"Unknown" Instruction in Specific Instruction Sequence Did Not Trigger Exception Correctly

[fly-1011]

Describe the bug

When using nemu as a reference model to test Xiangshan, I found that for unknown instructions in a specific instruction sequence, nemu could not correctly cause an illegal instruction exception.

The following is a screenshot of the log information：

This is the test program and log information：test.zip

Necessary information on versions

• NEMU version: 2df9c44
• xiangshan:commit 77733a7b1f4626cf325c130e7d7b560ff57aec80
• ready-to-run: commit 98f779c914017c6fcf173a81c492a77aa9692dbb

[NewPaulWalker]

Thank you for your issue. I found that this is due to a problem with the decoding of the vslide instruction in NEMU. Some vslide instructions had redundant and incorrect decoding, which I have now fixed by #770.