Dataflow: update fieldFlowBranchLimit semantics

cpp/ql/lib/semmle/code/cpp/dataflow/internal/DataFlowPrivate.qll

@@ -290,6 +290,8 @@ predicate knownSourceModel(Node source, string model) { none() }
 
 predicate knownSinkModel(Node sink, string model) { none() }
 
+class DataFlowSecondLevelScope = Unit;
+
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a
  * side-effect, resulting in a summary from `p` to itself.

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

@@ -22,6 +22,8 @@ module CppDataFlow implements InputSig<Location> {
 
   predicate getAdditionalFlowIntoCallNodeTerm = Private::getAdditionalFlowIntoCallNodeTerm/2;
 
+  predicate getSecondLevelScope = Private::getSecondLevelScope/1;
+
   predicate validParameterAliasStep = Private::validParameterAliasStep/2;
 
   predicate mayBenefitFromCallContext = Private::mayBenefitFromCallContext/1;

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

@@ -1263,3 +1263,74 @@ predicate validParameterAliasStep(Node node1, Node node2) {
     )
   )
 }
+
+private predicate isTopLevel(Cpp::Stmt s) { any(Function f).getBlock().getAStmt() = s }
+
+private Cpp::Stmt getAChainedBranch(Cpp::IfStmt s) {
+  result = s.getThen()
+  or
+  exists(Cpp::Stmt elseBranch | s.getElse() = elseBranch |
+    result = getAChainedBranch(elseBranch)
+    or
+    result = elseBranch and not elseBranch instanceof Cpp::IfStmt
+  )
+}
+
+private Instruction getInstruction(Node n) {
+  result = n.asInstruction() or
+  result = n.asOperand().getUse() or
+  result = n.(SsaPhiNode).getPhiNode().getBasicBlock().getFirstInstruction() or
+  n.(IndirectInstruction).hasInstructionAndIndirectionIndex(result, _) or
+  result = getInstruction(n.(PostUpdateNode).getPreUpdateNode())
+}
+
+private newtype TDataFlowSecondLevelScope =
+  TTopLevelIfBranch(Cpp::Stmt s) {
+    exists(Cpp::IfStmt ifstmt | s = getAChainedBranch(ifstmt) and isTopLevel(ifstmt))
+  } or
+  TTopLevelSwitchCase(Cpp::SwitchCase s) {
+    exists(Cpp::SwitchStmt switchstmt | s = switchstmt.getASwitchCase() and isTopLevel(switchstmt))
+  }
+
+/**
+ * A second-level control-flow scope in a `switch` or a chained `if` statement.
+ *
+ * This is a `switch` case or a branch of a chained `if` statement, given that
+ * the `switch` or `if` statement is top level, that is, it is not nested inside
+ * other CFG constructs.
+ */
+class DataFlowSecondLevelScope extends TDataFlowSecondLevelScope {
+  /** Gets a textual representation of this element. */
+  string toString() {
+    exists(Cpp::Stmt s | this = TTopLevelIfBranch(s) | result = s.toString())
+    or
+    exists(Cpp::SwitchCase s | this = TTopLevelSwitchCase(s) | result = s.toString())
+  }
+
+  /** Gets the primary location of this element. */
+  Cpp::Location getLocation() {
+    exists(Cpp::Stmt s | this = TTopLevelIfBranch(s) | result = s.getLocation())
+    or
+    exists(Cpp::SwitchCase s | this = TTopLevelSwitchCase(s) | result = s.getLocation())
+  }
+
+  /**
+   * Gets a statement directly contained in this scope. For an `if` branch, this
+   * is the branch itself, and for a `switch case`, this is one the statements
+   * of that case branch.
+   */
+  private Cpp::Stmt getAStmt() {
+    exists(Cpp::Stmt s | this = TTopLevelIfBranch(s) | result = s)
+    or
+    exists(Cpp::SwitchCase s | this = TTopLevelSwitchCase(s) | result = s.getAStmt())
+  }
+
+  /** Gets a data-flow node nested within this scope. */
+  Node getANode() {
+    getInstruction(result).getAst().(Cpp::ControlFlowNode).getEnclosingStmt().getParentStmt*() =
+      this.getAStmt()
+  }
+}
+
+/** Gets the second-level scope containing the node `n`, if any. */
+DataFlowSecondLevelScope getSecondLevelScope(Node n) { result.getANode() = n }

cpp/ql/test/library-tests/dataflow/taint-tests/swap2.cpp

@@ -84,7 +84,7 @@ void test_copy_assignment_operator()
 
     swap(z1, z2);
 
