> Am 21.11.2025 um 07:33 schrieb Jakub Jelinek <[email protected]>:
>
> Hi!
>
> In r16-4212 I had to tweak two spots in the gimplifier to ignore
> gotos jumping to labels with the new VACUOUS_INIT_LABEL_P flag
> (set by C++ FE when implementing goto/case interceptors with
> extra .DEFERRED_INIT calls, so that jumps over vacuous initialization
> are handled properly with the C++26 erroneous behavior requirements).
> Except as the following testcase shows, the checks blindly assumed
> that gimple_goto_dest operand is a LABEL_DECL, which is not the case
> for computed jumps.
>
> The following patch checks that gimple_goto_dest argument is a LABEL_DECL
> before testing VACUOUS_INIT_LABEL_P flag on it.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok
Richard
> 2025-11-20 Jakub Jelinek <[email protected]>
>
> PR middle-end/122773
> * gimplify.cc (collect_fallthrough_labels): Check whether
> gimple_goto_dest is a LABEL_DECL before testing VACUOUS_INIT_LABEL_P.
> (expand_FALLTHROUGH_r): Likewise.
>
> * gcc.dg/pr122773.c: New test.
>
> --- gcc/gimplify.cc.jj 2025-10-04 09:49:59.846567597 +0200
> +++ gcc/gimplify.cc 2025-11-20 16:21:49.291305638 +0100
> @@ -2673,6 +2673,7 @@ collect_fallthrough_labels (gimple_stmt_
> gsi_next (gsi_p);
> }
>
> + tree lab;
> /* Remember the last statement. Skip labels that are of no interest
> to us. */
> if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_LABEL)
> @@ -2691,7 +2692,9 @@ collect_fallthrough_labels (gimple_stmt_
> ;
> else if (flag_auto_var_init > AUTO_INIT_UNINITIALIZED
> && gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_GOTO
> - && VACUOUS_INIT_LABEL_P (gimple_goto_dest (gsi_stmt (*gsi_p))))
> + && (lab = gimple_goto_dest (gsi_stmt (*gsi_p)))
> + && TREE_CODE (lab) == LABEL_DECL
> + && VACUOUS_INIT_LABEL_P (lab))
> ;
> else if (!is_gimple_debug (gsi_stmt (*gsi_p)))
> prev = gsi_stmt (*gsi_p);
> @@ -2928,9 +2931,12 @@ expand_FALLTHROUGH_r (gimple_stmt_iterat
>
> gimple_stmt_iterator gsi2 = *gsi_p;
> stmt = gsi_stmt (gsi2);
> + tree lab;
> if (flag_auto_var_init > AUTO_INIT_UNINITIALIZED
> && gimple_code (stmt) == GIMPLE_GOTO
> - && VACUOUS_INIT_LABEL_P (gimple_goto_dest (stmt)))
> + && (lab = gimple_goto_dest (stmt))
> + && TREE_CODE (lab) == LABEL_DECL
> + && VACUOUS_INIT_LABEL_P (lab))
> {
> /* Handle for C++ artificial -ftrivial-auto-var-init=
> sequences. Those look like:
> --- gcc/testsuite/gcc.dg/pr122773.c.jj 2025-11-20 16:35:41.001856729 +0100
> +++ gcc/testsuite/gcc.dg/pr122773.c 2025-11-20 16:35:03.690369236 +0100
> @@ -0,0 +1,25 @@
> +/* PR middle-end/122773 */
> +/* { dg-do compile } */
> +/* { dg-options "-Wimplicit-fallthrough -O2 -ftrivial-auto-var-init=zero" }
> */
> +
> +void *l;
> +int
> +foo (int x)
> +{
> + __label__ l1, l2, l3;
> + static void *l[] = { &&l1, &&l2, &&l3 };
> + switch (0)
> + {
> + case 0:
> + while (0)
> + ;
> + goto *l[x];
> + }
> + l1:
> + ++x;
> + l2:
> + ++x;
> + l3:
> + ++x;
> + return x;
> +}
>
> Jakub
>
