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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/106220] x86-64 optimizer forgets about shrd peephole
 optimization pattern when faced with more than one in close proximity
Date: Fri, 11 Nov 2022 05:05:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106220

--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
Try to add combine splitter

(define_insn_and_split "*x86_64_shrd_lshiftrtti"
  [(set (match_operand:DI 0 "nonimmediate_operand")
        (subreg:DI (lshiftrt:TI (match_operand:TI 1 "nonimmediate_operand")
                                (subreg:QI
                                  (and:SI
                                    (match_operand:SI 2 "register_operand")
                                    (const_int 63)) 0)) 0))
   (clobber (reg:CC FLAGS_REG))]

 but failed if there's more than 2 shrd insns since there's flags clobber in
the first shrd which prevent the second shrd to be combined. By the time it=
's
splitted after reload, it's too later to optimize off redudant cmovne.=