Don't auto-inline const functions

src/librustc/ty/instance.rs

@@ -173,10 +173,7 @@ impl<'tcx> InstanceDef<'tcx> {
             // available to normal end-users.
             return true
         }
-        let codegen_fn_attrs = tcx.codegen_fn_attrs(self.def_id());
-        // need to use `is_const_fn_raw` since we don't really care if the user can use it as a
-        // const fn, just whether the function should be inlined
-        codegen_fn_attrs.requests_inline() || tcx.is_const_fn_raw(self.def_id())
+        tcx.codegen_fn_attrs(self.def_id()).requests_inline()
     }
 }
 

src/librustc_mir/monomorphize/collector.rs

@@ -178,10 +178,6 @@
 //! Some things are not yet fully implemented in the current version of this
 //! module.
 //!
-//! ### Initializers of Constants and Statics
-//! Since no MIR is constructed yet for initializer expressions of constants and
-//! statics we cannot inspect these properly.
-//!
 //! ### Const Fns
 //! Ideally, no mono item should be generated for const fns unless there
 //! is a call to them that cannot be evaluated at compile time. At the moment
@@ -191,7 +187,6 @@
 use rustc::hir::{self, CodegenFnAttrFlags};
 use rustc::hir::itemlikevisit::ItemLikeVisitor;
 
-use rustc::hir::Node;
 use rustc::hir::def_id::DefId;
 use rustc::mir::interpret::{AllocId, ConstValue};
 use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
@@ -741,27 +736,27 @@ fn should_monomorphize_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance:
         ty::InstanceDef::CloneShim(..) => return true
     };
 
-    return match tcx.hir.get_if_local(def_id) {
-        Some(Node::ForeignItem(..)) => {
-            false // foreign items are linked against, not codegened.
-        }
-        Some(_) => true,
-        None => {
-            if tcx.is_reachable_non_generic(def_id) ||
-                tcx.is_foreign_item(def_id) ||
-                is_available_upstream_generic(tcx, def_id, instance.substs)
-            {
-                // We can link to the item in question, no instance needed
-                // in this crate
-                false
-            } else {
-                if !tcx.is_mir_available(def_id) {
-                    bug!("Cannot create local mono-item for {:?}", def_id)
-                }
-                true
-            }
-        }
-    };
+    if tcx.is_foreign_item(def_id) {
+        // We can always link to foreign items
+        return false;
+    }
+
+    if def_id.is_local() {
+        // local items cannot be referred to locally without monomorphizing them locally
+        return true;
+    }
+
+    if tcx.is_reachable_non_generic(def_id) ||
+       is_available_upstream_generic(tcx, def_id, instance.substs) {
+        // We can link to the item in question, no instance needed
+        // in this crate
+        return false;
+    }
+
+    if !tcx.is_mir_available(def_id) {
+        bug!("Cannot create local mono-item for {:?}", def_id)
+    }
+    return true;
 
     fn is_available_upstream_generic<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                def_id: DefId,

src/test/codegen-units/item-collection/unreferenced-const-fn.rs

@@ -11,11 +11,10 @@
 // ignore-tidy-linelength
 // compile-flags:-Zprint-mono-items=lazy
 
-// NB: We do not expect *any* monomorphization to be generated here.
-
 #![deny(dead_code)]
 #![crate_type = "rlib"]
 
+//~ MONO_ITEM fn unreferenced_const_fn::foo[0] @@ unreferenced_const_fn-cgu.0[External]
 pub const fn foo(x: u32) -> u32 {
     x + 0xf00
 }

src/test/ui/consts/auxiliary/const_fn_lib.rs

@@ -10,6 +10,24 @@
 
 // Crate that exports a const fn. Used for testing cross-crate.
 
+#![feature(const_fn)]
 #![crate_type="rlib"]
 
-pub const fn foo() -> usize { 22 } //~ ERROR const fn is unstable
+pub const fn foo() -> usize { 22 }
+
+pub const fn bar() -> fn() {
+    fn x() {}
+    x
+}
+
+#[inline]
+pub const fn bar_inlined() -> fn() {
+    fn x() {}
+    x
+}
+
+#[inline(always)]
+pub const fn bar_inlined_always() -> fn() {
+    fn x() {}
+    x
+}

src/test/ui/consts/const_fn_return_nested_fn_ptr.rs

@@ -0,0 +1,10 @@
+// compile-pass
+// aux-build:const_fn_lib.rs
+
+extern crate const_fn_lib;
+
+fn main() {
+    const_fn_lib::bar()();
+    const_fn_lib::bar_inlined()();
+    const_fn_lib::bar_inlined_always()();
+}