[clang] 26fa17e - Implement CWG2631

Corentin Jabot via cfe-commits cfe-commits at lists.llvm.org
Wed Nov 30 02:25:09 PST 2022


Author: Corentin Jabot
Date: 2022-11-30T11:25:01+01:00
New Revision: 26fa17ed2914bd80c066d36b325fd3104e45554c

URL: https://github.com/llvm/llvm-project/commit/26fa17ed2914bd80c066d36b325fd3104e45554c
DIFF: https://github.com/llvm/llvm-project/commit/26fa17ed2914bd80c066d36b325fd3104e45554c.diff

LOG: Implement CWG2631

Implement https://cplusplus.github.io/CWG/issues/2631.html.

Immediate calls in default arguments and defaults members
are not evaluated.

Instead, we evaluate them when constructing a
`CXXDefaultArgExpr`/`BuildCXXDefaultInitExpr`.

The immediate calls are executed by doing a
transform on the initializing expression.

Note that lambdas are not considering subexpressions so
we do not need to transform them.

As a result of this patch, unused default member
initializers are not considered odr-used, and
errors about members binding to local variables
in an outer scope only surface at the point
where a constructor is defined.

Reviewed By: aaron.ballman, #clang-language-wg

Differential Revision: https://reviews.llvm.org/D136554

Added: 
    clang/test/CodeGenCXX/default-arguments-with-immediate.cpp
    clang/test/PCH/default-argument-with-immediate-calls.cpp
    clang/test/SemaCXX/cxx2a-consteval-default-params.cpp

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/include/clang/AST/ExprCXX.h
    clang/include/clang/AST/Stmt.h
    clang/include/clang/Basic/DiagnosticSemaKinds.td
    clang/include/clang/Sema/Sema.h
    clang/lib/AST/ASTImporter.cpp
    clang/lib/AST/Decl.cpp
    clang/lib/AST/ExprCXX.cpp
    clang/lib/Parse/ParseCXXInlineMethods.cpp
    clang/lib/Parse/ParseDeclCXX.cpp
    clang/lib/Sema/SemaDeclCXX.cpp
    clang/lib/Sema/SemaExpr.cpp
    clang/lib/Sema/SemaTemplateInstantiate.cpp
    clang/lib/Sema/TreeTransform.h
    clang/lib/Serialization/ASTReaderStmt.cpp
    clang/lib/Serialization/ASTWriterStmt.cpp
    clang/test/CXX/class/class.local/p1-0x.cpp
    clang/test/CXX/drs/dr26xx.cpp
    clang/test/CodeGenCXX/builtin-source-location.cpp
    clang/test/SemaCXX/cxx11-default-member-initializers.cpp
    clang/test/SemaCXX/source_location.cpp
    clang/www/cxx_dr_status.html

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7580b14fac5d6..c0dfc3ccb5a5a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -616,8 +616,16 @@ C++ Language Changes in Clang
   conforming GNU extensions. Projects incompatible with C++17 can add
   ``-std=gnu++14`` to their build settings to restore the previous behaviour.
 - Implemented DR2358 allowing init captures in lambdas in default arguments.
+<<<<<<< HEAD
 - implemented `DR2654 <https://wg21.link/cwg2654>`_ which undeprecates
   all compound assignements operations on volatile qualified variables.
+=======
+- Implemented DR2631. Invalid ``consteval`` calls in default arguments and default
+  member initializers are diagnosed when and if the default is used.
+  This Fixes `Issue 56379 <https://github.com/llvm/llvm-project/issues/56379>`_
+  and changes the value of ``std::source_location::current()``
+  used in default parameters calls compared to previous versions of Clang.
+>>>>>>> 7c4d4089e1fd (Implement CWG2631)
 
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^

diff  --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index 0b927c0294752..098720d9469f0 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -1245,8 +1245,12 @@ class CXXThrowExpr : public Expr {
 /// This wraps up a function call argument that was created from the
 /// corresponding parameter's default argument, when the call did not
 /// explicitly supply arguments for all of the parameters.
-class CXXDefaultArgExpr final : public Expr {
+class CXXDefaultArgExpr final
+    : public Expr,
+      private llvm::TrailingObjects<CXXDefaultArgExpr, Expr *> {
   friend class ASTStmtReader;
+  friend class ASTReader;
+  friend TrailingObjects;
 
   /// The parameter whose default is being used.
   ParmVarDecl *Param;
@@ -1255,7 +1259,7 @@ class CXXDefaultArgExpr final : public Expr {
   DeclContext *UsedContext;
 
