add reprod examples for issues

reprod/13_external_loop_variable.core_desc

@@ -0,0 +1,23 @@
+// A loop variable defined beforehand does not work
+
+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 count = 0;
+                        unsigned int i = 0;
+                        for(i=0; i<=32; i++){
+                            count = 1;
+                        }
+                        X[rd] = count;
+                    }
+        }
+    }
+}