C++: Prune the set of interesting pointer-arithmetic instructions by another flow.

cpp/ql/src/experimental/Security/CWE/CWE-193/InvalidPointerDeref.ql

@@ -241,6 +241,7 @@ pragma[nomagic]
 predicate pointerAddInstructionHasBounds(
   PointerAddInstruction pai, DataFlow::Node sink1, DataFlow::Node sink2, int delta
 ) {
+  InterestingPointerAddInstruction::isInteresting(pragma[only_bind_into](pai)) and
   exists(Instruction right, Instruction instr2 |
     pai.getRight() = right and
     pai.getLeft() = sink1.asInstruction() and
@@ -251,6 +252,29 @@ predicate pointerAddInstructionHasBounds(
   )
 }
 
+module InterestingPointerAddInstruction {
+  private module PointerAddInstructionConfig implements DataFlow::ConfigSig {
+    predicate isSource(DataFlow::Node source) {
+      // The sources is the same as in the sources for the second
+      // projection in the `AllocToInvalidPointerConfig` module.
+      hasSize(source.asConvertedExpr(), _, _)
+    }
+
+    predicate isSink(DataFlow::Node sink) {
+      sink.asInstruction() = any(PointerAddInstruction pai).getLeft()
+    }
+  }
+
+  private import DataFlow::Global<PointerAddInstructionConfig>
+
+  predicate isInteresting(PointerAddInstruction pai) {
+    exists(DataFlow::Node n |
+      n.asInstruction() = pai.getLeft() and
+      flowTo(n)
+    )
+  }
+}
+
 /**
  * Holds if `pai` is non-strictly upper bounded by `sink2 + delta` and `sink1` is the
  * left operand of the pointer-arithmetic operation.