add reprod examples for issues

reprod/2_unsigned_subtract.core_desc

@@ -0,0 +1,20 @@
+// When substracting from an unsigned value, the result cannot auto-cast to the same unsigned type (e.g. "value of UI<32> - 1" gives a SI<33>, cannot be cast to UI<32>)
+
+InstructionSet Zbb {
+    architectural_state {
+        unsigned int XLEN=32;
+        const register unsigned<32> XLEN_R = 32;
+        register unsigned<XLEN> X[32] [[is_main_reg]];
+    }
+    instructions {
+        TEST {
+            encoding: 12'b011000000000 :: rs1[4:0] :: 3'b001 :: rd[4:0] :: 7'b0010011;
+            assembly: "{name(rd)}, {name(rs1)}";
+            behavior: {
+                        unsigned int test = XLEN_R - 1;
+                        //unsigned int test = (unsigned int)(XLEN_R - 1);
+                        X[rd] = test;
+                    }
+        }
+    }
+}