   CXXDefaultArgExpr(StmtClass SC, SourceLocation Loc, ParmVarDecl *Param,
-                    DeclContext *UsedContext)
+                    Expr *RewrittenExpr, DeclContext *UsedContext)
       : Expr(SC,
              Param->hasUnparsedDefaultArg()
                  ? Param->getType().getNonReferenceType()
@@ -1264,28 +1268,58 @@ class CXXDefaultArgExpr final : public Expr {
              Param->getDefaultArg()->getObjectKind()),
         Param(Param), UsedContext(UsedContext) {
     CXXDefaultArgExprBits.Loc = Loc;
+    CXXDefaultArgExprBits.HasRewrittenInit = RewrittenExpr != nullptr;
+    if (RewrittenExpr)
+      *getTrailingObjects<Expr *>() = RewrittenExpr;
     setDependence(computeDependence(this));
   }
 
+  CXXDefaultArgExpr(EmptyShell Empty, bool HasRewrittenInit)
+      : Expr(CXXDefaultArgExprClass, Empty) {
+    CXXDefaultArgExprBits.HasRewrittenInit = HasRewrittenInit;
+  }
+
+  size_t numTrailingObjects() const {
+    return CXXDefaultArgExprBits.HasRewrittenInit;
+  }
+
 public:
-  CXXDefaultArgExpr(EmptyShell Empty) : Expr(CXXDefaultArgExprClass, Empty) {}
+  static CXXDefaultArgExpr *CreateEmpty(const ASTContext &C,
+                                        bool HasRewrittenInit);
 
   // \p Param is the parameter whose default argument is used by this
   // expression.
   static CXXDefaultArgExpr *Create(const ASTContext &C, SourceLocation Loc,
-                                   ParmVarDecl *Param,
-                                   DeclContext *UsedContext) {
-    return new (C)
-        CXXDefaultArgExpr(CXXDefaultArgExprClass, Loc, Param, UsedContext);
-  }
-
+                                   ParmVarDecl *Param, Expr *RewrittenExpr,
+                                   DeclContext *UsedContext);
   // Retrieve the parameter that the argument was created from.
   const ParmVarDecl *getParam() const { return Param; }
   ParmVarDecl *getParam() { return Param; }
 
-  // Retrieve the actual argument to the function call.
-  const Expr *getExpr() const { return getParam()->getDefaultArg(); }
-  Expr *getExpr() { return getParam()->getDefaultArg(); }
+  bool hasRewrittenInit() const {
+    return CXXDefaultArgExprBits.HasRewrittenInit;
+  }
+
+  // Retrieve the argument to the function call.
+  Expr *getExpr();
+  const Expr *getExpr() const {
+    return const_cast<CXXDefaultArgExpr *>(this)->getExpr();
+  }
+
+  Expr *getRewrittenExpr() {
+    return hasRewrittenInit() ? *getTrailingObjects<Expr *>() : nullptr;
+  }
+
+  const Expr *getRewrittenExpr() const {
+    return const_cast<CXXDefaultArgExpr *>(this)->getRewrittenExpr();
+  }
+
+  // Retrieve the rewritten init expression (for an init expression containing
+  // immediate calls) with the top level FullExpr and ConstantExpr stripped off.
+  Expr *getAdjustedRewrittenExpr();
+  const Expr *getAdjustedRewrittenExpr() const {
+    return const_cast<CXXDefaultArgExpr *>(this)->getAdjustedRewrittenExpr();
+  }
 
   const DeclContext *getUsedContext() const { return UsedContext; }
   DeclContext *getUsedContext() { return UsedContext; }
@@ -1322,10 +1356,13 @@ class CXXDefaultArgExpr final : public Expr {
 /// is implicitly used in a mem-initializer-list in a constructor
 /// (C++11 [class.base.init]p8) or in aggregate initialization
 /// (C++1y [dcl.init.aggr]p7).
-class CXXDefaultInitExpr : public Expr {
-  friend class ASTReader;
-  friend class ASTStmtReader;
+class CXXDefaultInitExpr final
+    : public Expr,
+      private llvm::TrailingObjects<CXXDefaultArgExpr, Expr *> {
 
+  friend class ASTStmtReader;
+  friend class ASTReader;
+  friend TrailingObjects;
   /// The field whose default is being used.
   FieldDecl *Field;
 
@@ -1333,16 +1370,29 @@ class CXXDefaultInitExpr : public Expr {
   DeclContext *UsedContext;
 
   CXXDefaultInitExpr(const ASTContext &Ctx, SourceLocation Loc,
-                     FieldDecl *Field, QualType Ty, DeclContext *UsedContext);
+                     FieldDecl *Field, QualType Ty, DeclContext *UsedContext,
+                     Expr *RewrittenInitExpr);
+
+  CXXDefaultInitExpr(EmptyShell Empty, bool HasRewrittenInit)
+      : Expr(CXXDefaultInitExprClass, Empty) {
+    CXXDefaultInitExprBits.HasRewrittenInit = HasRewrittenInit;
+  }
 
