https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119402
--- Comment #3 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> Started with r14-5673-g33c2b70dbabc02788caabcbc66b7baeafeb95bcf
> With -O2 -mtune=generic it is fine even on the current trunk.
Seems like it's due to missing foldings.
the GIMPLE is the same, but when expended the cost model correctly tell the
backend that multiply isn't that expensive.
So we now expand to:
(insn 7 6 8 (set (reg:SI 109 [ _2 ])
(mult:SI (reg/v:SI 106 [ iftmpD.4457 ])
(reg/v:SI 107 [ _6D.4458 ]))) "/app/example.c":4:26 -1
(nil))
vs previous:
(insn 7 6 8 (set (reg:SI 109)
(neg:SI (reg/v:SI 106 [ iftmpD.4457 ]))) "/app/example.c":4:26 -1
(nil))
(insn 8 7 9 (set (reg:SI 110 [ _2 ])
(and:SI (reg:SI 109)
(reg/v:SI 107 [ _6D.4458 ]))) "/app/example.c":4:26 -1
(nil))
Which then causes:
Trying 8 -> 9:
8: r110:SI=~r107:SI
REG_DEAD r107:SI
9: r108:SI=r109:SI&r110:SI
REG_DEAD r110:SI
REG_DEAD r109:SI
Successfully matched this instruction:
(set (reg:SI 108 [ _4 ])
(and:SI (not:SI (reg/v:SI 107 [ _6D.4458 ]))
(reg:SI 109 [ _2 ])))
allowing combination of insns 8 and 9
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 8.
modifying insn i3 9: r108:SI=~r107:SI&r109:SI
REG_DEAD r107:SI
REG_DEAD r109:SI
deferring rescan insn with uid = 9.
Trying 7 -> 9:
7: r109:SI=r106:SI*r107:SI
REG_DEAD r106:SI
9: r108:SI=~r107:SI&r109:SI
REG_DEAD r107:SI
REG_DEAD r109:SI
Failed to match this instruction:
(set (reg:SI 108 [ _4 ])
(and:SI (mult:SI (reg/v:SI 106 [ iftmpD.4457 ])
(reg/v:SI 107 [ _6D.4458 ]))
(not:SI (reg/v:SI 107 [ _6D.4458 ]))))
vs previous:
Trying 9 -> 10:
9: r111:SI=~r107:SI
REG_DEAD r107:SI
10: r108:SI=r110:SI&r111:SI
REG_DEAD r111:SI
REG_DEAD r110:SI
Successfully matched this instruction:
(set (reg:SI 108 [ _4 ])
(and:SI (not:SI (reg/v:SI 107 [ _6D.4458 ]))
(reg:SI 110 [ _2 ])))
allowing combination of insns 9 and 10
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 9.
modifying insn i3 10: r108:SI=~r107:SI&r110:SI
REG_DEAD r107:SI
REG_DEAD r110:SI
deferring rescan insn with uid = 10.
Trying 8 -> 10:
8: r110:SI=r109:SI&r107:SI
REG_DEAD r109:SI
10: r108:SI=~r107:SI&r110:SI
REG_DEAD r107:SI
REG_DEAD r110:SI
Successfully matched this instruction:
(set (reg:SI 108 [ _4 ])
(const_int 0 [0]))
allowing combination of insns 8 and 10
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 8.
deferring deletion of insn with uid = 18.
deferring deletion of insn with uid = 3.
deferring deletion of insn with uid = 2.
deferring deletion of insn with uid = 7.
modifying insn i3 10: r108:SI=0
deferring rescan insn with uid = 10.
Seems like it's better to handle this at the GIMPLE level like we do today for
the z case.
