Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -375,6 +375,8 @@
   by making use of the syntactical structure of function calls. This avoids display
   of syntactically invalid codes in diagnostics.
   (`#57081: <https://github.com/llvm/llvm-project/issues/57081>`_)
+- Clang contexpr evaluator now displays notes as well as an error when a constructor
+  of base class is not called in the constructor of its derived class.
 
 Bug Fixes in This Version
 -------------------------
Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -70,10 +70,14 @@
   "is not a constant expression">;
 def note_constexpr_uninitialized : Note<
   "subobject %0 is not initialized">;
+def note_constexpr_uninitialized_base : Note<
+  "constructor of base class %0 is not called">;
 def note_constexpr_static_local : Note<
   "control flows through the definition of a %select{static|thread_local}0 variable">;
 def note_constexpr_subobject_declared_here : Note<
   "subobject declared here">;
+def note_constexpr_base_inherited_here : Note<
+  "base class inherited here">;
 def note_constexpr_array_index : Note<"cannot refer to element %0 of "
   "%select{array of %2 element%plural{1:|:s}2|non-array object}1 "
   "in a constant expression">;
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -2415,9 +2415,16 @@
     if (const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD)) {
       unsigned BaseIndex = 0;
       for (const CXXBaseSpecifier &BS : CD->bases()) {
-        if (!CheckEvaluationResult(CERK, Info, DiagLoc, BS.getType(),
-                                   Value.getStructBase(BaseIndex), Kind,
-                                   /*SubobjectDecl=*/nullptr, CheckedTemps))
+        const APValue &BaseValue = Value.getStructBase(BaseIndex);
+        if (!BaseValue.hasValue()) {
+          Info.FFDiag(DiagLoc, diag::note_constexpr_uninitialized_base)
+              << BS.getType();
+          Info.Note(BS.getBeginLoc(), diag::note_constexpr_base_inherited_here);
+          return false;
+        }
+        if (!CheckEvaluationResult(CERK, Info, DiagLoc, BS.getType(), BaseValue,
+                                   Kind, /*SubobjectDecl=*/nullptr,
+                                   CheckedTemps))
           return false;
         ++BaseIndex;
       }
Index: clang/test/SemaCXX/constexpr-subobj-initialization.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/constexpr-subobj-initialization.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+namespace baseclass_uninit {
+struct DelBase {
+  constexpr DelBase() = delete; // expected-note {{'DelBase' has been explicitly marked deleted here}}
+};
+
+struct Foo : DelBase {  // expected-note 2{{base class inherited here}}
+  constexpr Foo() {}; // expected-error {{call to deleted constructor of 'DelBase'}}
+};
+constexpr Foo f; // expected-error {{must be initialized by a constant expression}} \
+                 // expected-note {{constructor of base class 'DelBase' is not called}}
+struct Bar : Foo {
+  constexpr Bar() {};
+};
+constexpr Bar bar; // expected-error {{must be initialized by a constant expression}} \
+                   // expected-note {{constructor of base class 'DelBase' is not called}}
+
+struct Base {};
+struct A : Base { // expected-note {{base class inherited here}}
+  constexpr A() : value() {} // expected-error {{member initializer 'value' does not name a non-static data member or base class}}
+};
+
+constexpr A a; // expected-error {{must be initialized by a constant expression}} \
+               // expected-note {{constructor of base class 'Base' is not called}}
+
+struct B : Base { // expected-note {{base class inherited here}}
+  constexpr B() : {} // expected-error {{expected class member or base class name}}
+};
+
+constexpr B b; // expected-error {{must be initialized by a constant expression}} \
+               // expected-note {{constructor of base class 'Base' is not called}}
+} // namespace baseclass_uninit
+