https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51663
--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Tom de Vries from comment #13) > (In reply to Richard Biener from comment #12) > > (In reply to Tom de Vries from comment #11) > > > Cross-referencing PR gdb/25684 - "gdb testing with gcc -flto" ( > > > https://sourceware.org/bugzilla/show_bug.cgi?id=25684 ). > > > > > > Ideally there would be a way to enable the lto infrastructure without > > > actually optimizing, such that when running the gdb testsuite with and > > > without flto and comparing results, any regression would indicate > > > something > > > that needs fixing. > > > > > > In the current situation, each individual regression needs investigation > > > whether something needs fixing or whether the failure is just an > > > optimization artifact. And due to the fact there are optimizations, there > > > are thousands of such regressions. > > > > I suppose we're talking about -O0 -flto here. > > Right, and ideally -flto plain, with -O0 implicit. > > > What kind of transforms > > are undesirable? I think at -O0 you'll get > > > > - more aggressive unused variable/function removal > > - promotion of variables from global to local > > > > Right, is there a way to switch these off? Not at the moment I think. The main unused variable/function removal is in cgraphunit.c:analyze_functions. I guess the simplest thing would be to try diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c index a9dd288be57..3aa8137efad 100644 --- a/gcc/cgraphunit.c +++ b/gcc/cgraphunit.c @@ -1158,7 +1158,7 @@ analyze_functions (bool first_time) { /* Convert COMDAT group designators to IDENTIFIER_NODEs. */ node->get_comdat_group_id (); - if (node->needed_p ()) + if (!optimize || node->needed_p ()) { enqueue_node (node); if (!changed && symtab->dump_file) but I'm not sure this is enough since we remove not refered to things at several points during the compilation (including during partitioning I think). Another possibility would be to make all nodes force_output when not optimizing like with diff --git a/gcc/cgraph.h b/gcc/cgraph.h index aa4cdc95506..b07bf9745d0 100644 --- a/gcc/cgraph.h +++ b/gcc/cgraph.h @@ -115,7 +115,7 @@ public: transparent_alias (false), weakref (false), cpp_implicit_alias (false), symver (false), analyzed (false), writeonly (false), refuse_visibility_changes (false), externally_visible (false), - no_reorder (false), force_output (false), forced_by_abi (false), + no_reorder (false), force_output (optimize), forced_by_abi (false), unique_name (false), implicit_section (false), body_removed (false), used_from_other_partition (false), in_other_partition (false), address_taken (false), in_init_priority_hash (false), or in a more suitable place. That should eventually also avoid promotion to local. > > some of the transforms are unavoidable due to partitioning(?) but we could > > default to 1:1 partitioning at -O0 ... > > At this point I'm not interested in defaults yet. I can achieve 1:1 > partition by testing target board unix/-flto/-flto-partition=1to1. > > For now I'm interested in a combination of flags that exercises the specific > type of debug info generation as is done for lto, without actually doing any > optimizations. > > F.i., an open question for me is the following: I'm now using > -flto-partition=none for testing, but maybe 1to1 should yield better results?
