On Thu, Jan 19, 2023 at 12:13 PM Jakub Jelinek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi!
>
> For anonymous union members we create artificial VAR_DECLs which
> have DECL_VALUE_EXPR for the actual COMPONENT_REF. That works
> just fine inside of functions (including global dynamic constructors),
> because during gimplification such VAR_DECLs are gimplified as
> their DECL_VALUE_EXPR. This is also done during regimplification.
>
> But references to these artificial vars in DECL_INITIAL expressions
> aren't ever replaced by the DECL_VALUE_EXPRs, so we end up either
> with link failures like on the testcase below, or worse ICEs with
> LTO.
>
> The following patch fixes those during cp_fully_fold_init where we
> already walk all the trees (!data->genericize means that
> function rather than cp_fold_function).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
I noticed (static) structured bindings has a similar issue but is not
fixed by this because this checks to see if it is an anonymous union
decl.
I filed PR 108474 for that.
Thanks,
Andrew Pinski
>
> 2023-01-19 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/53932
> * cp-gimplify.cc (cp_fold_r): During cp_fully_fold_init replace
> DECL_ANON_UNION_VAR_P VAR_DECLs with their corresponding
> DECL_VALUE_EXPR.
>
> * g++.dg/init/pr53932.C: New test.
>
> --- gcc/cp/cp-gimplify.cc.jj 2023-01-16 11:52:16.065734330 +0100
> +++ gcc/cp/cp-gimplify.cc 2023-01-19 18:13:54.592661735 +0100
> @@ -1010,6 +1010,16 @@ cp_fold_r (tree *stmt_p, int *walk_subtr
> }
> break;
>
> + case VAR_DECL:
> + /* In initializers replace anon union artificial VAR_DECLs
> + with their DECL_VALUE_EXPRs, as nothing will do it later. */
> + if (DECL_ANON_UNION_VAR_P (stmt) && !data->genericize)
> + {
> + *stmt_p = stmt = unshare_expr (DECL_VALUE_EXPR (stmt));
> + break;
> + }
> + break;
> +
> default:
> break;
> }
> --- gcc/testsuite/g++.dg/init/pr53932.C.jj 2023-01-19 18:22:24.837231192
> +0100
> +++ gcc/testsuite/g++.dg/init/pr53932.C 2023-01-19 18:20:51.776586408 +0100
> @@ -0,0 +1,25 @@
> +// PR c++/53932
> +// { dg-do link }
> +
> +static union { int i; };
> +int &r = i;
> +int s = i;
> +int *t = &i;
> +
> +void
> +foo (int **p, int *q)
> +{
> + static int &u = i;
> + static int v = i;
> + static int *w = &i;
> + int &x = i;
> + int y = i;
> + int *z = &i;
> + *p = &i;
> + *q = i;
> +}
> +
> +int
> +main ()
> +{
> +}
>
> Jakub
>
