Insn combine trying (ior:HI (clobber:HI (const_int 0)))

[Richard Sandiford]

Georg-Johann Lay <avr@gjlay.de> writes:
> In a test case I see insn combine trying to match such
> expressions, which do not make any sense to me, like:
>
> Trying 2 -> 7:
>      2: r45:HI=r48:HI
>        REG_DEAD r48:HI
>      7: {r47:HI=r45:HI|r46:PSI#0;clobber scratch;}
>        REG_DEAD r46:PSI
>        REG_DEAD r45:HI
> Failed to match this instruction:
> (parallel [
>          (set (reg:HI 47 [ _4 ])
>              (ior:HI (clobber:HI (const_int 0 [0]))
>                  (reg:HI 48)))
>          (clobber (scratch:QI))
>      ])
>
> and many other occasions like that.
>
> Is this just insn combine doing its business?
>
> Or should this be some sensible RTL instead?
>
> Seen on target avr with v14 and trunk,
> attached test case and dump compiled with

(clobber:M (const_int 0)) is combine's way of representing
"something went wrong here".  And yeah, recog acts as an error
detection mechanism in these cases.  In other words, the idea
is that recog should eventually fail on nonsense rtl like that,
so earlier code doesn't need to check explicitly.

Richard

>
> $ avr-gcc-14 strange.c -S -Os -dp -da
>
> Johann