On Thu, 20 Aug 2026, Jakub Jelinek wrote: > Hi! > > The r12-4397 change to get rid of AUTODETECT_VALUE unfortunately broke > several things related to -fvar-tracking-uninit. > Before that change, the option defaulted to 0, under some condition > on darwin only set it to flag_var_tracking which at that point could have > been whatever user specified or AUTODETECT_VALUE and finally in > finish_options did: > /* If the user specifically requested variable tracking with tagging > uninitialized variables, we need to turn on variable tracking. > (We already determined above that variable tracking is feasible.) */ > if (flag_var_tracking_uninit == 1) > flag_var_tracking = 1; > > if (flag_var_tracking == AUTODETECT_VALUE) > flag_var_tracking = optimize >= 1; > > if (flag_var_tracking_uninit == AUTODETECT_VALUE) > flag_var_tracking_uninit = flag_var_tracking; > i.e. > 1) -fvar-tracking-uninit option specified on command line implied > -fvar-tracking > 2) var-tracking was defaulted to 1 even for -O1 and above > 3) in the darwin conditional case if flag_var_tracking_uninit was > defaulted to maybe on, it was set to flag_var_tracking > > The r12-4397 change properly handled only 2), by adding > default_options_table entry for OPT_fvar_tracking. > 1) got lost in the patch, -fvar-tracking-uninit explicitly on command > line no longer implies -fvar-tracking > 3) was probably assumed to be always initialized to AUTODETECT_VALUE > and so replaced with > /* One could use EnabledBy, but it would lead to a circular dependency. */ > if (!OPTION_SET_P (flag_var_tracking_uninit)) > flag_var_tracking_uninit = flag_var_tracking; > which effectively makes -fvar-tracking-uninit default to on whenever > -fvar-tracking is on (explicitly or implicitly), unless overridden by user. > > Also note that the value of flag_var_tracking_uninit is irrelevant if > flag_var_tracking is off, the variable is only tested in various spots > in the var-tracking pass guarded by flag_var_tracking. > > Anyway, the following patch restores the 1) behavior, changes the > darwin code to just set flag_var_tracking_uninit by default to 1 if > the condition is met (worst case flag_var_tracking_uninit will be 1 > and flag_var_tracking will be 0, nothing will care), drops the bogus > defaulting to -fvar-tracking-uninit on all other targets and finally fixes > something that has been broken even before r12-4397, in my reading on > darwin the condition would turn on flag_var_tracking_uninit even if > user used explicit -fno-var-tracking-uninit. > > Unfortunately the DW_OP_GNU_uninit support didn't come with a single > testcase, neither on the gcc side nor on the gdb side and I haven't figured > out easily a testcase which I could add to the testsuite for this (sure, I > could from some *.o that contains it cvise reduce it). > But one can actually see some DW_OP_GNU_uninit uses in the cc1plus binary, > before the patch: > readelf -wo cc1plus 2>&1 | grep DW_OP_GNU_uninit | wc -l > 2228 > readelf -wo cc1plus 2>&1 | grep DW_OP_GNU_uninit.*DW_OP_GNU_uninit | wc -l > 208 > after the patch: > readelf -wo cc1plus 2>&1 | grep DW_OP_GNU_uninit | wc -l > 0 > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK. Thanks, Richard. > 2026-08-20 Jakub Jelinek <[email protected]> > > PR debug/126801 > * opts.cc (finish_options): Don't set flag_var_tracking_uninit to > flag_var_tracking by default. Instead, set flag_var_tracking to > flag_var_tracking_uninit if the latter was explicitly set. > * config/darwin.cc (darwin_override_options): Only set > flag_var_tracking_uninit if it wasn't explicitly set and set it to > 1 rather than flag_var_tracking. Formatting fix. > > --- gcc/opts.cc.jj 2026-08-18 08:47:22.044793076 +0200 > +++ gcc/opts.cc 2026-08-19 12:28:11.107209028 +0200 > @@ -1499,9 +1499,8 @@ finish_options (struct gcc_options *opts > opts->x_flag_var_tracking_assignments = 0; > } > > - /* One could use EnabledBy, but it would lead to a circular dependency. */ > - if (!opts_set->x_flag_var_tracking_uninit) > - opts->x_flag_var_tracking_uninit = opts->x_flag_var_tracking; > + if (opts_set->x_flag_var_tracking_uninit && > opts->x_flag_var_tracking_uninit) > + opts->x_flag_var_tracking = 1; > > if (!opts_set->x_flag_var_tracking_assignments) > opts->x_flag_var_tracking_assignments > --- gcc/config/darwin.cc.jj 2026-08-17 10:00:21.681856778 +0200 > +++ gcc/config/darwin.cc 2026-08-19 12:24:08.235382015 +0200 > @@ -3576,12 +3576,13 @@ darwin_override_options (void) > flag_asynchronous_unwind_tables = 0; > } > > - if (flag_var_tracking_uninit == 0 > + if (!OPTION_SET_P (flag_var_tracking_uninit) > + && flag_var_tracking_uninit == 0 > && generating_for_darwin_version >= 9 > && (flag_gtoggle ? (debug_info_level == DINFO_LEVEL_NONE) > - : (debug_info_level >= DINFO_LEVEL_NORMAL)) > + : (debug_info_level >= DINFO_LEVEL_NORMAL)) > && dwarf_debuginfo_p ()) > - flag_var_tracking_uninit = flag_var_tracking; > + flag_var_tracking_uninit = 1; > > if (OPTION_SET_P (flag_pie) && flag_pie) > { > > Jakub > > -- Richard Biener <[email protected]> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Jochen Jaser, Andrew McDonald, Abhinav Puri; (HRB 36809, AG Nuernberg)
