Miri function identity hack: account for possible inlining

compiler/rustc_middle/src/mir/interpret/mod.rs

@@ -126,6 +126,7 @@ use std::num::NonZero;
 use std::sync::atomic::{AtomicU32, Ordering};
 
 use rustc_ast::LitKind;
+use rustc_attr::InlineAttr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::{HashMapExt, Lock};
 use rustc_data_structures::tiny_list::TinyList;
@@ -555,16 +556,21 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn reserve_and_set_fn_alloc(self, instance: Instance<'tcx>) -> AllocId {
         // Functions cannot be identified by pointers, as asm-equal functions can get deduplicated
         // by the linker (we set the "unnamed_addr" attribute for LLVM) and functions can be
-        // duplicated across crates.
-        // We thus generate a new `AllocId` for every mention of a function. This means that
-        // `main as fn() == main as fn()` is false, while `let x = main as fn(); x == x` is true.
-        // However, formatting code relies on function identity (see #58320), so we only do
-        // this for generic functions. Lifetime parameters are ignored.
+        // duplicated across crates. We thus generate a new `AllocId` for every mention of a
+        // function. This means that `main as fn() == main as fn()` is false, while `let x = main as
+        // fn(); x == x` is true. However, formatting code relies on function identity (see #58320)
+        // -- that's likely broken, but for now we have to support it to make Miri work. So we
+        // identify whether codegen will actually emit duplicate functions. It does that when they
+        // have non-lifetime generics, or when they can be inlined.
         let is_generic = instance
             .args
             .into_iter()
             .any(|kind| !matches!(kind.unpack(), GenericArgKind::Lifetime(_)));
-        if is_generic {
+        let can_be_inlined = match self.codegen_fn_attrs(instance.def_id()).inline {
+            InlineAttr::Never => false,
+            _ => true,
+        };
+        if is_generic || can_be_inlined {
             // Get a fresh ID.
             let mut alloc_map = self.alloc_map.lock();
             let id = alloc_map.reserve();