[analyzer] Fix StdLibraryFunctionsChecker performance issue

[vsavchenko]

Summary

initFunctionSummaries lazily initializes a data structure with
function summaries for standard library functions. It is called for
every pre-, post-, and eval-call events, i.e. 3 times for each call on
the path. If the initialization doesn't find any standard library
functions in the translation unit, it will get re-tried (with the same
effect) many times even for small translation units.

For projects not using standard libraries, the speed-up can reach 50%
after this patch.

[martong]

Good catch! Thank you!

[steakhal]

For projects not using standard libraries, the speed-up can reach 50% after this patch.

Uh, that's something serious!

clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp

class StdLibraryFunctionsChecker
   };
 
   // The map of all functions supported by the checker. It is initialized
   // lazily, and it doesn't change after initialization.
   using FunctionSummaryMapType = llvm::DenseMap<const FunctionDecl *, Summary>;
   mutable FunctionSummaryMapType FunctionSummaryMap;
 
   mutable std::unique_ptr<BugType> BT_InvalidArg;
+  mutable bool SummariesInitialized = false;
 
   static SVal getArgSVal(const CallEvent &Call, ArgNo ArgN) {
     return ArgN == Ret ? Call.getReturnValue() : Call.getArgSVal(ArgN);
   }
 
 public:
   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
   void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
StdLibraryFunctionsChecker::findFunctionSummary(const CallEvent &Call,
   const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
   if (!FD)
     return None;
   return findFunctionSummary(FD, C);
 }
 
 void StdLibraryFunctionsChecker::initFunctionSummaries(
     CheckerContext &C) const {
-  if (!FunctionSummaryMap.empty())
+  if (SummariesInitialized)
     return;
 
   SValBuilder &SVB = C.getSValBuilder();
   BasicValueFactory &BVF = SVB.getBasicValueFactory();
   const ASTContext &ACtx = BVF.getContext();
 
   // Helper class to lookup a type by its name.
   class LookupType {
addToFunctionSummaryMap(
             .ArgConstraint(BufferSize(/*Buffer=*/ArgNo(0),
                                       /*BufSize=*/BVF.getValue(10, IntTy))));
     addToFunctionSummaryMap(
         {"__test_restrict_param_0", "__test_restrict_param_1",
          "__test_restrict_param_2"},
         Signature(ArgTypes{VoidPtrRestrictTy}, RetType{VoidTy}),
         Summary(EvalCallAsPure));
   }
+
+  SummariesInitialized = true;
 }
 
 void ento::registerStdCLibraryFunctionsChecker(CheckerManager &mgr) {
   auto *Checker = mgr.registerChecker<StdLibraryFunctionsChecker>();
   Checker->DisplayLoadedSummaries =
       mgr.getAnalyzerOptions().getCheckerBooleanOption(
           Checker, "DisplayLoadedSummaries");
   Checker->ModelPOSIX =