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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109048] [13 regression] redundant mask
 compare generated by vectorizer.
Date: Mon, 27 Mar 2023 10:37:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109048

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #8)
> Created attachment 54762 [details]
> heuristic
>=20
> I am testing this heuristic

FAIL: gcc.dg/tree-ssa/ranger-threader-3.c scan-tree-dump-times ethread
"Register
ing.*jump thread" 1
FAIL: gcc.dg/tree-ssa/ssa-dom-thread-14.c scan-tree-dump-times dom2 "Thread=
ed"
2

is the fallout - both are the same testcase, both can be mitigated by adjus=
ting
the dump to scan for and making sure PROP_loop_opts_done is also provided
for functions without loops.

But it also shows a case where we optimize things significantly later
after the change.

  if ((!unsignedp || (!left && methods =3D=3D OPTAB_WIDEN)))
    {
      enum optab_methods methods1 =3D methods;
      if (unsignedp)
        methods1 =3D OPTAB_MUST_WIDEN;
      expand_binop (left ? lshift_optab : rshift_arith_optab,
                           unsignedp, methods1);

used to be threaded in early threading but now would be delayed to after
loop opts.=