-  CXXDefaultInitExpr(EmptyShell Empty) : Expr(CXXDefaultInitExprClass, Empty) {}
+  size_t numTrailingObjects() const {
+    return CXXDefaultInitExprBits.HasRewrittenInit;
+  }
 
 public:
+  static CXXDefaultInitExpr *CreateEmpty(const ASTContext &C,
+                                         bool HasRewrittenInit);
   /// \p Field is the non-static data member whose default initializer is used
   /// by this expression.
   static CXXDefaultInitExpr *Create(const ASTContext &Ctx, SourceLocation Loc,
-                                    FieldDecl *Field, DeclContext *UsedContext) {
-    return new (Ctx) CXXDefaultInitExpr(Ctx, Loc, Field, Field->getType(), UsedContext);
+                                    FieldDecl *Field, DeclContext *UsedContext,
+                                    Expr *RewrittenInitExpr);
+
+  bool hasRewrittenInit() const {
+    return CXXDefaultInitExprBits.HasRewrittenInit;
   }
 
   /// Get the field whose initializer will be used.
@@ -1350,13 +1400,23 @@ class CXXDefaultInitExpr : public Expr {
   const FieldDecl *getField() const { return Field; }
 
   /// Get the initialization expression that will be used.
+  Expr *getExpr();
   const Expr *getExpr() const {
-    assert(Field->getInClassInitializer() && "initializer hasn't been parsed");
-    return Field->getInClassInitializer();
+    return const_cast<CXXDefaultInitExpr *>(this)->getExpr();
+  }
+
+  /// Retrieve the initializing expression with evaluated immediate calls, if
+  /// any.
+  const Expr *getRewrittenExpr() const {
+    assert(hasRewrittenInit() && "expected a rewritten init expression");
+    return *getTrailingObjects<Expr *>();
   }
-  Expr *getExpr() {
-    assert(Field->getInClassInitializer() && "initializer hasn't been parsed");
-    return Field->getInClassInitializer();
+
+  /// Retrieve the initializing expression with evaluated immediate calls, if
+  /// any.
+  Expr *getRewrittenExpr() {
+    assert(hasRewrittenInit() && "expected a rewritten init expression");
+    return *getTrailingObjects<Expr *>();
   }
 
   const DeclContext *getUsedContext() const { return UsedContext; }

diff  --git a/clang/include/clang/AST/Stmt.h b/clang/include/clang/AST/Stmt.h
index c65cdeb574cc9..7f9d36ec1c4be 100644
--- a/clang/include/clang/AST/Stmt.h
+++ b/clang/include/clang/AST/Stmt.h
@@ -690,6 +690,9 @@ class alignas(void *) Stmt {
 
     unsigned : NumExprBits;
 
+    /// Whether this CXXDefaultArgExpr rewrote its argument and stores a copy.
+    unsigned HasRewrittenInit : 1;
+
     /// The location where the default argument expression was used.
     SourceLocation Loc;
   };
@@ -700,6 +703,10 @@ class alignas(void *) Stmt {
 
     unsigned : NumExprBits;
 
+    /// Whether this CXXDefaultInitExprBitfields rewrote its argument and stores
+    /// a copy.
+    unsigned HasRewrittenInit : 1;
+
     /// The location where the default initializer expression was used.
     SourceLocation Loc;
   };

diff  --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 15f85b778ccc6..e13f059933a97 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2646,6 +2646,10 @@ def err_invalid_consteval_take_address : Error<
   " of an immediate invocation">;
 def err_invalid_consteval_call : Error<
   "call to consteval function %q0 is not a constant expression">;
+def note_invalid_consteval_initializer : Note<
+  "in the default initalizer of %0">;
+def note_invalid_consteval_initializer_here : Note<
+  "initialized here %0">;
 def err_invalid_consteval_decl_kind : Error<
   "%0 cannot be declared consteval">;
 def err_invalid_constexpr : Error<

diff  --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index e4ae554114807..a8614f742a7e9 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1330,6 +1330,25 @@ class Sema final {
     bool InDiscardedStatement;
     bool InImmediateFunctionContext;
 
+    bool IsCurrentlyCheckingDefaultArgumentOrInitializer = false;
+
+    // When evaluating immediate functions in the initializer of a default
+    // argument or default member initializer, this is the declaration whose
+    // default initializer is being evaluated and the location of the call
+    // or constructor definition.
+    struct InitializationContext {
+      InitializationContext(SourceLocation Loc, ValueDecl *Decl,
+                            DeclContext *Context)
+          : Loc(Loc), Decl(Decl), Context(Context) {
+        assert(Decl && Context && "invalid initialization context");
+      }
+
+      SourceLocation Loc;
+      ValueDecl *Decl = nullptr;
+      DeclContext *Context = nullptr;
+    };
+    llvm::Optional<InitializationContext> DelayedDefaultInitializationContext;
+
     ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                       unsigned NumCleanupObjects,
                                       CleanupInfo ParentCleanup,
@@ -6210,19 +6229,22 @@ class Sema final {
                         bool IsStdInitListInitialization, bool RequiresZeroInit,
                         unsigned ConstructKind, SourceRange ParenRange);
 
