[analyzer] MallocChecker: Avoid redundant transitions.

Don't generate a checker-tagged node unconditionally on the first
checkDeadSymbols callback when no pointers are tracked.

This is a tiny performance optimization; it may change the behavior slightly
by making Static Analyzer bail out on max-nodes one node later (which is good)
but any test would either break for no good reason or become useless
every time someone sneezes.

Differential Revision: https://reviews.llvm.org/D54013

llvm-svn: 347955

clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp

@@ -2346,20 +2346,29 @@ void MallocChecker::checkDeadSymbols(SymbolReaper &SymReaper,
                                      CheckerContext &C) const
 {
   ProgramStateRef state = C.getState();
-  RegionStateTy RS = state->get<RegionState>();
+  RegionStateTy OldRS = state->get<RegionState>();
   RegionStateTy::Factory &F = state->get_context<RegionState>();
 
+  RegionStateTy RS = OldRS;
   SmallVector<SymbolRef, 2> Errors;
   for (RegionStateTy::iterator I = RS.begin(), E = RS.end(); I != E; ++I) {
     if (SymReaper.isDead(I->first)) {
       if (I->second.isAllocated() || I->second.isAllocatedOfSizeZero())
         Errors.push_back(I->first);
       // Remove the dead symbol from the map.
       RS = F.remove(RS, I->first);
-
     }
   }
 
+  if (RS == OldRS) {
+    // We shouldn't have touched other maps yet.
+    assert(state->get<ReallocPairs>() ==
+           C.getState()->get<ReallocPairs>());
+    assert(state->get<FreeReturnValue>() ==
+           C.getState()->get<FreeReturnValue>());
+    return;
+  }
+
   // Cleanup the Realloc Pairs Map.
   ReallocPairsTy RP = state->get<ReallocPairs>();
   for (ReallocPairsTy::iterator I = RP.begin(), E = RP.end(); I != E; ++I) {