https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109279
--- Comment #17 from Vineet Gupta <vineetg at gcc dot gnu.org> ---
(In reply to Vineet Gupta from comment #16)
> > Which is what this produces:
> > ```
> > long long f(void)
> > {
> > unsigned t = 16843009;
> > long long t1 = t;
> > long long t2 = ((unsigned long long )t) << 32;
> > asm("":"+r"(t1));
> > return t1 | t2;
> > }
> > ```
>
> li a0,16842752
> addi a0,a0,257
> li a5,16842752
> slli a0,a0,32
> addi a5,a5,257
> or a0,a5,a0
> ret
This is again IRA inflicted pain (similar to [PR110748]).
IRA seems to be undoing split1 since we have 2 insn sequences to synthesize the
constant pieces. This explains why the problem got exacerbated with commit
0530254413f8 ("riscv: relax splitter restrictions for creating pseudos") since
now different regs are used to create parts of const, vs 1 reg being repeatedly
used for assembling a const (fooling IRA's equivalent replacement logic).
