[Bug rtl-optimization/82683] Combine: GCC generates bad code with -tune=thunderx2t99

[wilco at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82683

--- Comment #6 from Wilco <wilco at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #5)
> Oh, it does show the intermediate results:
> 
> Trying 18 -> 19:
> Successfully matched this instruction:
> (set (reg/f:DI 78 [ _7 ])
>     (plus:DI (ashift:DI (reg:DI 83 [ _26 ])
>             (const_int 2 [0x2]))
>         (reg/f:DI 76 [ _4 ])))
> allowing combination of insns 18 and 19
> original costs 4 + 4 = 8
> replacement cost 8
> deferring deletion of insn with uid = 18.
> modifying insn i3    19: r78:DI=r83:DI<<0x2+r76:DI
>       REG_DEAD r83:DI
>       REG_DEAD r76:DI
> deferring rescan insn with uid = 19.
> 
> (How do you dump things?  You forgot a -all?)

Yes, but this is all it shows for the bit that goes wrong:

allowing combination of insns 19, 20 and 21
original costs 8 + 20 + 4 = 32
replacement costs 28 + 4 = 32
deferring rescan insn with uid = 21.
deferring deletion of insn with uid = 19.
modifying insn i2    20: r83:DI=sign_extend([r83:DI*0x4+r76:DI])
      REG_DEAD r76:DI
deferring rescan insn with uid = 20.
modifying insn i3    21: r82:SI=r83:DI#0
      REG_DEAD r83:DI
      REG_DEAD r83:DI
      REG_DEAD r83:DI
deferring rescan insn with uid = 21.

I guess it would be good if it shows the instructions it's trying to combine in
this part, because it's impossible to follow when the instructions involved
have been changed already...