Don't create data object for zero sized allocations

Author: bjorn3

src/constant.rs

@@ -137,18 +137,23 @@ pub(crate) fn codegen_const_value<'tcx>(
                 let alloc_id = prov.alloc_id();
                 let base_addr = match fx.tcx.global_alloc(alloc_id) {
                     GlobalAlloc::Memory(alloc) => {
-                        let data_id = data_id_for_alloc_id(
-                            &mut fx.constants_cx,
-                            fx.module,
-                            alloc_id,
-                            alloc.inner().mutability,
-                        );
-                        let local_data_id =
-                            fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
-                        if fx.clif_comments.enabled() {
-                            fx.add_comment(local_data_id, format!("{:?}", alloc_id));
+                        if alloc.inner().len() == 0 {
+                            assert_eq!(offset, Size::ZERO);
+                            fx.bcx.ins().iconst(fx.pointer_type, alloc.inner().align.bytes() as i64)
+                        } else {
+                            let data_id = data_id_for_alloc_id(
+                                &mut fx.constants_cx,
+                                fx.module,
+                                alloc_id,
+                                alloc.inner().mutability,
+                            );
+                            let local_data_id =
+                                fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
+                            if fx.clif_comments.enabled() {
+                                fx.add_comment(local_data_id, format!("{:?}", alloc_id));
+                            }
+                            fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
                         }
-                        fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
                     }
                     GlobalAlloc::Function(instance) => {
                         let func_id = crate::abi::import_function(fx.tcx, fx.module, instance);