On Wed, 1 Mar 2023, Jason Merrill wrote: > On 3/1/23 08:09, Jakub Jelinek wrote: > > On Wed, Mar 01, 2023 at 01:07:02PM +0000, Richard Biener wrote: > >> When combining -g1 with -flto we run into the DIE location annotation > >> machinery for globals calling dwarf2out_late_global_decl but not > >> having any early generated DIE for function scope statics. In > >> this process we'd generate a limbo DIE since also the function scope > >> doesn't have any early generated DIE. The limbo handling then tries > >> to force a DIE for the context chain which ultimatively fails and > >> ICEs at the std namespace decl because at -g1 we don't represent that. > >> > >> The following avoids this situation by making sure to never generate > >> any limbo DIEs from dwarf2out_late_global_decl in the in_lto_p path > >> but instead for function scope globals rely on DIE generation for > >> the function to output a DIE for the local static (which doesn't > >> happen for -g1). > > So the issue is that we're trying to force out a DIE for a decl that we > wouldn't have generated without -flto? How is it avoided in the non-LTO case?
When we go rest_of_decl_compilation for this decl we defer to the containing function to generate an early DIE but that doesn't (because of -g1). The call to late_global_decl that's done by assemble_decl then does nothing because there's no early DIE. But with -flto we cannot completely rely on early DIE presence (not even without, in case of cloning - but we don't clone global variables), esp. because there's still the "supported" non-early-LTO path for non-ELF targets. So at this point it seems to be the best thing to mimic what rest_of_decl_compilation does and defer to dwarf2out of the containing function to generate the DIE (or not). For the reason of the least amount of changes at this point in stage4 I went for querying the DECL_CONTEXT DIE instead of right-out not handling local_function_static () decls in this path. If you'd prefer that, so if (! die && in_lto_p /* Function scope variables are emitted when emitting the DIE for the function. */ && ! local_function_static (decl)) dwarf2out_decl (decl); then I can test that variant as well which feels a bit more consistent. Thanks, Richard. > >> I explored a lot of other options to fix this but in the end this > >> seems to be the most spot-on fix with the least risk of unwanted > >> effects. > >> > >> LTO bootstrapped on x86_64-unknown-linux-gnu (running into PR108984), > >> bootstrapped and tested on x86_64-unknown-linux-gnu. > >> > >> OK? > >> > >> Thanks, > >> Richard. > >> > >> PR debug/108772 > >> * dwarf2out.cc (dwarf2out_late_global_decl): Do not > >> generate a DIE for a function scope static when we do > >> not have a DIE for the function already. > >> > >> * g++.dg/lto/pr108772_0.C: New testcase. > > > > LGTM, but please give Jason a day to chime in if he disagrees. > > > > Jakub > > > > > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)