[PATCH 1/2] cselib: Keep track of further subvalue relations

[Stefan Schulze Frielinghaus via Gcc-patches]

Whenever a new cselib value is created check whether a smaller value
exists which is contained in the bigger one.  If so add a subreg
relation to locs of the smaller one.

gcc/ChangeLog:

        * cselib.cc (new_cselib_val): Keep track of further subvalue
        relations.
---
 gcc/cselib.cc | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/gcc/cselib.cc b/gcc/cselib.cc
index 6a5609786fa..9b582e5d3d6 100644
--- a/gcc/cselib.cc
+++ b/gcc/cselib.cc
@@ -1569,6 +1569,26 @@ 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_iter;
+      FOR_EACH_MODE_UNTIL (narrow_mode_iter, int_mode)
+       {
+         PUT_MODE_RAW (copy, narrow_mode_iter);
+         cselib_val *v = cselib_lookup (copy, narrow_mode_iter, 0, VOIDmode);
+         if (v)
+           {
+             rtx sub = lowpart_subreg (narrow_mode_iter, 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);
-- 
2.37.2