[Clang][AST] Fix crash in APValue::LValueBase::getType when we have invalid decl

In some cases when calling APValue::LValueBase::getType() when we have a
ValueDecl in some cases we don't handle invalid decls. We iterating over
redeclarations we reset the current decl to the current most recent decl and
we check the next redeclaration to ensure it is not invalid.

Fixes: #69468

Author: shafik

clang/docs/ReleaseNotes.rst

@@ -641,6 +641,10 @@ Bug Fixes in This Version
   Fixes (`#67317 <https://github.com/llvm/llvm-project/issues/67317>`_)
 - Clang now properly diagnoses use of stand-alone OpenMP directives after a
   label (including ``case`` or ``default`` labels).
+- Fix crash when dealing with ill-formed code where we were not handling invalid
+  redeclarations properly.
+  Fixes (`#69468 <https://github.com/llvm/llvm-project/issues/69468>`_)
+
 
   Before:
 

clang/lib/AST/APValue.cpp

@@ -70,11 +70,13 @@ QualType APValue::LValueBase::getType() const {
     // constexpr int *p = &arr[1]; // valid?
     //
     // For now, we take the most complete type we can find.
-    for (auto *Redecl = cast<ValueDecl>(D->getMostRecentDecl()); Redecl;
+    for (auto *Redecl = cast<ValueDecl>(D->getMostRecentDecl());
+         Redecl && !Redecl->isInvalidDecl();
          Redecl = cast_or_null<ValueDecl>(Redecl->getPreviousDecl())) {
       QualType T = Redecl->getType();
       if (!T->isIncompleteArrayType())
         return T;
+      D = Redecl;
     }
     return D->getType();
   }

clang/test/AST/gh69468.cpp

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -verify %s
+
+
+a[i] = b[i]; // expected-error {{use of undeclared identifier 'i'}} \
+             // expected-error {{a type specifier is required for all declarations}} \
+	     // expected-error {{use of undeclared identifier 'b'}} \
+	     // expected-error {{use of undeclared identifier 'i'}}
+extern char b[];
+extern char a[];
+
+void foo(int j) {
+  // This used to crash here
+  a[j] = b[j];
+}