ZJIT: Remove no-op movs after register allocation

Previously `no_dead_mov_from_vreg` generated:

    0x0: ldur x0, [x0]
    0x4: mov x0, x0
    0x8: ret

Because of phase ordering. Split couldn't recognize that the no-op mov
because at that point it sees a `VReg`.

zjit/src/backend/arm64/mod.rs

@@ -1424,6 +1424,20 @@ mod tests {
         ");
     }
 
+    #[test]
+    fn no_dead_mov_from_vreg() {
+        let (mut asm, mut cb) = setup_asm();
+
+        let ret_val = asm.load(Opnd::mem(64, C_RET_OPND, 0));
+        asm.cret(ret_val);
+
+        asm.compile_with_num_regs(&mut cb, 1);
+        assert_disasm!(cb, "000040f8c0035fd6", "
+            0x0: ldur x0, [x0]
+            0x4: ret
+        ");
+    }
+
     #[test]
     fn test_emit_add() {
         let (mut asm, mut cb) = setup_asm();

zjit/src/backend/lir.rs

@@ -1752,6 +1752,9 @@ impl Assembler
                         asm.push_insn(Insn::PosMarker(end_marker));
                     }
                 }
+                Insn::Mov { src, dest } | Insn::LoadInto { dest, opnd: src } if src == dest => {
+                    // Remove no-op move now that VReg are resolved to physical Reg
+                }
                 _ => asm.push_insn(insn),
             }