[clang] [-Wunsafe-buffer-usage] Ignore constant safe indices in array subscripts (PR #80504)

[Artem Dergachev via cfe-commits]

================
@@ -406,6 +406,39 @@ AST_MATCHER(CXXConstructExpr, isSafeSpanTwoParamConstruct) {
   }
   return false;
 }
+
+AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
+  // FIXME: Proper solution:
+  //  - refactor Sema::CheckArrayAccess
+  //    - split safe/OOB/unknown decision logic from diagnostics emitting code
+  //    -  e. g. "Try harder to find a NamedDecl to point at in the note."
+  //    already duplicated
+  //  - call both from Sema and from here
+
+  const DeclRefExpr *BaseDRE =
+      dyn_cast_or_null<DeclRefExpr>(Node.getBase()->IgnoreParenImpCasts());
----------------
haoNoQ wrote:

I don't think `IgnoreParenImpCasts()` can ever return null.
```suggestion
  const auto *BaseDRE =
      dyn_cast<DeclRefExpr>(Node.getBase()->IgnoreParenImpCasts());
```

https://github.com/llvm/llvm-project/pull/80504