Index: clang/lib/Parse/ParseDeclCXX.cpp
===================================================================
--- clang/lib/Parse/ParseDeclCXX.cpp
+++ clang/lib/Parse/ParseDeclCXX.cpp
@@ -2974,11 +2974,20 @@
 /// be a constant-expression.
 ExprResult Parser::ParseCXXMemberInitializer(Decl *D, bool IsFunction,
                                              SourceLocation &EqualLoc) {
+  using EEC = Sema::ExpressionEvaluationContext;
+
   assert(Tok.isOneOf(tok::equal, tok::l_brace)
          && "Data member initializer not starting with '=' or '{'");
 
+  bool IsConstexpr = false;
+  if (auto *VD = dyn_cast_or_null<VarDecl>(D))
+    IsConstexpr = VD->isConstexpr();
+
   EnterExpressionEvaluationContext Context(
-      Actions, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, D);
+      Actions,
+      getLangOpts().CPlusPlus2a && IsConstexpr ? EEC::ConstantEvaluated
+                                               : EEC::PotentiallyEvaluated,
+      D);
   if (TryConsumeToken(tok::equal, EqualLoc)) {
     if (Tok.is(tok::kw_delete)) {
       // In principle, an initializer of '= delete p;' is legal, but it will
Index: clang/lib/Parse/ParseStmt.cpp
===================================================================
--- clang/lib/Parse/ParseStmt.cpp
+++ clang/lib/Parse/ParseStmt.cpp
@@ -1329,10 +1329,19 @@
   // Parse the condition.
   StmtResult InitStmt;
   Sema::ConditionResult Cond;
-  if (ParseParenExprOrCondition(&InitStmt, Cond, IfLoc,
-                                IsConstexpr ? Sema::ConditionKind::ConstexprIf
-                                            : Sema::ConditionKind::Boolean))
-    return StmtError();
+
+  {
+    EnterExpressionEvaluationContext Unevaluated(
+        Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated,
+        /*LambdaContextDecl=*/nullptr, /*ExprContext=*/
+        Sema::ExpressionEvaluationContextRecord::EK_Other,
+        /*ShouldEnter=*/IsConstexpr);
+
+    if (ParseParenExprOrCondition(&InitStmt, Cond, IfLoc,
+                                  IsConstexpr ? Sema::ConditionKind::ConstexprIf
+                                              : Sema::ConditionKind::Boolean))
+      return StmtError();
+  }
 
   llvm::Optional<bool> ConstexprCondition;
   if (IsConstexpr)
Index: clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -4644,7 +4644,9 @@
   Function->setInnerLocStart(PatternDecl->getInnerLocStart());
 
   EnterExpressionEvaluationContext EvalContext(
-      *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+      *this, PatternDecl->getConstexprKind() == CSK_consteval
+                 ? Sema::ExpressionEvaluationContext::ConstantEvaluated
+                 : Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   // Introduce a new scope where local variable instantiations will be
   // recorded, unless we're actually a member function within a local
@@ -4947,8 +4949,13 @@
     Var->setImplicitlyInline();
 
   if (OldVar->getInit()) {
+    bool IsConstexpr = OldVar->isConstexpr() || isConstantEvaluated();
     EnterExpressionEvaluationContext Evaluated(
-        *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, Var);
+        *this,
+        getLangOpts().CPlusPlus2a && IsConstexpr
+            ? Sema::ExpressionEvaluationContext::ConstantEvaluated
+            : Sema::ExpressionEvaluationContext::PotentiallyEvaluated,
+        Var);
 
     // Instantiate the initializer.
     ExprResult Init;
Index: clang/lib/Sema/TreeTransform.h
===================================================================
--- clang/lib/Sema/TreeTransform.h
+++ clang/lib/Sema/TreeTransform.h
@@ -12169,7 +12169,9 @@
   // FIXME: Sema's lambda-building mechanism expects us to push an expression
   // evaluation context even if we're not transforming the function body.
   getSema().PushExpressionEvaluationContext(
-      Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+      E->getCallOperator()->getConstexprKind() == CSK_consteval
+          ? Sema::ExpressionEvaluationContext::ConstantEvaluated
+          : Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   // Instantiate the body of the lambda expression.
   StmtResult Body =