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From: "hubicka at ucw dot cz" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ipa/102581] [12 Regression] ice in forced_merge, at
 ipa-modref-tree.h:352 with -fno-strict-aliasing and -O2 since
 r12-3202-gf5ff3a8ed4ca9173
Date: Wed, 06 Oct 2021 15:16:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102581

--- Comment #8 from Jan Hubicka <hubicka at ucw dot cz> ---
Actually, this is shorter patch - we already should notice that one
range is contained in other, but we give up too early.

Honza

diff --git a/gcc/ipa-modref-tree.h b/gcc/ipa-modref-tree.h
index 6a9ed5ce54b..8e9b89b3e2c 100644
--- a/gcc/ipa-modref-tree.h
+++ b/gcc/ipa-modref-tree.h
@@ -110,8 +110,11 @@ struct GTY(()) modref_access_node
               if (!a.parm_offset_known)
                 return false;
               /* Accesses are never below parm_offset, so look
-                 for smaller offset.  */
-              if (!known_le (parm_offset, a.parm_offset))
+                 for smaller offset.
+                 If access ranges are known still allow merging
+                 when bit offsets comparsion passes.  */
+              if (!known_le (parm_offset, a.parm_offset)
+                  && !range_info_useful_p ())
                 return false;
               aoffset_adj =3D (a.parm_offset - parm_offset)
                             << LOG2_BITS_PER_UNIT;
@@ -618,6 +621,7 @@ private:
            found =3D true;
          if (!found && n->merge (*a, false))
            found =3D restart =3D true;
+         gcc_checking_assert (found || !a->merge (*n, false));
          if (found)
            {
              accesses->unordered_remove (i);=