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From: "luoxhu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/106069] [12/13 Regression] wrong code with -O
 -fno-tree-forwprop -maltivec on ppc64le
Date: Thu, 30 Jun 2022 08:15:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106069

--- Comment #5 from luoxhu at gcc dot gnu.org ---
Seems combine wrongly merged two vec_select instructions:

Trying 188 -> 199:
  188: r343:V4SI=3Dvec_select(vec_concat(r168:V4SI,r338:V4SI),parallel)
      REG_DEAD r338:V4SI
      REG_DEAD r168:V4SI
  199: {r353:SI=3Dvec_select(r343:V4SI,parallel);clobber scratch;}
Failed to match this instruction:
(parallel [
        (set (reg:SI 353)
            (vec_select:SI (reg:V4SI 338)
                (parallel [
                        (const_int 3 [0x3])
                    ])))
        (clobber (scratch:V4SI))
        (set (reg:V4SI 343)
            (vec_select:V4SI (vec_concat:V8SI (reg/v:V4SI 168 [ R02$m_simd =
])
                    (reg:V4SI 338))
                (parallel [
                        (const_int 2 [0x2])
                        (const_int 6 [0x6])
                        (const_int 3 [0x3])
                        (const_int 7 [0x7])
                    ])))
    ])
Failed to match this instruction:
(parallel [
        (set (reg:SI 353)
            (vec_select:SI (reg:V4SI 338)
                (parallel [
                        (const_int 3 [0x3])
                    ])))
        (set (reg:V4SI 343)
            (vec_select:V4SI (vec_concat:V8SI (reg/v:V4SI 168 [ R02$m_simd =
])
                    (reg:V4SI 338))
                (parallel [
                        (const_int 2 [0x2])
                        (const_int 6 [0x6])
                        (const_int 3 [0x3])
                        (const_int 7 [0x7])
                    ])))
    ])
Successfully matched this instruction:
(set (reg:V4SI 343)
    (vec_select:V4SI (vec_concat:V8SI (reg/v:V4SI 168 [ R02$m_simd ])
            (reg:V4SI 338))
        (parallel [
                (const_int 2 [0x2])
                (const_int 6 [0x6])
                (const_int 3 [0x3])
                (const_int 7 [0x7])
            ])))
Successfully matched this instruction:
(set (reg:SI 353)
    (vec_select:SI (reg:V4SI 338)
        (parallel [
                (const_int 3 [0x3])
            ])))
allowing combination of insns 188 and 199
original costs 4 + 8 =3D 12
replacement costs 4 + 8 =3D 12
modifying insn i2   188:
r343:V4SI=3Dvec_select(vec_concat(r168:V4SI,r338:V4SI),parallel)
      REG_DEAD r168:V4SI
deferring rescan insn with uid =3D 188.
modifying insn i3   199: {r353:SI=3Dvec_select(r338:V4SI,parallel);clobber
scratch;}
      REG_DEAD r338:V4SI
deferring rescan insn with uid =3D 199.=