[Bug target/112438] RISC-V: Failed to AVL propagation through induction variable

[kito at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112438

--- Comment #6 from Kito Cheng <kito at gcc dot gnu.org> ---
The key is the splat of VLMAX instruction need move into loop body, but AVL
propagation should still able to do:

```
foo(int, int*, int*):
        ble     a0,zero,.L5
        csrr    a5,vlenb
        srli    a5,a5,2
        vsetvli a3,zero,e32,m1,ta,ma
        vid.v   v2
.L3:
        vsetvli a5,a0,e32,m1,ta,ma
        slli    a4,a5,2
        vle32.v v1,0(a1)
        sub     a0,a0,a5
        vadd.vv v1,v1,v2
        vse32.v v1,0(a2)
        add     a1,a1,a4
        vmv.v.x v4,a5           # Move to here, splat vl to a5 rather than
VLMAX
        vsetvli a5,zero,e32,m1,ta,ma --- > redundant

        add     a2,a2,a4
        vadd.vv v2,v2,v4
        bne     a0,zero,.L3
.L5:
        ret
```