Add testcase for irreducible and extractLoops

Author: radumcostache

Test/extractloops/irreducibleExtract.bpl

@@ -0,0 +1,22 @@
+// RUN: %parallel-boogie -extractLoops "%s" > "%t"
+// RUN: %OutputCheck --file-to-check "%t" "%s"
+// CHECK-L: Boogie program verifier finished with 2 verified, 0 errors
+
+procedure {:entrypoint} simple_irreducible() {
+    var x: int;
+    x := 0;
+    A:
+        assume x == 0;
+        x := x + 1;
+        goto B, C;
+
+    B:
+        assume x <= 2;
+        x := x - 1;
+        goto C, D;
+    C: 
+        x := x + 1;
+        goto B;
+    D: 
+        assume x <= 1;
+}