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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/104581] [12 Regression] Huge compile-time regression
 building SPEC 2017 538.imagick_r with PGO
Date: Thu, 17 Feb 2022 12:35:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104581

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Since targetm.mode_switching.needed is called as part of the mode-switching
dataflow problem I don't see how looking at reg refs should be needed at al=
l.
What might be needed and what I'm not sure is available, is the mode-switch=
ing
state of uses.  The relevant call is

          FOR_BB_INSNS (bb, insn)
            {
              if (INSN_P (insn))
                {
                  int mode =3D targetm.mode_switching.needed (e, insn);

and indeed all the time is spent in

        /* Check if DEF_INSN is before INSN.  */
        rtx_insn *next;
        for (next =3D NEXT_INSN (def_insn);
             next !=3D nullptr && next !=3D end && next !=3D insn;
             next =3D NEXT_INSN (next))
          ;=