Handle unreachable blocks in IR printing

Unreachable basic blocks are now assigned a large distance to ensure they are sorted last. Additionally, blocks without an order are labeled as 'Block (unordered)' to improve clarity in IR output.

Changes are attempt to fix instances of `(no string representation)` in output

Author: gfs

binary/ql/lib/semmle/code/binary/ast/ir/PrintIR.ql

@@ -103,12 +103,17 @@ private int getBlockOrderingInFunction(Function f, BasicBlock bb) {
   bb =
     rank[result + 1](BasicBlock bb2, string s, int d |
       bb2.getEnclosingFunction() = f and
-      d = distanceFromEntry(f.getEntryBlock(), bb2) and
+      (
+        d = distanceFromEntry(f.getEntryBlock(), bb2)
+        or
+        // Unreachable blocks get a large distance so they sort last
+        not exists(distanceFromEntry(f.getEntryBlock(), bb2)) and d = 999999
+      ) and
       s =
-        strictconcat(int i, string instr |
+        concat(int i, string instr |
           instr = bb2.getNode(i).asInstruction().toString()
         |
-          instr order by i
+          instr, "" order by i
         )
     |
       bb2 order by d, s
@@ -134,7 +139,12 @@ private class PrintableIRBlock extends PrintableNode, TPrintableBasicBlock {
 
   override Location getLocation() { result = block.getLocation() }
 
-  override string getLabel() { result = "Block " + this.getOrder() }
+  override string getLabel() {
+    result = "Block " + this.getOrder()
+    or
+    not exists(this.getOrder()) and
+    result = "Block (unordered)"
+  }
 
   override int getOrder() { result = getBlockIndex(block) }