Collect panic/panic_bounds_check during monomorphization

compiler/rustc_monomorphize/src/collector.rs

@@ -806,13 +806,22 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
                     }
                 }
             }
+            mir::TerminatorKind::Assert { ref msg, .. } => {
+                let lang_item = match msg {
+                    mir::AssertKind::BoundsCheck { .. } => LangItem::PanicBoundsCheck,
+                    _ => LangItem::Panic,
+                };
+                let instance = Instance::mono(tcx, tcx.require_lang_item(lang_item, Some(source)));
+                if should_codegen_locally(tcx, &instance) {
+                    self.output.push(create_fn_mono_item(tcx, instance, source));
+                }
+            }
             mir::TerminatorKind::Goto { .. }
             | mir::TerminatorKind::SwitchInt { .. }
             | mir::TerminatorKind::Resume
             | mir::TerminatorKind::Abort
             | mir::TerminatorKind::Return
-            | mir::TerminatorKind::Unreachable
+            | mir::TerminatorKind::Unreachable => {}
-            | mir::TerminatorKind::Assert { .. } => {}
             mir::TerminatorKind::GeneratorDrop
             | mir::TerminatorKind::Yield { .. }
             | mir::TerminatorKind::FalseEdge { .. }

src/test/codegen-units/item-collection/implicit-panic-call.rs

@@ -0,0 +1,58 @@
+// compile-flags:-Zprint-mono-items=lazy
+
+// rust-lang/rust#90405
+// Ensure implicit panic calls are collected
+
+#![feature(lang_items)]
+#![feature(no_core)]
+#![crate_type = "lib"]
+#![no_core]
+#![no_std]
+
+#[lang = "panic_location"]
+struct Location<'a> {
+    _file: &'a str,
+    _line: u32,
+    _col: u32,
+}
+
+#[lang = "panic"]
+#[inline]
+#[track_caller]
+fn panic(_: &'static str) -> ! {
+    loop {}
+}
+
+#[lang = "sized"]
+trait Sized {}
+
+#[lang = "copy"]
+trait Copy {}
+
+#[lang = "freeze"]
+trait Freeze {}
+
+impl Copy for i32 {}
+
+#[lang = "div"]
+trait Div<Rhs = Self> {
+    type Output;
+    fn div(self, rhs: Rhs) -> Self::Output;
+}
+
+impl Div for i32 {
+    type Output = i32;
+    fn div(self, rhs: i32) -> i32 {
+        self / rhs
+    }
+}
+
+#[allow(unconditional_panic)]
+pub fn foo() {
+    // This implicitly generates a panic call.
+    let _ = 1 / 0;
+}
+
+//~ MONO_ITEM fn foo
+//~ MONO_ITEM fn <i32 as Div>::div
+//~ MONO_ITEM fn panic