[clang][dataflow] Simplify implementation of `transferStdForwardCall()` in optional check.

[mboehme]

Summary

The argument and return value of std::forward is always a reference, so we can simply forward the storage location.

Depends On D155075

[gribozavr2]

clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp

686–687

Should we add an assert that it is not a value?

[mboehme]

clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp

686–687

getStorageLocationStrict already contains such an assertion.

clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp

auto *Arg1Loc = cast_or_null<AggregateStorageLocation>(
       State.Env.getStorageLocationStrict(*E->getArg(1)));
   transferSwap(Arg0Loc, Arg1Loc, State.Env);
 }
 
 void transferStdForwardCall(const CallExpr *E, const MatchFinder::MatchResult &,
                             LatticeTransferState &State) {
   assert(E->getNumArgs() == 1);
 
-  StorageLocation *LocRet = State.Env.getStorageLocation(*E, SkipPast::None);
-  if (LocRet != nullptr)
-    return;
-
-  StorageLocation *LocArg =
-      State.Env.getStorageLocation(*E->getArg(0), SkipPast::Reference);
-
-  if (LocArg == nullptr)
-    return;
-
-  Value *ValArg = State.Env.getValue(*LocArg);
-  if (ValArg == nullptr)
-    ValArg = &createOptionalValue(State.Env.makeAtomicBoolValue(), State.Env);
-
-  // Create a new storage location
-  LocRet = &State.Env.createStorageLocation(*E);
-  State.Env.setStorageLocation(*E, *LocRet);
-
-  State.Env.setValue(*LocRet, *ValArg);
+  if (auto *Loc = State.Env.getStorageLocationStrict(*E->getArg(0)))
+    State.Env.setStorageLocationStrict(*E, *Loc);
 }
 
 const Formula &evaluateEquality(Arena &A, const Formula &EqVal,
                                 const Formula &LHS, const Formula &RHS) {
   // Logically, an optional<T> object is composed of two values - a `has_value`
   // bit and a value of type T. Equality of optional objects compares both
   // values. Therefore, merely comparing the `has_value` bits isn't sufficient:
   // when two optional objects are engaged, the equality of their respective