[Bug debug/99830] [11 Regression] ICE: in lra_eliminate_regs_1, at lra-eliminations.c:659 with -O2 -fno-expensive-optimizations -fno-split-wide-types -g

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99830

--- Comment #12 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #11)
> I don't understand what is wrong about that.
> (clobber:TI (const_int 0 [0])) in there stands for couldn't figure out what
> this value is or how to represent it, so it is wildcard for I don't know
> what the value is.

That is not what it means.  It means "This instruction is invalid".  It should
never be "optimised" away.

> I'd think if one has say (and:TI (clobber:TI (const_int 0 [0])) (const_int 0
> [0])) one should be able to still simplify it into 0, etc.,

No.  That RTL has no meaning at all, you cannot use a clobber as a RHS!

> and what happens
> here is the same thing, the clobber value, whatever it is, doesn't influence
> in any way the whole expression value, therefore it is optimized away.
> If it remained there, sure, the instruction would fail recog_for_combine.

Yes.  And that is why it should never be removed!