C++: Don't do indirect (instruction -> operand) flow when there's a store to the address in between the instruction and the operand.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -1520,6 +1520,25 @@ private module Cached {
     )
   }
 
+  /**
+   * Holds if `operand.getDef() = instr`, but there exists a `StoreInstruction` that
+   * writes to an address that is equivalent to the value computed by `instr` in
+   * between `instr` and `operand`, and therefore there should not be flow from `*instr`
+   * to `*operand`.
+   */
+  pragma[nomagic]
+  private predicate isStoredToBetween(Instruction instr, Operand operand) {
+    simpleOperandLocalFlowStep(pragma[only_bind_into](instr), pragma[only_bind_into](operand)) and
+    exists(StoreInstruction store, IRBlock block, int storeIndex, int instrIndex, int operandIndex |
+      store.getDestinationAddress() = instr and
+      block.getInstruction(storeIndex) = store and
+      block.getInstruction(instrIndex) = instr and
+      block.getInstruction(operandIndex) = operand.getUse() and
+      instrIndex < storeIndex and
+      storeIndex < operandIndex
+    )
+  }
+
   private predicate indirectionInstructionFlow(
     RawIndirectInstruction nodeFrom, IndirectOperand nodeTo
   ) {
@@ -1529,7 +1548,8 @@ private module Cached {
       simpleOperandLocalFlowStep(pragma[only_bind_into](instr), pragma[only_bind_into](operand))
     |
       hasOperandAndIndex(nodeTo, operand, pragma[only_bind_into](indirectionIndex)) and
-      hasInstructionAndIndex(nodeFrom, instr, pragma[only_bind_into](indirectionIndex))
+      hasInstructionAndIndex(nodeFrom, instr, pragma[only_bind_into](indirectionIndex)) and
+      not isStoredToBetween(instr, operand)
     )
   }