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From: "linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug debug/105627] -fcompare-debug failure at -Og for
 powerpc64le-unknown-linux-gnu
Date: Thu, 19 May 2022 07:28:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105627

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |linkw at gcc dot gn=
u.org

--- Comment #2 from Kewen Lin <linkw at gcc dot gnu.org> ---
Thanks for reporting and triaging.

Although loops in function rs6000_analyze_swaps only handles NONDEBUG_INSN_P
insns, when doing unionfind_union it's still possible to union with debug i=
nsn,
as some def reg of nondebug insn can be used in debug insn, it makes the un=
ions
become different unexpectedly.=20

The below patch can fix the issue, I don't think we need the similar handli=
ng
in union_defs as I feel it's impossible to have the case that one reg which=
 is
defined by debug insn but used in nondebug insn.

diff --git a/gcc/config/rs6000/rs6000-p8swap.cc
b/gcc/config/rs6000/rs6000-p8swap.cc
index d301bc3fe59..3aa90034c29 100644
--- a/gcc/config/rs6000/rs6000-p8swap.cc
+++ b/gcc/config/rs6000/rs6000-p8swap.cc
@@ -242,8 +242,9 @@ union_uses (swap_web_entry *insn_entry, rtx insn, df_ref
def)
       if (DF_REF_INSN_INFO (link->ref))
         {
           rtx use_insn =3D DF_REF_INSN (link->ref);
-          (void)unionfind_union (insn_entry + INSN_UID (insn),
-                                 insn_entry + INSN_UID (use_insn));
+          if (NONDEBUG_INSN_P (use_insn))
+            (void) unionfind_union (insn_entry + INSN_UID (insn),
+                                    insn_entry + INSN_UID (use_insn));
         }=