-    sink(z2.data1); // $ ir MISSING: ast
+    sink(z2.data1); // $ ir ast
     sink(z1.data1); // $ SPURIOUS: ir ast=81:27 ast=82:16
 }
 

csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll

@@ -2882,6 +2882,8 @@ predicate knownSourceModel(Node source, string model) { sourceNode(source, _, mo
 
 predicate knownSinkModel(Node sink, string model) { sinkNode(sink, _, model) }
 
+class DataFlowSecondLevelScope = Unit;
+
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a
  * side-effect, resulting in a summary from `p` to itself.

csharp/ql/test/library-tests/dataflow/collections/CollectionFlow.ql

@@ -14,8 +14,6 @@ module ArrayFlowConfig implements DataFlow::ConfigSig {
       mc.getAnArgument() = sink.asExpr()
     )
   }
-
-  int fieldFlowBranchLimit() { result = 100 }
 }
 
 module ArrayFlow = DataFlow::Global<ArrayFlowConfig>;

csharp/ql/test/library-tests/dataflow/types/Types.ql

@@ -18,8 +18,6 @@ module TypesConfig implements DataFlow::ConfigSig {
       mc.getAnArgument() = sink.asExpr()
     )
   }
-
-  int fieldFlowBranchLimit() { result = 1000 }
 }
 
 import ValueFlowTest<TypesConfig>

go/ql/lib/semmle/go/dataflow/internal/DataFlowPrivate.qll

@@ -415,6 +415,8 @@ predicate knownSourceModel(Node source, string model) { sourceNode(source, _, mo
 
 predicate knownSinkModel(Node sink, string model) { sinkNode(sink, _, model) }
 
+class DataFlowSecondLevelScope = Unit;
+
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a
  * side-effect, resulting in a summary from `p` to itself.

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowImplSpecific.qll

@@ -20,6 +20,8 @@ module JavaDataFlow implements InputSig<Location> {
 
   Node exprNode(DataFlowExpr e) { result = Public::exprNode(e) }
 
+  predicate getSecondLevelScope = Private::getSecondLevelScope/1;
+
   predicate mayBenefitFromCallContext = Private::mayBenefitFromCallContext/1;
 
   predicate viableImplInCallContext = Private::viableImplInCallContext/2;

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowPrivate.qll

@@ -581,6 +581,81 @@ predicate knownSourceModel(Node source, string model) { sourceNode(source, _, mo
 
 predicate knownSinkModel(Node sink, string model) { sinkNode(sink, _, model) }
 
+private predicate isTopLevel(Stmt s) {
+  any(Callable c).getBody() = s
+  or
+  exists(BlockStmt b | s = b.getAStmt() and isTopLevel(b))
+}
+
+private Stmt getAChainedBranch(IfStmt s) {
+  result = s.getThen()
+  or
+  exists(Stmt elseBranch | s.getElse() = elseBranch |
+    result = getAChainedBranch(elseBranch)
+    or
+    result = elseBranch and not elseBranch instanceof IfStmt
+  )
+}
+
+private newtype TDataFlowSecondLevelScope =
+  TTopLevelIfBranch(Stmt s) {
+    exists(IfStmt ifstmt | s = getAChainedBranch(ifstmt) and isTopLevel(ifstmt))
+  } or
+  TTopLevelSwitchCase(SwitchCase s) {
+    exists(SwitchStmt switchstmt | s = switchstmt.getACase() and isTopLevel(switchstmt))
+  }
+
+private SwitchCase getPrecedingCase(Stmt s) {
+  result = s
+  or
+  exists(SwitchStmt switch, int i |
+    s = switch.getStmt(i) and
+    not s instanceof SwitchCase and
+    result = getPrecedingCase(switch.getStmt(i - 1))
+  )
+}
+
+/**
+ * A second-level control-flow scope in a `switch` or a chained `if` statement.
+ *
+ * This is a `switch` case or a branch of a chained `if` statement, given that
+ * the `switch` or `if` statement is top level, that is, it is not nested inside
+ * other CFG constructs.
+ */
+class DataFlowSecondLevelScope extends TDataFlowSecondLevelScope {
+  /** Gets a textual representation of this element. */
+  string toString() {
+    exists(Stmt s | this = TTopLevelIfBranch(s) | result = s.toString())
+    or
+    exists(SwitchCase s | this = TTopLevelSwitchCase(s) | result = s.toString())
+  }
+
+  /**
+   * Gets a statement directly contained in this scope. For an `if` branch, this
+   * is the branch itself, and for a `switch case`, this is one the statements
+   * of that case branch.
+   */
+  private Stmt getAStmt() {
+    exists(Stmt s | this = TTopLevelIfBranch(s) | result = s)
+    or
+    exists(SwitchCase s | this = TTopLevelSwitchCase(s) |
+      result = s.getRuleStatement() or
+      s = getPrecedingCase(result)
+    )
+  }
+
+  /** Gets a data-flow node nested within this scope. */
+  Node getANode() { getRelatedExpr(result).getAnEnclosingStmt() = this.getAStmt() }
+}
+
+private Expr getRelatedExpr(Node n) {
+  n.asExpr() = result or
+  n.(PostUpdateNode).getPreUpdateNode().asExpr() = result
+}
+
+/** Gets the second-level scope containing the node `n`, if any. */
+DataFlowSecondLevelScope getSecondLevelScope(Node n) { result.getANode() = n }
+
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a
  * side-effect, resulting in a summary from `p` to itself.

