Illegal shift instructions don't raise illegal instruction exceptions

[mmxsrup]

Observed Behavior

An illegal instruction exception should be raised when the shift amount of the shift instructions is 32 or more, as described in Chapter 4.2 of RISC-V User-Level ISA.

For RV32I, SLLI, SRLI, and SRAI generate an illegal instruction exception if imm[5] 6= 0.

For example, the following three instructions have a shift amount of 32 and are decoded as illegal instructions for RV32I.

0x02029313        slli    t1, t0, 0x20
0x0202d313        srli    t1, t0, 0x20
0x4202d313        srai    t1, t0, 0x20

Therefore, such instructions should raise an illegal instruction exception, but in the current RSD, such instructions are executed normally without raising an illegal instruction exception.

Steps to reproduce the issue

If you execute a code that embeds an invalid shift instruction like the code below, you can confirm that the illegal instruction executes normally without raising an illegal instruction exception.

int main(void){
    asm volatile (".byte 0x13, 0x93, 0x02, 0x02");
}