Merge pull request #1437 from jbj/bb-shortestDistances

C++: use shortestDistances in PrimitiveBasicBlocks

cpp/ql/src/semmle/code/cpp/controlflow/internal/PrimitiveBasicBlocks.qll

@@ -60,27 +60,14 @@ private cached module Cached {
     not n2 instanceof PrimitiveBasicBlock
   }
 
-  /** Returns the index of `node` in its `PrimitiveBasicBlock`. */
-  private int getMemberIndex(Node node) {
-    primitive_basic_block_entry_node(node) and
-    result = 0
-    or
-    exists(Node prev |
-      member_step(prev, node) and
-      result = getMemberIndex(prev) + 1
-    )
-  }
-
   /** Holds if `node` is the `pos`th control-flow node in primitive basic block `bb`. */
   cached
   predicate primitive_basic_block_member(Node node, PrimitiveBasicBlock bb, int pos) {
-    primitive_basic_block_entry_node(bb) and
-    (
-      pos = 0 and
-      node = bb
-      or
-      pos = getMemberIndex(node) and
-      member_step+(bb, node)
+    primitive_basic_block_entry_node(bb) and node = bb and pos = 0
+    or
+    exists(Node prev |
+      member_step(prev, node) and
+      primitive_basic_block_member(prev, bb, pos - 1)
     )
   }