[gcc r17-3469] Fix up -fvar-tracking-uninit [PR126801]

https://gcc.gnu.org/g:7e784194fe49e45c8fb78168064a9b2627493f09

commit r17-3469-g7e784194fe49e45c8fb78168064a9b2627493f09
Author: Jakub Jelinek <[email protected]>
Date:   Thu Aug 20 12:35:41 2026 +0200

    Fix up -fvar-tracking-uninit [PR126801]
    
    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
    
    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.
    
    Reviewed-by: Richard Biener <[email protected]>

Diff:
---
 gcc/config/darwin.cc | 7 ++++---
 gcc/opts.cc          | 5 ++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/gcc/config/darwin.cc b/gcc/config/darwin.cc
index 2f8232989631..ba934c264022 100644
--- a/gcc/config/darwin.cc
+++ b/gcc/config/darwin.cc
@@ -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)
     {
diff --git a/gcc/opts.cc b/gcc/opts.cc
index 7eabab9b2e12..8048264b6099 100644
--- a/gcc/opts.cc
+++ b/gcc/opts.cc
@@ -1499,9 +1499,8 @@ finish_options (struct gcc_options *opts, struct gcc_options *opts_set,
       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