java/ql/test/library-tests/frameworks/guava/handwritten/flow.ql

@@ -18,8 +18,6 @@ module ValueFlowConfig implements DataFlow::ConfigSig {
   predicate isSink(DataFlow::Node n) {
     exists(MethodCall ma | ma.getMethod().hasName("sink") | n.asExpr() = ma.getAnArgument())
   }
-
-  int fieldFlowBranchLimit() { result = 100 }
 }
 
 module ValueFlow = DataFlow::Global<ValueFlowConfig>;

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPrivate.qll

@@ -1087,6 +1087,8 @@ predicate knownSinkModel(Node sink, string model) {
   sink = ModelOutput::getASinkNode(_, model).asSink()
 }
 
+class DataFlowSecondLevelScope = Unit;
+
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a
  * side-effect, resulting in a summary from `p` to itself.

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPrivate.qll

@@ -2254,6 +2254,8 @@ predicate knownSinkModel(Node sink, string model) {
   sink = ModelOutput::getASinkNode(_, model).asSink()
 }
 
+class DataFlowSecondLevelScope = Unit;
+
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a
  * side-effect, resulting in a summary from `p` to itself.

shared/dataflow/change-notes/2024-04-19-fieldflowbranchlimit.md

@@ -0,0 +1,4 @@
+---
+category: majorAnalysis
+---
+* The data flow library performs heuristic filtering of code paths that have a high degree of control-flow uncertainty for improved performance in cases that are deemed unlikely to yield true positive flow paths. This filtering can be controlled with the `fieldFlowBranchLimit` predicate in configurations. Two bugs have been fixed in relation to this: Some cases of high uncertainty were not being correctly identified. This fix improves performance in certain scenarios. Another group of cases of low uncertainty were also being misidentified, which led to false negatives. Taken together, we generally expect some additional query results with more true positives and fewer false positives.

shared/dataflow/codeql/dataflow/DataFlow.qll

@@ -308,6 +308,24 @@ signature module InputSig<LocationSig Location> {
    */
   default int getAdditionalFlowIntoCallNodeTerm(ArgumentNode arg, ParameterNode p) { none() }
 
+  /**
+   * A second-level control-flow scope in a callable.
+   *
+   * This is used to provide a more fine-grained separation of a callable
+   * context for the purpose of identifying uncertain control flow. For most
+   * languages, this is not needed, as this separation is handled through
+   * virtual dispatch, but for some cases (for example, C++) this can be used to
+   * identify, for example, large top-level switch statements acting like
+   * virtual dispatch.
+   */
+  class DataFlowSecondLevelScope {
+    /** Gets a textual representation of this element. */
+    string toString();
+  }
+
+  /** Gets the second-level scope containing the node `n`, if any. */
+  default DataFlowSecondLevelScope getSecondLevelScope(Node n) { none() }
+
   bindingset[call, p, arg]
   default predicate golangSpecificParamArgFilter(
     DataFlowCall call, ParameterNode p, ArgumentNode arg