+  ExprResult ConvertMemberDefaultInitExpression(FieldDecl *FD, Expr *InitExpr,
+                                                SourceLocation InitLoc);
+
   ExprResult BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field);
 
 
   /// Instantiate or parse a C++ default argument expression as necessary.
   /// Return true on error.
   bool CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
-                              ParmVarDecl *Param);
+                              ParmVarDecl *Param, Expr *Init = nullptr,
+                              bool SkipImmediateInvocations = true);
 
   /// BuildCXXDefaultArgExpr - Creates a CXXDefaultArgExpr, instantiating
   /// the default expr if needed.
-  ExprResult BuildCXXDefaultArgExpr(SourceLocation CallLoc,
-                                    FunctionDecl *FD,
-                                    ParmVarDecl *Param);
+  ExprResult BuildCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
+                                    ParmVarDecl *Param, Expr *Init = nullptr);
 
   /// FinalizeVarWithDestructor - Prepare for calling destructor on the
   /// constructed variable.
@@ -9626,6 +9648,63 @@ class Sema final {
     return ExprEvalContexts.back().isImmediateFunctionContext();
   }
 
+  bool isCheckingDefaultArgumentOrInitializer() const {
+    assert(!ExprEvalContexts.empty() &&
+           "Must be in an expression evaluation context");
+    const ExpressionEvaluationContextRecord &Ctx = ExprEvalContexts.back();
+    return (Ctx.Context ==
+            ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed) ||
+           Ctx.IsCurrentlyCheckingDefaultArgumentOrInitializer;
+  }
+
+  bool isCheckingDefaultArgumentOrInitializerOfOuterEntity() const {
+    assert(!ExprEvalContexts.empty() &&
+           "Must be in an expression evaluation context");
+    for (const auto &Ctx : llvm::reverse(ExprEvalContexts)) {
+      if ((Ctx.Context ==
+           ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed) ||
+          Ctx.IsCurrentlyCheckingDefaultArgumentOrInitializer)
+        return true;
+      if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
+          Ctx.isUnevaluated())
+        return false;
+    }
+    return false;
+  }
+
+  llvm::Optional<ExpressionEvaluationContextRecord::InitializationContext>
+  InnermostDeclarationWithDelayedImmediateInvocations() const {
+    assert(!ExprEvalContexts.empty() &&
+           "Must be in an expression evaluation context");
+    for (const auto &Ctx : llvm::reverse(ExprEvalContexts)) {
+      if (Ctx.Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
+          Ctx.DelayedDefaultInitializationContext)
+        return Ctx.DelayedDefaultInitializationContext;
+      if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
+          Ctx.isUnevaluated())
+        break;
+    }
+    return llvm::None;
+  }
+
+  llvm::Optional<ExpressionEvaluationContextRecord::InitializationContext>
+  OutermostDeclarationWithDelayedImmediateInvocations() const {
+    assert(!ExprEvalContexts.empty() &&
+           "Must be in an expression evaluation context");
+    llvm::Optional<ExpressionEvaluationContextRecord::InitializationContext>
+        Res;
+    for (auto &Ctx : llvm::reverse(ExprEvalContexts)) {
+      if (Ctx.Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
+          !Ctx.DelayedDefaultInitializationContext && Res)
+        break;
+      if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
+          Ctx.isUnevaluated())
+        break;
+      Res = Ctx.DelayedDefaultInitializationContext;
+    }
+    return Res;
+  }
+
   /// RAII class used to determine whether SFINAE has
   /// trapped any errors that occur during template argument
   /// deduction.

diff  --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 2c728911ee06b..42e903724663f 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -7687,9 +7687,16 @@ ExpectedStmt ASTNodeImporter::VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
     if (Error Err = ImportDefaultArgOfParmVarDecl(*FromParam, ToParam))
       return std::move(Err);
   }
-
+  Expr *RewrittenInit = nullptr;
+  if (E->hasRewrittenInit()) {
+    ExpectedExpr ExprOrErr = import(E->getExpr());
+    if (!ExprOrErr)
+      return ExprOrErr.takeError();
+    RewrittenInit = ExprOrErr.get();
+  }
   return CXXDefaultArgExpr::Create(Importer.getToContext(), *ToUsedLocOrErr,
-                                   *ToParamOrErr, *UsedContextOrErr);
+                                   *ToParamOrErr, RewrittenInit,
+                                   *UsedContextOrErr);
 }
 
