[Bug debug/100960] var-tracking: parameter location in subregister not tracked

["stefansf at linux dot ibm.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100960

--- Comment #4 from Stefan Schulze Frielinghaus <stefansf at linux dot ibm.com> ---
I really like the idea of enhancing cselib since there is a chance that other
passes might profit from it, too. The following patch fixes the initial
reported problem:

diff --git a/gcc/cselib.cc b/gcc/cselib.cc
index 6a5609786fa..64b6996a299 100644
--- a/gcc/cselib.cc
+++ b/gcc/cselib.cc
@@ -1569,6 +1569,25 @@ new_cselib_val (unsigned int hash, machine_mode mode,
rtx x)
   e->locs = 0;
   e->next_containing_mem = 0;

+  scalar_int_mode int_mode;
+  if (REG_P (x) && is_int_mode (mode, &int_mode) && REG_VALUES (REGNO (x)) !=
NULL
+      && (!cselib_current_insn || !DEBUG_INSN_P (cselib_current_insn)))
+    {
+      rtx copy = shallow_copy_rtx (x);
+      scalar_int_mode narrow_mode;
+      FOR_EACH_MODE_UNTIL(narrow_mode, int_mode)
+       {
+         PUT_MODE_RAW (copy, narrow_mode);
+         cselib_val *v = cselib_lookup (copy, narrow_mode, 0, VOIDmode);
+         if (v)
+           {
+             rtx sub = lowpart_subreg (narrow_mode, e->val_rtx, int_mode);
+             if (sub)
+               new_elt_loc_list (v, sub);
+           }
+       }
+    }
+
   if (dump_file && (dump_flags & TDF_CSELIB))
     {
       fprintf (dump_file, "cselib value %u:%u ", e->uid, hash);

So I get the subvalue relation between 5:5 and 14:14 (was initially 15:15 but
changed meanwhile due to new GCC version)

(value/u:SI 5:5 @0x4f906e0/0x4f80730)
 locs:
  from insn 17 (subreg:SI (value/u:DI 14:14 @0x4f907b8/0x4f808e0) 4)
  from insn 1 (value/u:SI 6:263 @0x4f906f8/0x4f80760)
  from insn 1 (entry_value:SI (reg:SI 2 %r2 [ xD.2274 ]))
 no addrs