[Analyzer] Fix errors in iterator modeling

There is major a bug found in iterator modeling: upon adding a value
to or subtracting a value from an iterator the position of the original
iterator is also changed beside the result. This patch fixes this bug.

To catch such bugs in the future we also changed the tests to look for
regular expressions including an end-of-line symbol (`$`) so we can
prevent false matches where only the tested prefix matches.

Another minor bug is that when printing the state, all the iterator
positions are printed in a single line. This patch also fixes this.

Differential Revision: https://reviews.llvm.org/D82385

clang/lib/StaticAnalyzer/Checkers/IteratorModeling.cpp

@@ -458,7 +458,7 @@ void IteratorModeling::processComparison(CheckerContext &C,
     StateTrue = StateTrue->assume(*ConditionVal, true);
     C.addTransition(StateTrue);
   }
-  
+
   if (auto StateFalse = relateSymbols(State, Sym1, Sym2, Op != OO_EqualEqual)) {
     StateFalse = StateFalse->assume(*ConditionVal, false);
     C.addTransition(StateFalse);
@@ -540,14 +540,16 @@ void IteratorModeling::handleRandomIncrOrDecr(CheckerContext &C,
 
   auto &TgtVal = (Op == OO_PlusEqual || Op == OO_MinusEqual) ? LHS : RetVal;
 
-  auto NewState =
-    advancePosition(State, LHS, Op, *value);
-  if (NewState) {
-    const auto *NewPos = getIteratorPosition(NewState, LHS);
+  // `AdvancedState` is a state where the position of `LHS` is advanced. We
+  // only need this state to retrieve the new position, but we do not want
+  // to change the position of `LHS` (in every case).
+  auto AdvancedState = advancePosition(State, LHS, Op, *value);
+  if (AdvancedState) {
+    const auto *NewPos = getIteratorPosition(AdvancedState, LHS);
     assert(NewPos &&
            "Iterator should have position after successful advancement");
 
-    State = setIteratorPosition(NewState, TgtVal, *NewPos);
+    State = setIteratorPosition(State, TgtVal, *NewPos);
     C.addTransition(State);
   } else {
     assignToContainer(C, CE, TgtVal, Pos->getContainer());
@@ -611,10 +613,15 @@ void IteratorModeling::printState(raw_ostream &Out, ProgramStateRef State,
                                   const char *NL, const char *Sep) const {
   auto SymbolMap = State->get<IteratorSymbolMap>();
   auto RegionMap = State->get<IteratorRegionMap>();
+  // Use a counter to add newlines before every line except the first one.
+  unsigned Count = 0;
 
   if (!SymbolMap.isEmpty() || !RegionMap.isEmpty()) {
     Out << Sep << "Iterator Positions :" << NL;
     for (const auto &Sym : SymbolMap) {
+      if (Count++)
+        Out << NL;
+
       Sym.first->dumpToStream(Out);
       Out << " : ";
       const auto Pos = Sym.second;
@@ -625,6 +632,9 @@ void IteratorModeling::printState(raw_ostream &Out, ProgramStateRef State,
     }
 
     for (const auto &Reg : RegionMap) {
+      if (Count++)
+        Out << NL;
+
       Reg.first->dumpToStream(Out);
       Out << " : ";
       const auto Pos = Reg.second;