 ExpectedStmt
@@ -8381,8 +8388,16 @@ ExpectedStmt ASTNodeImporter::VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
     ToField->setInClassInitializer(*ToInClassInitializerOrErr);
   }
 
+  Expr *RewrittenInit = nullptr;
+  if (E->hasRewrittenInit()) {
+    ExpectedExpr ExprOrErr = import(E->getExpr());
+    if (!ExprOrErr)
+      return ExprOrErr.takeError();
+    RewrittenInit = ExprOrErr.get();
+  }
+
   return CXXDefaultInitExpr::Create(Importer.getToContext(), *ToBeginLocOrErr,
-                                    ToField, *UsedContextOrErr);
+                                    ToField, *UsedContextOrErr, RewrittenInit);
 }
 
 ExpectedStmt ASTNodeImporter::VisitCXXNamedCastExpr(CXXNamedCastExpr *E) {

diff  --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 1efe9c6d40dc0..8d9b97fafb230 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2888,8 +2888,7 @@ Expr *ParmVarDecl::getDefaultArg() {
 
   Expr *Arg = getInit();
   if (auto *E = dyn_cast_or_null<FullExpr>(Arg))
-    if (!isa<ConstantExpr>(E))
-      return E->getSubExpr();
+    return E->getSubExpr();
 
   return Arg;
 }

diff  --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index 3bf3eab72846c..6a6f692dec787 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -949,9 +949,43 @@ const IdentifierInfo *UserDefinedLiteral::getUDSuffix() const {
   return cast<FunctionDecl>(getCalleeDecl())->getLiteralIdentifier();
 }
 
+CXXDefaultArgExpr *CXXDefaultArgExpr::CreateEmpty(const ASTContext &C,
+                                                  bool HasRewrittenInit) {
+  size_t Size = totalSizeToAlloc<Expr *>(HasRewrittenInit);
+  auto *Mem = C.Allocate(Size, alignof(CXXDefaultArgExpr));
+  return new (Mem) CXXDefaultArgExpr(EmptyShell(), HasRewrittenInit);
+}
+
+CXXDefaultArgExpr *CXXDefaultArgExpr::Create(const ASTContext &C,
+                                             SourceLocation Loc,
+                                             ParmVarDecl *Param,
+                                             Expr *RewrittenExpr,
+                                             DeclContext *UsedContext) {
+  size_t Size = totalSizeToAlloc<Expr *>(RewrittenExpr != nullptr);
+  auto *Mem = C.Allocate(Size, alignof(CXXDefaultArgExpr));
+  return new (Mem) CXXDefaultArgExpr(CXXDefaultArgExprClass, Loc, Param,
+                                     RewrittenExpr, UsedContext);
+}
+
+Expr *CXXDefaultArgExpr::getExpr() {
+  return CXXDefaultArgExprBits.HasRewrittenInit ? getAdjustedRewrittenExpr()
+                                                : getParam()->getDefaultArg();
+}
+
+Expr *CXXDefaultArgExpr::getAdjustedRewrittenExpr() {
+  assert(hasRewrittenInit() &&
+         "expected this CXXDefaultArgExpr to have a rewritten init.");
+  Expr *Init = getRewrittenExpr();
+  if (auto *E = dyn_cast_if_present<FullExpr>(Init))
+    if (!isa<ConstantExpr>(E))
+      return E->getSubExpr();
+  return Init;
+}
+
 CXXDefaultInitExpr::CXXDefaultInitExpr(const ASTContext &Ctx,
                                        SourceLocation Loc, FieldDecl *Field,
-                                       QualType Ty, DeclContext *UsedContext)
+                                       QualType Ty, DeclContext *UsedContext,
+                                       Expr *RewrittenInitExpr)
     : Expr(CXXDefaultInitExprClass, Ty.getNonLValueExprType(Ctx),
            Ty->isLValueReferenceType()   ? VK_LValue
            : Ty->isRValueReferenceType() ? VK_XValue
@@ -959,11 +993,43 @@ CXXDefaultInitExpr::CXXDefaultInitExpr(const ASTContext &Ctx,
            /*FIXME*/ OK_Ordinary),
       Field(Field), UsedContext(UsedContext) {
   CXXDefaultInitExprBits.Loc = Loc;
+  CXXDefaultInitExprBits.HasRewrittenInit = RewrittenInitExpr != nullptr;
+
+  if (CXXDefaultInitExprBits.HasRewrittenInit)
+    *getTrailingObjects<Expr *>() = RewrittenInitExpr;
+
   assert(Field->hasInClassInitializer());
 
