When rd is x0, the c.ldsp instruction does not cause an illegal instruction exception

[fly-1011]

Bug Description:

When executing the c.ldsp zero, 304 (sp) instruction, the behavior of the NutShell processor and spike is different.
According to the riscv specification, when the target register is zero, an illegal instruction exception should be caused, but NutShell does not.

Assembly Code

.section .text
.globl _start
_start:
    li sp,0x0
    .word 0x7052 #c.ldsp zero, 304 (sp)

Screenshots

Expected behavior

NutShell should cause the same illegal instruction exception as spile

Version Information

NutShell:commit 61923a1 (HEAD, origin/master, origin/HEAD)