ara_dispatcher handling of continuous Configuration-Setting Instructions (vsetvli/vsetivli/vsetvl) is not perfect.

[WEIhabi]

Enter two Config instructions in ara_dispatcher, as follows

1. vsetvl x0, x16, e8, m8, tu, mu (32'h8038_7057) # SEW= 8, LMUL=8
2. vsetvli x0, x0, e16, m1, tu, ma (32'h3880_7057) # SEW= 16, LMUL=1

This sets LMUL=1 and vl=1040 (from rs1 in the vsetvl instruction) for subsequent instructions, causing subsequent instructions to be written to destination registers where they should not be.

The reason is that ara_dispatcher violates the rule that the original vl value cannot be preserved when VLMAX and vl change due to a new SEW/LMUL ratio, which is currently preserved, and the implementation should go to set vill or VL set to VLMAX due to the AVL > VLMAX (RVV SPEC 6.3 3. vl = VLMAX if AVL ≥ (2 * VLMAX) ).

If the development team wants to be compatible with spike, there is also a treatment for this in the implementation of spike, which selects the value of min.

The following diagram shows the relevant waveforms:
You can see the final change of the vslideup instruction from the original vd=v9 to v17.

[mp-17]

Hello @WEIhabi, thanks a lot for reporting!! :-)
I will fix this asap in the next round of bug fixes.

Best,
Matteo