diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -8643,9 +8643,13 @@
 
     case SK_ArrayLoopIndex: {
       Expr *Cur = CurInit.get();
-      Expr *BaseExpr = new (S.Context)
-          OpaqueValueExpr(Cur->getExprLoc(), Cur->getType(),
-                          Cur->getValueKind(), Cur->getObjectKind(), Cur);
+      // Prevent nested OpaqueValueExprs.
+      Expr *BaseExpr = dyn_cast<OpaqueValueExpr>(Cur);
+      if (!BaseExpr) {
+        BaseExpr = new (S.Context)
+            OpaqueValueExpr(Cur->getExprLoc(), Cur->getType(),
+                            Cur->getValueKind(), Cur->getObjectKind(), Cur);
+      }
       Expr *IndexExpr =
           new (S.Context) ArrayInitIndexExpr(S.Context.getSizeType());
       CurInit = S.CreateBuiltinArraySubscriptExpr(
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -10511,7 +10511,18 @@
 TreeTransform<Derived>::TransformOpaqueValueExpr(OpaqueValueExpr *E) {
   assert((!E->getSourceExpr() || getDerived().AlreadyTransformed(E->getType())) &&
          "opaque value expression requires transformation");
-  return E;
+
+  // Note that SourceExpr can be nullptr.
+  ExprResult SourceExpr = TransformExpr(E->getSourceExpr());
+  if (SourceExpr.isInvalid())
+    return ExprError();
+  if (SourceExpr.get() == E->getSourceExpr() && !getDerived().AlwaysRebuild())
+    return E;
+
+  OpaqueValueExpr *New = new (SemaRef.Context)
+      OpaqueValueExpr(E->getExprLoc(), E->getType(), E->getValueKind(),
+                      E->getObjectKind(), SourceExpr.get());
+  return New;
 }
 
 template<typename Derived>
diff --git a/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp b/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++1z -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+
+int a[1];
+// CHECK: @a = global [1 x i32] zeroinitializer
+template <int>
+void test_transform() {
+  auto [b] = a;
+}
+void (*d)(){test_transform<0>};
+// CHECK-LABEL: define {{.*}} @_Z14test_transformILi0EEvv
+// CHECK:       [[ENTRY:.*]]:
+// CHECK-NEXT:  [[ARR:%.*]] = alloca [1 x i32]
+// CHECK-NEXT:  [[BEGIN:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[ARR]], i64 0, i64 0
+// CHECK-NEXT:  br label %[[BODY:.*]]
+// CHECK-EMPTY:
+// CHECK-NEXT:  [[BODY]]:
+// CHECK-NEXT:  [[CUR:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[NEXT:%.*]], %[[BODY]] ]
+// CHECK-NEXT:  [[DEST:%.*]] = getelementptr inbounds i32, i32* [[BEGIN]], i64 [[CUR]]
+// CHECK-NEXT:  [[SRC:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* @a, i64 0, i64 [[CUR]]
+// CHECK-NEXT:  [[X:%.*]] = load i32, i32* [[SRC]]
+// CHECK-NEXT:  store i32 [[X]], i32* [[DEST]]
+// CHECK-NEXT:  [[NEXT]] = add nuw i64 [[CUR]], 1
+// CHECK-NEXT:  [[EQ:%.*]] = icmp eq i64 [[NEXT]], 1
+// CHECK-NEXT:  br i1 [[EQ]], label %[[FIN:.*]], label %[[BODY]]
+// CHECK-EMPTY:
+// CHECK-NEXT:  [[FIN]]:
+// CHECK-NEXT:  ret void