   setDependence(computeDependence(this));
 }
 
+CXXDefaultInitExpr *CXXDefaultInitExpr::CreateEmpty(const ASTContext &C,
+                                                    bool HasRewrittenInit) {
+  size_t Size = totalSizeToAlloc<Expr *>(HasRewrittenInit);
+  auto *Mem = C.Allocate(Size, alignof(CXXDefaultInitExpr));
+  return new (Mem) CXXDefaultInitExpr(EmptyShell(), HasRewrittenInit);
+}
+
+CXXDefaultInitExpr *CXXDefaultInitExpr::Create(const ASTContext &Ctx,
+                                               SourceLocation Loc,
+                                               FieldDecl *Field,
+                                               DeclContext *UsedContext,
+                                               Expr *RewrittenInitExpr) {
+
+  size_t Size = totalSizeToAlloc<Expr *>(RewrittenInitExpr != nullptr);
+  auto *Mem = Ctx.Allocate(Size, alignof(CXXDefaultArgExpr));
+  return new (Mem) CXXDefaultInitExpr(Ctx, Loc, Field, Field->getType(),
+                                      UsedContext, RewrittenInitExpr);
+}
+
+Expr *CXXDefaultInitExpr::getExpr() {
+  assert(Field->getInClassInitializer() && "initializer hasn't been parsed");
+  if (hasRewrittenInit())
+    return getRewrittenExpr();
+
+  return Field->getInClassInitializer();
+}
+
 CXXTemporary *CXXTemporary::Create(const ASTContext &C,
                                    const CXXDestructorDecl *Destructor) {
   return new (C) CXXTemporary(Destructor);

diff  --git a/clang/lib/Parse/ParseCXXInlineMethods.cpp b/clang/lib/Parse/ParseCXXInlineMethods.cpp
index d918ea26b9d9d..3a7f5426d4a70 100644
--- a/clang/lib/Parse/ParseCXXInlineMethods.cpp
+++ b/clang/lib/Parse/ParseCXXInlineMethods.cpp
@@ -648,6 +648,11 @@ void Parser::ParseLexedMemberInitializer(LateParsedMemberInitializer &MI) {
 
   Actions.ActOnStartCXXInClassMemberInitializer();
 
+  // The initializer isn't actually potentially evaluated unless it is
+  // used.
+  EnterExpressionEvaluationContext Eval(
+      Actions, Sema::ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed);
+
   ExprResult Init = ParseCXXMemberInitializer(MI.Field, /*IsFunction=*/false,
                                               EqualLoc);
 

diff  --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index e244cfc9948ce..2402ad5416785 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -3188,7 +3188,11 @@ ExprResult Parser::ParseCXXMemberInitializer(Decl *D, bool IsFunction,
          "Data member initializer not starting with '=' or '{'");
 
   EnterExpressionEvaluationContext Context(
-      Actions, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, D);
+      Actions,
+      isa_and_present<FieldDecl>(D)
+          ? Sema::ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed
+          : Sema::ExpressionEvaluationContext::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

diff  --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 194298ab5f7bf..fe33f6f360771 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -4059,6 +4059,21 @@ ExprResult Sema::ActOnRequiresClause(ExprResult ConstraintExpr) {
   return ConstraintExpr;
 }
 
+ExprResult Sema::ConvertMemberDefaultInitExpression(FieldDecl *FD,
+                                                    Expr *InitExpr,
+                                                    SourceLocation InitLoc) {
+  InitializedEntity Entity =
+      InitializedEntity::InitializeMemberFromDefaultMemberInitializer(FD);
+  InitializationKind Kind =
+      FD->getInClassInitStyle() == ICIS_ListInit
+          ? InitializationKind::CreateDirectList(InitExpr->getBeginLoc(),
+                                                 InitExpr->getBeginLoc(),
+                                                 InitExpr->getEndLoc())
+          : InitializationKind::CreateCopy(InitExpr->getBeginLoc(), InitLoc);
+  InitializationSequence Seq(*this, Entity, Kind, InitExpr);
+  return Seq.Perform(*this, Entity, Kind, InitExpr);
+}
+
 /// This is invoked after parsing an in-class initializer for a
 /// non-static C++ class member, and after instantiating an in-class initializer
 /// in a class template. Such actions are deferred until the class is complete.
@@ -4087,31 +4102,13 @@ void Sema::ActOnFinishCXXInClassMemberInitializer(Decl *D,
 
