[clang] [analyzer] Refine invalidation caused by `fread` (PR #93408)

[Arthur Eubanks via cfe-commits]

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@@ -907,6 +945,76 @@ void StreamChecker::preWrite(const FnDescription *Desc, const CallEvent &Call,
   C.addTransition(State);
 }
 
+static std::optional<QualType> getPointeeType(const MemRegion *R) {
+  if (!R)
+    return std::nullopt;
+  if (const auto *ER = dyn_cast<ElementRegion>(R))
+    return ER->getElementType();
+  if (const auto *TR = dyn_cast<TypedValueRegion>(R))
+    return TR->getValueType();
+  if (const auto *SR = dyn_cast<SymbolicRegion>(R))
+    return SR->getPointeeStaticType();
+  return std::nullopt;
+}
+
+static std::optional<NonLoc> getStartIndex(SValBuilder &SVB,
+                                           const MemRegion *R) {
+  if (!R)
+    return std::nullopt;
+
+  auto Zero = [&SVB] {
+    BasicValueFactory &BVF = SVB.getBasicValueFactory();
+    return nonloc::ConcreteInt(BVF.getIntValue(0, /*isUnsigned=*/false));
+  };
+
+  if (const auto *ER = dyn_cast<ElementRegion>(R))
+    return ER->getIndex();
+  if (const auto *TR = dyn_cast<TypedValueRegion>(R))
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aeubanks wrote:

unused variable (and ditto below), please use `isa<>`

https://github.com/llvm/llvm-project/pull/93408