[Bug c/101266] ICE with -g: in loc_list_from_tree_1, at dwarf2out.c:19421

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101266

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|debug                       |c
     Ever confirmed|0                           |1
            Version|tree-ssa                    |12.0
   Last reconfirmed|                            |2021-06-30
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  We hit

#1  0x0000000000d898e5 in loc_list_from_tree_1 (loc=
    <compound_literal_expr 0x7ffff6688240>, want_address=0, context=0x0)
    at /home/rguenther/src/gcc2/gcc/dwarf2out.c:19421
19421           gcc_unreachable ();
(gdb) l
19416           }
19417
19418         /* Otherwise this is a generic code; we should just lists all of
19419            these explicitly.  We forgot one.  */
19420         if (flag_checking)
19421           gcc_unreachable ();
(gdb) p loc
$1 = <compound_literal_expr 0x7ffff6688240>
(gdb) p debug_generic_expr (loc)
<<< Unknown tree: compound_literal_expr
    int D.1943 = 1; >>>

and the original tree we ask for is

(long int) SAVE_EXPR <<<< Unknown tree: compound_literal_expr
    int D.1943 = 1; >>>> + -1

this looks like some missed DECL_EXPR / gimplification or a missed error.
clang complains:

> clang-9 t.c -S
t.c:1:9: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
typedef U;
~~~~~~~ ^
t.c:2:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
fn8(U (*)[(int){1}]) {}
^
t.c:2:9: error: parameter name omitted
fn8(U (*)[(int){1}]) {}
        ^
2 warnings and 1 error generated.

but adding a parameter name doesn't fix anything.  Note we call
dwarf2out_decl via

#14 0x0000000000d9f4f4 in dwarf2out_type_decl (
    decl=<type_decl 0x7ffff656b428>, local=0)
    at /home/rguenther/src/gcc2/gcc/dwarf2out.c:27099
#15 0x000000000120699d in rest_of_decl_compilation (
    decl=<type_decl 0x7ffff656b428>, top_level=1, at_end=0)
    at /home/rguenther/src/gcc2/gcc/passes.c:251
#16 0x0000000000a614a7 in finish_decl (decl=<type_decl 0x7ffff656b428>, 
    init_loc=246464, init=<tree 0x0>, origtype=<tree 0x0>, 
    asmspec_tree=<tree 0x0>) at /home/rguenther/src/gcc2/gcc/c/c-decl.c:5606
#17 0x0000000000a65c38 in grokdeclarator (declarator=0x385b320, 
    declspecs=0x385b170, decl_context=PARM, initialized=false, width=0x0, 
    decl_attrs=0x7fffffffd628, expr=0x7fffffffd648, 
    expr_const_operands=0x7fffffffd49f, deprecated_state=DEPRECATED_NORMAL)
    at /home/rguenther/src/gcc2/gcc/c/c-decl.c:7171

so this is before any gimplification happened.