   ExprResult Init = InitExpr;
   if (!FD->getType()->isDependentType() && !InitExpr->isTypeDependent()) {
-    InitializedEntity Entity =
-        InitializedEntity::InitializeMemberFromDefaultMemberInitializer(FD);
-    InitializationKind Kind =
-        FD->getInClassInitStyle() == ICIS_ListInit
-            ? InitializationKind::CreateDirectList(InitExpr->getBeginLoc(),
-                                                   InitExpr->getBeginLoc(),
-                                                   InitExpr->getEndLoc())
-            : InitializationKind::CreateCopy(InitExpr->getBeginLoc(), InitLoc);
-    InitializationSequence Seq(*this, Entity, Kind, InitExpr);
-    Init = Seq.Perform(*this, Entity, Kind, InitExpr);
+    Init = ConvertMemberDefaultInitExpression(FD, InitExpr, InitLoc);
     if (Init.isInvalid()) {
       FD->setInvalidDecl();
       return;
     }
   }
 
-  // C++11 [class.base.init]p7:
-  //   The initialization of each base and member constitutes a
-  //   full-expression.
-  Init = ActOnFinishFullExpr(Init.get(), InitLoc, /*DiscardedValue*/ false);
-  if (Init.isInvalid()) {
-    FD->setInvalidDecl();
-    return;
-  }
-
   InitExpr = Init.get();
 
   FD->setInClassInitializer(InitExpr);
@@ -15647,70 +15644,6 @@ Sema::BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
       Constructor);
 }
 
-ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
-  assert(Field->hasInClassInitializer());
-
-  // If we already have the in-class initializer nothing needs to be done.
-  if (Field->getInClassInitializer())
-    return CXXDefaultInitExpr::Create(Context, Loc, Field, CurContext);
-
-  // If we might have already tried and failed to instantiate, don't try again.
-  if (Field->isInvalidDecl())
-    return ExprError();
-
-  // Maybe we haven't instantiated the in-class initializer. Go check the
-  // pattern FieldDecl to see if it has one.
-  CXXRecordDecl *ParentRD = cast<CXXRecordDecl>(Field->getParent());
-
-  if (isTemplateInstantiation(ParentRD->getTemplateSpecializationKind())) {
-    CXXRecordDecl *ClassPattern = ParentRD->getTemplateInstantiationPattern();
-    DeclContext::lookup_result Lookup =
-        ClassPattern->lookup(Field->getDeclName());
-
-    FieldDecl *Pattern = nullptr;
-    for (auto *L : Lookup) {
-      if (isa<FieldDecl>(L)) {
-        Pattern = cast<FieldDecl>(L);
-        break;
-      }
-    }
-    assert(Pattern && "We must have set the Pattern!");
-
-    if (!Pattern->hasInClassInitializer() ||
-        InstantiateInClassInitializer(Loc, Field, Pattern,
-                                      getTemplateInstantiationArgs(Field))) {
-      // Don't diagnose this again.
-      Field->setInvalidDecl();
-      return ExprError();
-    }
-    return CXXDefaultInitExpr::Create(Context, Loc, Field, CurContext);
-  }
-
-  // DR1351:
-  //   If the brace-or-equal-initializer of a non-static data member
-  //   invokes a defaulted default constructor of its class or of an
-  //   enclosing class in a potentially evaluated subexpression, the
-  //   program is ill-formed.
-  //
-  // This resolution is unworkable: the exception specification of the
-  // default constructor can be needed in an unevaluated context, in
-  // particular, in the operand of a noexcept-expression, and we can be
-  // unable to compute an exception specification for an enclosed class.
-  //
-  // Any attempt to resolve the exception specification of a defaulted default
-  // constructor before the initializer is lexically complete will ultimately
-  // come here at which point we can diagnose it.
-  RecordDecl *OutermostClass = ParentRD->getOuterLexicalRecordContext();
-  Diag(Loc, diag::err_default_member_initializer_not_yet_parsed)
-      << OutermostClass << Field;
-  Diag(Field->getEndLoc(),
-       diag::note_default_member_initializer_not_yet_parsed);
-  // Recover by marking the field invalid, unless we're in a SFINAE context.
-  if (!isSFINAEContext())
-    Field->setInvalidDecl();
-  return ExprError();
-}
-
 void Sema::FinalizeVarWithDestructor(VarDecl *VD, const RecordType *Record) {
   if (VD->isInvalidDecl()) return;
   // If initializing the variable failed, don't also diagnose problems with

diff  --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 06c70fbba6ffa..9d9107f78d74b 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -5856,8 +5856,10 @@ Sema::CreateBuiltinArraySubscriptExpr(Expr *Base, SourceLocation LLoc,
 }
 
 bool Sema::CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
-                                  ParmVarDecl *Param) {
+                                  ParmVarDecl *Param, Expr *RewrittenInit,
+                                  bool SkipImmediateInvocations) {
   if (Param->hasUnparsedDefaultArg()) {
+    assert(!RewrittenInit && "Should not have a rewritten init expression yet");
     // If we've already cleared out the location for the default argument,
     // that means we're parsing it right now.
     if (!UnparsedDefaultArgLocs.count(Param)) {
@@ -5874,11 +5876,14 @@ bool Sema::CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
     return true;
   }
 
