[clang] [NFC][-Wunsafe-buffer-usage] Refactor safe pattern check for pointer-size pairs (PR #145626)

[Ziqing Luo via cfe-commits]

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@@ -453,22 +453,108 @@ static bool areEqualIntegers(const Expr *E1, const Expr *E2, ASTContext &Ctx) {
   }
 }
 
+// Providing that `Ptr` is a pointer and `Size` is an unsigned-integral
+// expression, returns true iff they follow one of the following safe
+// patterns:
+//  1. Ptr is `DRE.data()` and Size is `DRE.size()`, where DRE is a hardened
+//     container or view;
+//
+//  2. Ptr is `a` and Size is `n`, where `a` is of an array-of-T with constant
+//     size `n`;
+//
+//  3. Ptr is `&var` and Size is `1`; or
+//     Ptr is `std::addressof(...)` and Size is `1`;
+//
+//  4. Size is `0`;
+static bool isPtrBufferSafe(const Expr *Ptr, const Expr *Size,
+                            ASTContext &Ctx) {
+  // Pattern 1:
+  if (auto *MCEPtr = dyn_cast<CXXMemberCallExpr>(Ptr->IgnoreParenImpCasts()))
+    if (auto *MCESize =
+            dyn_cast<CXXMemberCallExpr>(Size->IgnoreParenImpCasts())) {
+      auto *DREOfPtr = dyn_cast<DeclRefExpr>(
+          MCEPtr->getImplicitObjectArgument()->IgnoreParenImpCasts());
+      auto *DREOfSize = dyn_cast<DeclRefExpr>(
+          MCESize->getImplicitObjectArgument()->IgnoreParenImpCasts());
+
+      if (!DREOfPtr || !DREOfSize)
+        return false; // not in safe pattern
+      if (DREOfPtr->getDecl() != DREOfSize->getDecl())
+        return false;
+      if (MCEPtr->getMethodDecl()->getName() != "data")
+        return false;
+      // `MCEPtr->getRecordDecl()` must be non-null as `DREOfPtr` is non-null:
+      if (!MCEPtr->getRecordDecl()->isInStdNamespace())
+        return false;
+
+      auto *ObjII = MCEPtr->getRecordDecl()->getIdentifier();
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ziqingluo-90 wrote:

I guess it is possible that the standard library implementation uses any kind of anonymous records.

https://github.com/llvm/llvm-project/pull/145626