Data flow: Add precise call contexts to stage 2

Author: hvitved

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

@@ -923,28 +923,29 @@ private module Stage2 {
 
   ApOption apSome(Ap ap) { result = TBooleanSome(ap) }
 
-  class Cc = boolean;
-
-  class CcCall extends Cc {
-    CcCall() { this = true }
+  class Cc = CallContext;
 
-    /** Holds if this call context may be `call`. */
-    predicate matchesCall(DataFlowCall call) { any() }
-  }
+  class CcCall = CallContextCall;
 
-  class CcNoCall extends Cc {
-    CcNoCall() { this = false }
-  }
+  class CcNoCall = CallContextNoCall;
 
-  Cc ccNone() { result = false }
+  Cc ccNone() { result instanceof CallContextAny }
 
   private class LocalCc = Unit;
 
   bindingset[call, c, outercc]
-  private CcCall getCallContextCall(DataFlowCall call, DataFlowCallable c, Cc outercc) { any() }
+  private CcCall getCallContextCall(DataFlowCall call, DataFlowCallable c, Cc outercc) {
+    checkCallContextCall(outercc, call, c) and
+    if recordDataFlowCallSiteDispatch(call, c)
+    then result = TSpecificCall(call)
+    else result = TSomeCall()
+  }
 
   bindingset[call, c, innercc]
-  private CcNoCall getCallContextReturn(DataFlowCallable c, DataFlowCall call, Cc innercc) { any() }
+  private CcNoCall getCallContextReturn(DataFlowCallable c, DataFlowCall call, Cc innercc) {
+    checkCallContextReturn(innercc, c, call) and
+    if reducedViableImplInReturn(c, call) then result = TReturn(c, call) else result = ccNone()
+  }
 
   bindingset[node, cc, config]
   private LocalCc getLocalCc(NodeEx node, Cc cc, Configuration config) { any() }
@@ -2117,7 +2118,7 @@ private module Stage3 {
 private predicate flowCandSummaryCtx(NodeEx node, AccessPathFront argApf, Configuration config) {
   exists(AccessPathFront apf |
     Stage3::revFlow(node, true, _, apf, config) and
-    Stage3::fwdFlow(node, true, TAccessPathFrontSome(argApf), apf, config)
+    Stage3::fwdFlow(node, any(Stage3::CcCall ccc), TAccessPathFrontSome(argApf), apf, config)
   )
 }
 

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

@@ -786,13 +786,18 @@ private module Cached {
   }
 
   /**
-   * Holds if the call context `call` either improves virtual dispatch in
-   * `callable` or if it allows us to prune unreachable nodes in `callable`.
+   * Holds if the call context `call` improves virtual dispatch in `callable`.
    */
   cached
-  predicate recordDataFlowCallSite(DataFlowCall call, DataFlowCallable callable) {
+  predicate recordDataFlowCallSiteDispatch(DataFlowCall call, DataFlowCallable callable) {
     reducedViableImplInCallContext(_, callable, call)
-    or
+  }
+
+  /**
+   * Holds if the call context `call` allows us to prune unreachable nodes in `callable`.
+   */
+  cached
+  predicate recordDataFlowCallSiteUnreachable(DataFlowCall call, DataFlowCallable callable) {
     exists(Node n | getNodeEnclosingCallable(n) = callable | isUnreachableInCallCached(n, call))
   }
 
@@ -846,6 +851,15 @@ private module Cached {
     TAccessPathFrontSome(AccessPathFront apf)
 }
 
+/**
+ * Holds if the call context `call` either improves virtual dispatch in
+ * `callable` or if it allows us to prune unreachable nodes in `callable`.
+ */
+predicate recordDataFlowCallSite(DataFlowCall call, DataFlowCallable callable) {
+  recordDataFlowCallSiteDispatch(call, callable) or
+  recordDataFlowCallSiteUnreachable(call, callable)
+}
+
 /**
  * A `Node` at which a cast can occur such that the type should be checked.
  */