[Bug lto/54898] [4.8 regression] ICE in uniquify_nodes, at lto/lto.c:1898

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54898

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2012-10-11 15:00:09 UTC ---
What happens is that the input at LTRANS stage has wrecked TYPE_MAIN_VARIANT:

(gdb) call debug_tree ($31)
 <integer_type 0x7ffff692a348 wchar_t readonly SI
    size <integer_cst 0x7ffff67f40a0 type <integer_type 0x7ffff67f00a8
bitsizetype> constant 32>
    unit size <integer_cst 0x7ffff67f40c0 type <integer_type 0x7ffff67f0000
sizetype> constant 4>
    align 32 symtab 0 alias set -1 structural equality precision 32 min
<integer_cst 0x7ffff6912880 -2147483648> max <integer_cst 0x7ffff6912a40
2147483647>>
(gdb) p $31->type_common.main_variant 
$32 = (tree) 0x7ffff6924540
(gdb) call debug_tree ($32)
 <integer_type 0x7ffff6924540 wchar_t SI
    size <integer_cst 0x7ffff67f40a0 type <integer_type 0x7ffff67f00a8
bitsizetype> constant 32>
    unit size <integer_cst 0x7ffff67f40c0 type <integer_type 0x7ffff67f0000
sizetype> constant 4>
    align 32 symtab 0 alias set -1 structural equality precision 32 min
<integer_cst 0x7ffff67f4040 -2147483648> max <integer_cst 0x7ffff67f4060
2147483647> context <translation_unit_decl 0x7ffff6927170 D.2440>>
(gdb) p $31->type_common.main_variant->type_common.main_variant 
$33 = (tree) 0x7ffff67f05e8
(gdb) call debug_tree ($33)
 <integer_type 0x7ffff67f05e8 int public SI
    size <integer_cst 0x7ffff67f40a0 type <integer_type 0x7ffff67f00a8
bitsizetype> constant 32>
    unit size <integer_cst 0x7ffff67f40c0 type <integer_type 0x7ffff67f0000
sizetype> constant 4>
    align 32 symtab 0 alias set -1 canonical type 0x7ffff67f05e8 precision 32
min <integer_cst 0x7ffff67f4040 -2147483648> max <integer_cst 0x7ffff67f4060
2147483647>
    pointer_to_this <pointer_type 0x7ffff67f82a0>>

thus a TYPE_MAIN_VARIANT of a main variant is not itself.  The code
cannot deal with this impossible situation.  Thus,
TYPE_MAIN_VARIANT (t) == TYPE_MAIN_VARIANT (TYPE_MAIN_VARIANT (t))
needs to always hold.

It might be that things break here because $33 is integer_type_node, a
type we pre-load into the streamer cache.

More investigation needed.