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?
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
