Index: clang/lib/StaticAnalyzer/Core/RegionStore.cpp
===================================================================
--- clang/lib/StaticAnalyzer/Core/RegionStore.cpp
+++ clang/lib/StaticAnalyzer/Core/RegionStore.cpp
@@ -1660,7 +1660,7 @@
   } else if (const VarRegion *VR = dyn_cast<VarRegion>(superR)) {
     // Check if the containing array has an initialized value that we can trust.
     // We can trust a const value or a value of a global initializer in main().
-    const VarDecl *VD = VR->getDecl();
+    const VarDecl *VD = VR->getDecl()->getMostRecentDecl();
     if (VD->getType().isConstQualified() ||
         R->getElementType().isConstQualified() ||
         (B.isMainAnalysis() && VD->hasGlobalStorage())) {
@@ -1668,49 +1668,48 @@
         if (const auto *InitList = dyn_cast<InitListExpr>(Init)) {
           // The array index has to be known.
           if (auto CI = R->getIndex().getAs<nonloc::ConcreteInt>()) {
-            // If it is not an array, return Undef.
-            QualType T = VD->getType();
-            const ConstantArrayType *CAT = Ctx.getAsConstantArrayType(T);
-            if (!CAT)
-              return UndefinedVal();
-
-            // Support one-dimensional array.
-            // C++20 [expr.add] 7.6.6.4 (excerpt):
-            //   If P points to an array element i of an array object x with n
-            //   elements, where i < 0 or i > n, the behavior is undefined.
-            //   Dereferencing is not allowed on the "one past the last
-            //   element", when i == n.
-            // Example:
-            //   const int arr[4] = {1, 2};
-            //   const int *ptr = arr;
-            //   int x0 = ptr[0]; // 1
-            //   int x1 = ptr[1]; // 2
-            //   int x2 = ptr[2]; // 0
-            //   int x3 = ptr[3]; // 0
-            //   int x4 = ptr[4]; // UB
-            // TODO: Support multidimensional array.
-            if (!isa<ConstantArrayType>(CAT->getElementType())) {
-              // One-dimensional array.
-              const llvm::APSInt &Idx = CI->getValue();
-              const auto I = static_cast<uint64_t>(Idx.getExtValue());
-              // Use `getZExtValue` because array extent can not be negative.
-              const uint64_t Extent = CAT->getSize().getZExtValue();
-              // Check for `Idx < 0`, NOT for `I < 0`, because `Idx` CAN be
-              // negative, but `I` can NOT.
-              if (Idx < 0 || I >= Extent)
-                return UndefinedVal();
-
-              // C++20 [expr.add] 9.4.17.5 (excerpt):
-              //   i-th array element is value-initialized for each k < i ≤ n,
-              //   where k is an expression-list size and n is an array extent.
-              if (I >= InitList->getNumInits())
-                return svalBuilder.makeZeroVal(R->getElementType());
-
-              // Return a constant value, if it is presented.
-              // FIXME: Support other SVals.
-              const Expr *E = InitList->getInit(I);
-              if (Optional<SVal> V = svalBuilder.getConstantVal(E))
-                return *V;
+            // We treat only ConstantArrayType.
+            const QualType T = VD->getType();
+            if (const ConstantArrayType *CAT = Ctx.getAsConstantArrayType(T)) {
+              // Support one-dimensional array.
+              // C++20 [expr.add] 7.6.6.4 (excerpt):
+              //   If P points to an array element i of an array object x with n
+              //   elements, where i < 0 or i > n, the behavior is undefined.
+              //   Dereferencing is not allowed on the "one past the last
+              //   element", when i == n.
+              // Example:
+              //   const int arr[4] = {1, 2};
+              //   const int *ptr = arr;
+              //   int x0 = ptr[0]; // 1
+              //   int x1 = ptr[1]; // 2
+              //   int x2 = ptr[2]; // 0
+              //   int x3 = ptr[3]; // 0
+              //   int x4 = ptr[4]; // UB
+              // TODO: Support multidimensional array.
+              if (!isa<ConstantArrayType>(CAT->getElementType())) {
+                // One-dimensional array.
+                const llvm::APSInt &Idx = CI->getValue();
+                const auto I = static_cast<uint64_t>(Idx.getExtValue());
+                // Use `getZExtValue` because array extent can not be negative.
+                const uint64_t Extent = CAT->getSize().getZExtValue();
+                // Check for `Idx < 0`, NOT for `I < 0`, because `Idx` CAN be
+                // negative, but `I` can NOT.
+                if (Idx < 0 || I >= Extent)
+                  return UndefinedVal();
+
+                // C++20 [expr.add] 9.4.17.5 (excerpt):
+                //   i-th array element is value-initialized for each k < i ≤ n,
+                //   where k is an expression-list size and n is an array
+                //   extent.
+                if (I >= InitList->getNumInits())
+                  return svalBuilder.makeZeroVal(R->getElementType());
+
+                // Return a constant value, if it is presented.
+                // FIXME: Support other SVals.
+                const Expr *E = InitList->getInit(I);
+                if (Optional<SVal> V = svalBuilder.getConstantVal(E))
+                  return *V;
+              }
             }
           }
         }
Index: clang/test/Analysis/initialization.c
===================================================================
--- clang/test/Analysis/initialization.c
+++ clang/test/Analysis/initialization.c
@@ -97,3 +97,22 @@
   // FIXME: Should warn {{garbage or undefined}}.
   int res = glob_arr2[x][y]; // no-warning
 }
+
+const int glob_arr3[];              // Incomplete array declaration
+const int glob_arr3[4] = {1, 2, 3}; // Incomplete Array redeclaration
+void foo() {
+  clang_analyzer_eval(glob_arr3[0] == 1); // expected-warning{{TRUE}}
+  clang_analyzer_eval(glob_arr3[1] == 2); // expected-warning{{TRUE}}
+  clang_analyzer_eval(glob_arr3[2] == 3); // expected-warning{{TRUE}}
+  clang_analyzer_eval(glob_arr3[3] == 0); // expected-warning{{TRUE}}
+}
+
+void glob_invalid_index5() {
+  int x = 42;
+  int res = glob_arr3[x]; // expected-warning{{garbage or undefined}}
+}
+
+void glob_invalid_index6() {
+  int x = -42;
+  int res = glob_arr3[x]; // expected-warning{{garbage or undefined}}
+}