https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70594
--- Comment #9 from Patrick Palka <ppalka at gcc dot gnu.org> --- (In reply to Nathan Sidwell from comment #7) > The change in debug generation causes purtabations in when GC happens. > Such that in onecase we find a cached result, and in the other case we do > not. When we don't we end up here: > > 0 allocate_decl_uid () at ../../../src/gcc/tree.c:990 > #1 0x0000000001362a01 in copy_node_stat (node=0x7ffff6093e10) at > ../../../src/gcc/tree.c:1157 > #2 0x00000000010f1a97 in copy_decl_no_change (decl=0x7ffff6093e10, > id=0x7fffffffb120) at ../../../src/gcc/tree-inline.c:5444 > #3 0x00000000010e0ebe in remap_decl (decl=0x7ffff6093e10, > id=0x7fffffffb120) at ../../../src/gcc/tree-inline.c:357 > #4 0x00000000010f45fe in copy_fn (fn=0x7ffff6168c40, parms=@0x7ffff6683a28: > 0x0, result=@0x7ffff6683a30: 0xafafafafafafafaf) > at ../../../src/gcc/tree-inline.c:6148 > #5 0x00000000009ec170 in get_fundef_copy (fun=0x7ffff6168c40) at > ../../../src/gcc/cp/constexpr.c:1021 > > copy_node_stat allocates a new UID for decls. so despite its name > 'copy_decl_no_change' does cause a change. > > That decl never escapes out of the const-expr machinery, but of cause causes > later decls to have different numberings. (which is what we're observing). > > I suppose the constexpr machinery could restore the next_decl_uid (and > perhaps others?) after copy_fn -- or somewhere in that call chain. But that > does seem rather icky. > > Alternatively copy_decl_no_change could not allocate new UIDs? The decls belonging to a copy of a function must have new UIDs though because their uids are used to track their mutable values (within the constexpr_ctx::values hash_map). So if the decls of two copies of the same function didn't have different uids then e.g. recursive function calls wouldn't get evaluated properly. > > Anyway, hope that helps. > > For reference, the difference happens with a call to finish_return_stmt at > parser.c:11808 when input_location == 17095968. We eventually end up in > cxx_eval_call_expression where the call: > constexpr_call **slot > = constexpr_call_table->find_slot (&new_call, INSERT); > (line 1433) finds a non-empty slot in one case and not in the other. > (constexpr_call_table is a deletable hash)
