On Fri, Jan 25, 2019 at 7:57 AM Richard Biener <rguent...@suse.de> wrote: > > The following fixes an ICE with -flto -ffat-lto-objects > -fdebug-types-section -g where optimize_external_refs does not > expect to see DW_AT_signature as made "local" by build_abbrev_table(sic!). > > This is because we run optimize_external_refs twice in this setup. > > The fix is to make the second run not pick up "local" DW_AT_signature > as external. Alternatively build_abbrev_table could be adjusted > to not keep those as DW_AT_signature. It's not even clear to me > whether a DW_AT_signature as we output it is valid DWARF ... > to quote non-LTO -g: > > <1><1d>: Abbrev Number: 13 (DW_TAG_structure_type) > <1e> DW_AT_name : (indirect string, offset: 0x8b): > integral_constant<bool, false> > <22> DW_AT_signature : <0x5d>
Yes, that seems pretty clearly wrong. It doesn't make sense for DW_AT_signature to be a local reference; it should only have DW_FORM_ref_sig8. > <26> DW_AT_declaration : 1 > <26> DW_AT_sibling : <0x48> > ... > <1><5d>: Abbrev Number: 16 (DW_TAG_structure_type) > <5e> DW_AT_name : (indirect string, offset: 0x8b): > integral_constant<bool, false> > <62> DW_AT_signature : signature: 0x1f6a4ae7cc5a362e > <6a> DW_AT_declaration : 1 > <6a> DW_AT_sibling : <0x7b> And there's no reason to have two skeleton DIEs for the same type. > Of course the main "issue" is that copy_unworthy_types > duplicated this parent into 1d and 5d in the first place > (but that's a pure optimization issue?). Indeed. > Not doing that > would have avoided the situation in PR87295. But then > why should optimize_external_refs_1 have this special > code handling DW_AT_signature in the first place if this > was not intended... (so even better, kill that and the > build_abbrev_table optimization and fix copy_unworthy_types?) The point of optimize_external_refs_1 is to remember when we've seen a skeleton DIE so we can refer to it from other DIEs in the same unit rather than use DW_FORM_ref_sig8. The problem is just that we get two skeleton DIEs so we wrongly change one to refer to the other. One possibility would be to suppress the local reference optimization for DW_AT_signature, but avoiding the redundant skeleton should fix the problem and also save space. > Oh, and insert rants of -fdebug-types-section not being > used by anybody. Jakub, what's your thinking on -fdebug-types-section these days? Jason
