[Bug c/109828] New: C2x:static compound literal (with flexible array) in initializer leads to invalid size and ICE

["yann at droneaud dot fr" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109828

            Bug ID: 109828
           Summary: C2x:static compound literal (with flexible array) in
                    initializer leads to invalid size and ICE
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yann at droneaud dot fr
  Target Milestone: ---

The following code is badly compiled by GCC 13.1:

    struct s { int i; char c[]; };

    const struct s s = { .c = "0", };
    const struct s *r = &(constexpr struct s) { .c = "1", };
    const struct s *t = &(static struct s) { .c = "2", };

Targetting x86-64 / amd64, compiling this with gcc -std=gnu2x -S, produces
surprising large .zero directive:

    s: 
        .zero   4
        .string "0"
    __compound_literal.0:
        .zero   4
        .string "1"
        .zero   18446744073709551613
        .zero   1
    r:
        .quad   __compound_literal.0
    __compound_literal.1:
        .zero   4
        .string "2"
        .zero   18446744073709551613
        .zero   1
    t:
        .quad   __compound_literal.1


Adding a call to __builtin_object_size() and compiling with optimization
triggers an ICE

    size_t ice(void)
    {
        return __builtin_object_size(t, 0);
    }


    $ gcc -std=gnu2x -O2 -S ice.c
    ice.c: In function ‘ice’:
    ice.c:11:12: internal compiler error: Segmentation fault
       11 |     return __builtin_object_size(t, 0);
          |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~
    0xc4dc6f crash_signal
            ../../gcc/toplev.cc:317
    0x7f39935907cf ???
           
/usr/src/debug/glibc-2.37.9000-9.fc39.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c:0
    0xb1023e tree_fits_poly_int64_p(tree_node const*)
            ../../gcc/tree.cc:6378
    0xb1023e tree_to_poly_int64(tree_node const*)
            ../../gcc/tree.cc:3285
    0x83b5bb component_ref_size(tree_node*, special_array_member*)
            ../../gcc/tree.cc:13199
    0x8096ed decl_init_size(tree_node*, bool)
            ../../gcc/tree-object-size.cc:493
    0xc7f08b addr_object_size
            ../../gcc/tree-object-size.cc:568
    0x6d0248 fold_builtin_object_size
            ../../gcc/builtins.cc:10808
    0x6d0248 fold_builtin_2
            ../../gcc/builtins.cc:9841
    0x6d0248 fold_builtin_n(unsigned int, tree_node*, tree_node*, tree_node**,
int, bool) [clone .isra.0]
            ../../gcc/builtins.cc:9949
    0x12084a6 gimplify_call_expr
            ../../gcc/gimplify.cc:3824
    0x12084a6 gimplify_expr(tree_node**, gimple**, gimple**, bool
(*)(tree_node*), int)
            ../../gcc/gimplify.cc:16348
    0x1207508 gimplify_modify_expr
            ../../gcc/gimplify.cc:6153
    0x1207508 gimplify_expr(tree_node**, gimple**, gimple**, bool
(*)(tree_node*), int)
            ../../gcc/gimplify.cc:16376
    0x1206dfc gimplify_stmt(tree_node**, gimple**)
            ../../gcc/gimplify.cc:7219
    0x1699436 gimplify_and_add(tree_node*, gimple**)
            ../../gcc/gimplify.cc:492
    0x1699436 gimplify_return_expr
            ../../gcc/gimplify.cc:1680
    0x1208676 gimplify_expr(tree_node**, gimple**, gimple**, bool
(*)(tree_node*), int)
            ../../gcc/gimplify.cc:16638
    0x1206dfc gimplify_stmt(tree_node**, gimple**)
            ../../gcc/gimplify.cc:7219
    0x1698c04 gimplify_bind_expr
            ../../gcc/gimplify.cc:1430

See https://godbolt.org/z/fnnW5T8TG