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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/108573] [13 Regression] '-fcompare-debug' failure
 (length) at -O2
Date: Tue, 31 Jan 2023 17:46:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108573

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/ree.cc.jj       2023-01-02 09:32:45.327953792 +0100
+++ gcc/ree.cc  2023-01-31 18:36:31.253018233 +0100
@@ -875,7 +875,8 @@ combine_reaching_defs (ext_cand *cand, c

          for (df_link *use =3D uses; use; use =3D use->next)
            if (paradoxical_subreg_p (GET_MODE (*DF_REF_LOC (use->ref)),
-                                     GET_MODE (SET_DEST (*dest_sub_rtx))))
+                                     GET_MODE (SET_DEST (*dest_sub_rtx)))=
=20
+               && !DEBUG_INSN_P (DF_REF_INSN (use->ref)))
              return false;
        }

fixes this particular -fcompare-debug failure.  Dunno though about get_uses=
, it
performs some checks and returns NULL if those fail (again, ignoring if the
failures are from DEBUG_INSNs or something else), plus in theory there coul=
d be
a non-NULL ref_chain of only debug uses (though hopefully we prevent that).
And there is another spot that would need the same change as above.=