Closures inherit #[optimize] from the enclosing function by default.

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -1,7 +1,7 @@
 use rustc_abi::{Align, ExternAbi};
 use rustc_hir::attrs::{
     AttributeKind, EiiImplResolution, InlineAttr, InstrumentFnAttr as HirInstrumentFnAttr, Linkage,
-    RtsanSetting, UsedBy,
+    OptimizeAttr, RtsanSetting, UsedBy,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -354,6 +354,17 @@ fn apply_overrides(tcx: TyCtxt<'_>, did: LocalDefId, codegen_fn_attrs: &mut Code
         }
     }
 
+    // Closures inherit `#[optimize]` annotations.
+    if tcx.is_closure_like(did.to_def_id()) {
+        let owner_id = tcx.parent(did.to_def_id());
+        if tcx.def_kind(owner_id).has_codegen_attrs() {
+            let owner_attrs = tcx.codegen_fn_attrs(owner_id);
+            if codegen_fn_attrs.optimize == OptimizeAttr::Default {
+                codegen_fn_attrs.optimize = owner_attrs.optimize;
+            }
+        }
+    }
+
     // When `no_builtins` is applied at the crate level, we should add the
     // `no-builtins` attribute to each function to ensure it takes effect in LTO.
     let no_builtins = find_attr!(tcx, crate, NoBuiltins);

tests/codegen-llvm/optimize-closures-inheritance.rs

@@ -0,0 +1,33 @@
+//! Ensure that `#[optimize]` applied to an outer function is inherited by closures
+//! and their coercion shims.
+
+//@ compile-flags: -Copt-level=3
+
+#![feature(optimize_attribute)]
+#![crate_type = "lib"]
+
+// CHECK-DAG: define{{.*}}void {{.*}}test_none{{.*}}call_once{{.*}}#[[ATTR_NONE:[0-9]+]]
+// CHECK-DAG: define{{.*}}void {{.*}}test_none{{.*}}B{{[0-9]+}}_() {{.*}}#[[ATTR_NONE]]
+// CHECK-DAG: define{{.*}}void {{.*}}test_size{{.*}}call_once{{.*}}#[[ATTR_SIZE:[0-9]+]]
+
+// CHECK-DAG: attributes #[[ATTR_NONE]] = { {{.*}}noinline{{.*}}optnone{{.*}} }
+// CHECK-DAG: attributes #[[ATTR_SIZE]] = { {{.*}}optsize{{.*}} }
+
+extern "C" {
+    fn side_effect_1();
+    fn side_effect_2();
+}
+
+#[optimize(none)]
+#[no_mangle]
+pub fn test_none() -> fn() {
+    let closure = || unsafe { side_effect_1() };
+    closure
+}
+
+#[optimize(size)]
+#[no_mangle]
+pub fn test_size() -> fn() {
+    let closure = || unsafe { side_effect_2() };
+    closure
+}