[Bug debug/43516] [4.5 Regression] "-fcompare-debug failure" at -O2

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #11 from jakub at gcc dot gnu dot org  2010-03-26 11:03 -------
Ah, apparently the type returned by c_common_signed_type -> ... ->
build_nonstandard_integer_type is not referenced from anywhere anymore during
FRE, except from
static GTY ((if_marked ("type_hash_marked_p"), param_is (struct type_hash)))
     htab_t type_hash_table;
With -g0 at the end of FRE ggc_collect actually performs GC, while with -g it
doesn't at this point (different amount of memory allocated, ...).
As that signed 1 bit type isn't marked, it is removed from the hash table and
therefore during PRE when get_alias_set is called again on the unsigned 1 bit
type, this signed 1 bit type isn't found anymore and thus
build_nonstandard_integer_type returns a fresh new type.
BTW, even if GC didn't happen, type_hash_marked_p returns
return ggc_marked_p (type) || TYPE_SYMTAB_POINTER (type);
where TYPE_SYMTAB_POINTER depends on -g vs. -g0.
I think there can't be too many non-standard integer types, so perhaps just
build_nonstandard_type should make sure whatever it once returns isn't garbage
collected.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43516