[clang] [analyzer] Refactor recognition of the errno getter functions (PR #91531)

[Balázs Kéri via cfe-commits]

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@@ -136,53 +100,48 @@ void ErrnoModeling::checkBeginFunction(CheckerContext &C) const {
   ASTContext &ACtx = C.getASTContext();
   ProgramStateRef State = C.getState();
 
-  if (const auto *ErrnoVar = dyn_cast_or_null<VarDecl>(ErrnoDecl)) {
-    // There is an external 'errno' variable.
-    // Use its memory region.
-    // The memory region for an 'errno'-like variable is allocated in system
-    // space by MemRegionManager.
-    const MemRegion *ErrnoR =
-        State->getRegion(ErrnoVar, C.getLocationContext());
+  const MemRegion *ErrnoR;
+
+  if (ErrnoDecl) {
+    // There is an external 'errno' variable, so we can simply use the memory
+    // region that's associated with it.
+    ErrnoR = State->getRegion(ErrnoDecl, C.getLocationContext());
     assert(ErrnoR && "Memory region should exist for the 'errno' variable.");
-    State = State->set<ErrnoRegion>(ErrnoR);
-    State =
-        errno_modeling::setErrnoValue(State, C, 0, errno_modeling::Irrelevant);
-    C.addTransition(State);
-  } else if (ErrnoDecl) {
-    assert(isa<FunctionDecl>(ErrnoDecl) && "Invalid errno location function.");
-    // There is a function that returns the location of 'errno'.
-    // We must create a memory region for it in system space.
-    // Currently a symbolic region is used with an artifical symbol.
-    // FIXME: It is better to have a custom (new) kind of MemRegion for such
-    // cases.
+  } else {
+    // The 'errno' location is accessed via an internal getter function, so
+    // create a new symbolic memory region that can be used as the return value
+    // of that function.
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balazske wrote:

We should mention that this case happens even if there is no errno getter function at all

https://github.com/llvm/llvm-project/pull/91531