Don't try to store func_addr for FnDef in trans_const_value

This would crash, because the place provides 0 bytes of space for FnDef

Author: bjorn3

src/base.rs

@@ -474,9 +474,17 @@ fn trans_stmt<'a, 'tcx: 'a>(
                     lval.write_cvalue(fx, CValue::ByVal(res, layout));
                 }
                 Rvalue::Cast(CastKind::ReifyFnPointer, operand, ty) => {
-                    let operand = trans_operand(fx, operand);
                     let layout = fx.layout_of(ty);
-                    lval.write_cvalue(fx, operand.unchecked_cast_to(layout));
+                    match fx.monomorphize(&operand.ty(&fx.mir.local_decls, fx.tcx)).sty {
+                        ty::FnDef(def_id, substs) => {
+                            let func_ref = fx.get_function_ref(
+                                Instance::resolve(fx.tcx, ParamEnv::reveal_all(), def_id, substs).unwrap(),
+                            );
+                            let func_addr = fx.bcx.ins().func_addr(fx.pointer_type, func_ref);
+                            lval.write_cvalue(fx, CValue::ByVal(func_addr, layout));
+                        }
+                        _ => bug!("Trying to ReifyFnPointer on non FnDef {:?}", ty),
+                    }
                 }
                 Rvalue::Cast(CastKind::UnsafeFnPointer, operand, ty) => {
                     let operand = trans_operand(fx, operand);

src/constant.rs

@@ -110,12 +110,11 @@ fn trans_const_value<'a, 'tcx: 'a>(
             let bits = const_.val.try_to_bits(layout.size).unwrap();
             CValue::const_val(fx, ty, bits as i128 as i64)
         }
-        ty::FnDef(def_id, substs) => {
-            let func_ref = fx.get_function_ref(
-                Instance::resolve(fx.tcx, ParamEnv::reveal_all(), def_id, substs).unwrap(),
-            );
-            let func_addr = fx.bcx.ins().func_addr(fx.pointer_type, func_ref);
-            CValue::ByVal(func_addr, layout)
+        ty::FnDef(_def_id, _substs) => {
+            CValue::ByRef(
+                fx.bcx.ins().iconst(fx.pointer_type, 0),
+                layout
+            )
         }
         _ => trans_const_place(fx, const_).to_cvalue(fx),
     }