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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/99927] [11 Regression] Maybe wrong code since
 r11-39-gf9e1ea10e657af9f
Date: Tue, 06 Apr 2021 14:17:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99927

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Trying 105, 107 -> 108:
  105: r135:QI=3D0x1
  107: flags:CCZ=3Dcmp(r107:SI,0)
  108: r96:QI=3D{(flags:CCZ=3D=3D0)?r107:SI#0:r135:QI}
      REG_DEAD r107:SI
      REG_DEAD flags:CC
Failed to match this instruction:
(parallel [
        (set (reg:QI 96 [ var_lsm_flag.12 ])
            (subreg:QI (reg:SI 107) 0))
        (set (reg:QI 135)
            (const_int 1 [0x1]))
    ])
Failed to match this instruction:
(parallel [
        (set (reg:QI 96 [ var_lsm_flag.12 ])
            (subreg:QI (reg:SI 107) 0))
        (set (reg:QI 135)
            (const_int 1 [0x1]))
    ])
Successfully matched this instruction:
(set (reg:QI 135)
    (const_int 1 [0x1]))
Successfully matched this instruction:
(set (reg:QI 96 [ var_lsm_flag.12 ])
    (subreg:QI (reg:SI 107) 0))
allowing combination of insns 105, 107 and 108
original costs 4 + 4 + 8 =3D 16
replacement costs 4 + 4 =3D 8
deferring deletion of insn with uid =3D 105.
modifying insn i2   107: r135:QI=3D0x1
deferring rescan insn with uid =3D 107.
modifying insn i3   108: r96:QI=3Dr107:SI#0
      REG_DEAD r107:SI
deferring rescan insn with uid =3D 108.

note that insn 107 was the CC setter for the if-then-else but we now have
a plain move there.=