Remove Ecall and Ebreak from Instr

The ECALL and EBREAK instructions have distinct mcause values and are not considered illegal instructions. Since they trigger different types of traps, they do not require decoding in our decoder for illegal instructions. As a result, we can safely remove them from the instruction decoder.

src/decoder.rs

@@ -7,8 +7,6 @@ const OPCODE_MASK: usize = 0b1111111;
 /// A RISC-V instruction.
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Instr {
-    Ecall,
-    Ebreak,
     Wfi,
     /// CSR Read/Write
     Csrrw {
@@ -112,8 +110,6 @@ impl MiralisContext {
         let func7 = (raw >> 25) & 0b1111111;
         if func3 == 0b000 {
             return match imm {
-                0b000000000000 => Instr::Ecall,
-                0b000000000001 => Instr::Ebreak,
                 0b000100000101 => Instr::Wfi,
                 0b001100000010 => Instr::Mret,
                 0b000100000010 => Instr::Sret,
@@ -876,10 +872,6 @@ mod tests {
     #[test]
     fn system_instructions() {
         let mctx = MiralisContext::new(unsafe { Arch::detect_hardware() }, 0x100000, 0x2000);
-        // ECALL: Environment call.
-        assert_eq!(mctx.decode_system(0x00000073), Instr::Ecall);
-        // EBREAK: Environment break.
-        assert_eq!(mctx.decode_system(0x00100073), Instr::Ebreak);
         // MRET: Return from machine mode.
         assert_eq!(mctx.decode_system(0x30200073), Instr::Mret);
         // SRET: Return from supervisor mode.