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? 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
