[Bug target/106069] [12/13 Regression] wrong code with -O -fno-tree-forwprop -maltivec on ppc64le

[luoxhu at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106069

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

Trying 188 -> 199:
  188: r343:V4SI=vec_select(vec_concat(r168:V4SI,r338:V4SI),parallel)
      REG_DEAD r338:V4SI
      REG_DEAD r168:V4SI
  199: {r353:SI=vec_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 = 12
replacement costs 4 + 8 = 12
modifying insn i2   188:
r343:V4SI=vec_select(vec_concat(r168:V4SI,r338:V4SI),parallel)
      REG_DEAD r168:V4SI
deferring rescan insn with uid = 188.
modifying insn i3   199: {r353:SI=vec_select(r338:V4SI,parallel);clobber
scratch;}
      REG_DEAD r338:V4SI
deferring rescan insn with uid = 199.