen/issue-97708.rs
@@ -0,0 +1,9 @@
+// build-pass
+// aux-build:issue-97708-aux.rs
+
+extern crate issue_97708_aux;
+use issue_97708_aux::TaskStub;
+
+static TASK_STUB: TaskStub = TaskStub::new();
+
+fn main() {}