[analyzer] Don't track the condition of foreach loops

[Szelethus]

Summary

As discussed on the mailing list, notes originating from the tracking of foreach loop conditions are always meaningless.

[NoQ]

Do it! 8)

clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp

PathDiagnosticPieceRef TrackControlDependencyCondBRVisitor::VisitNode(
   // TODO: Cache CFGBlocks for each ExplodedNode.
   if (!OriginB || !NB)
     return nullptr;
 
   if (isAssertlikeBlock(NB, BRC.getASTContext()))
     return nullptr;
 
   if (ControlDeps.isControlDependent(OriginB, NB)) {
+    // We don't really want to explain for range loops. Evidence suggests that
+    // the only thing that leads to is the addition of calls to operator!=.
+    if (isa<CXXForRangeStmt>(NB->getTerminator()))
+      return nullptr;
+
     if (const Expr *Condition = NB->getLastCondition()) {
       // Keeping track of the already tracked conditions on a visitor level
       // isn't sufficient, because a new visitor is created for each tracked
       // expression, hence the BugReport level set.
       if (BR.addTrackedCondition(N)) {
         bugreporter::trackExpressionValue(
             N, Condition, BR, bugreporter::TrackingKind::Condition,
             /*EnableNullFPSuppression=*/false);

clang/test/Analysis/track-control-dependency-conditions.cpp

void f() {
   if (y) // expected-note{{Assuming 'y' is not equal to 0}}
          // expected-note@-1{{Taking true branch}}
          // debug-note@-2{{Tracking condition 'y'}}
     *x = 5; // expected-warning{{Dereference of null pointer}}
             // expected-note@-1{{Dereference of null pointer}}
 }
 } // end of namespace condition_written_in_nested_stackframe_before_assignment
 
+namespace dont_explain_foreach_loops {
+
+struct Iterator {
+  int *pos;
+  bool operator!=(Iterator other) const {
+    return pos && other.pos && pos != other.pos;
+  }
+  int operator*();
+  Iterator operator++();
+};
+
+struct Container {
+  Iterator begin();
+  Iterator end();
+};
+
+void f(Container Cont) {
+  int flag = 0;
+  int *x = 0; // expected-note{{'x' initialized to a null pointer value}}
+  for (int i : Cont)
+    if (i) // expected-note   {{Assuming 'i' is not equal to 0}}
+           // expected-note@-1{{Taking true branch}}
+           // debug-note@-2{{Tracking condition 'i'}}
+      flag = i;
+
+  if (flag) // expected-note{{'flag' is not equal to 0}}
+            // expected-note@-1{{Taking true branch}}
+            // debug-note@-2{{Tracking condition 'flag'}}
+    *x = 5; // expected-warning{{Dereference of null pointer}}
+            // expected-note@-1{{Dereference of null pointer}}
+}
+
+} // end of namespace dont_explain_foreach_loops
+
 namespace collapse_point_not_in_condition_bool {
 
 [[noreturn]] void halt();
 
 void check(bool b) {
   if (!b) // tracking-note{{Assuming 'b' is true, which will be (a part of a) condition}}
           // tracking-note@-1{{Taking false branch}}
     halt();