-  if (Param->hasUninstantiatedDefaultArg() &&
-      InstantiateDefaultArgument(CallLoc, FD, Param))
-    return true;
+  if (Param->hasUninstantiatedDefaultArg()) {
+    assert(!RewrittenInit && "Should not have a rewitten init expression yet");
+    if (InstantiateDefaultArgument(CallLoc, FD, Param))
+      return true;
+  }
 
-  assert(Param->hasInit() && "default argument but no initializer?");
+  Expr *Init = RewrittenInit ? RewrittenInit : Param->getInit();
+  assert(Init && "default argument but no initializer?");
 
   // If the default expression creates temporaries, we need to
   // push them to the current stack of expression temporaries so they'll
@@ -5887,34 +5892,250 @@ bool Sema::CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
   // bound temporaries; see the comment in PR5810.
   // We don't need to do that with block decls, though, because
   // blocks in default argument expression can never capture anything.
-  if (auto Init = dyn_cast<ExprWithCleanups>(Param->getInit())) {
+  if (auto *InitWithCleanup = dyn_cast<ExprWithCleanups>(Init)) {
     // Set the "needs cleanups" bit regardless of whether there are
     // any explicit objects.
-    Cleanup.setExprNeedsCleanups(Init->cleanupsHaveSideEffects());
-
+    Cleanup.setExprNeedsCleanups(InitWithCleanup->cleanupsHaveSideEffects());
     // Append all the objects to the cleanup list.  Right now, this
     // should always be a no-op, because blocks in default argument
     // expressions should never be able to capture anything.
-    assert(!Init->getNumObjects() &&
+    assert(!InitWithCleanup->getNumObjects() &&
            "default argument expression has capturing blocks?");
   }
-
-  // We already type-checked the argument, so we know it works.
-  // Just mark all of the declarations in this potentially-evaluated expression
-  // as being "referenced".
   EnterExpressionEvaluationContext EvalContext(
       *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
-  MarkDeclarationsReferencedInExpr(Param->getDefaultArg(),
-                                   /*SkipLocalVariables=*/true);
+  ExprEvalContexts.back().IsCurrentlyCheckingDefaultArgumentOrInitializer =
+      SkipImmediateInvocations;
+  MarkDeclarationsReferencedInExpr(Init, /*SkipLocalVariables*/ true);
   return false;
 }
 
+struct ImmediateCallVisitor : public RecursiveASTVisitor<ImmediateCallVisitor> {
+  bool HasImmediateCalls = false;
+
+  bool VisitCallExpr(CallExpr *E) {
+    if (const FunctionDecl *FD = E->getDirectCallee())
+      HasImmediateCalls |= FD->isConsteval();
+    return RecursiveASTVisitor<ImmediateCallVisitor>::VisitStmt(E);
+  }
+
+  // SourceLocExpr are not immediate invocations
+  // but CXXDefaultInitExpr/CXXDefaultArgExpr containing a SourceLocExpr
+  // need to be rebuilt so that they refer to the correct SourceLocation and
+  // DeclContext.
+  bool VisitSourceLocExpr(SourceLocExpr *E) {
+    HasImmediateCalls = true;
+    return RecursiveASTVisitor<ImmediateCallVisitor>::VisitStmt(E);
+  }
+
+  // A nested lambda might have parameters with immediate invocations
+  // in their default arguments.
+  // The compound statement is not visited (as it does not constitute a
+  // subexpression).
+  // FIXME: We should consider visiting and transforming captures
+  // with init expressions.
+  bool VisitLambdaExpr(LambdaExpr *E) {
+    return VisitCXXMethodDecl(E->getCallOperator());
+  }
+
+  // Blocks don't support default parameters, and, as for lambdas,
+  // we don't consider their body a subexpression.
+  bool VisitBlockDecl(BlockDecl *B) { return false; }
+
+  bool VisitCompoundStmt(CompoundStmt *B) { return false; }
+
+  bool VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
+    return TraverseStmt(E->getExpr());
+  }
+
+  bool VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
+    return TraverseStmt(E->getExpr());
+  }
+};
+
+struct EnsureImmediateInvocationInDefaultArgs
+    : TreeTransform<EnsureImmediateInvocationInDefaultArgs> {
+  EnsureImmediateInvocationInDefaultArgs(Sema &SemaRef)
+      : TreeTransform(SemaRef) {}
+
+  // Lambda can only have immediate invocations in the default
+  // args of their parameters, which is transformed upon calling the closure.
+  // The body is not a subexpression, so we have nothing to do.
+  // FIXME: Immediate calls in capture initializers should be transformed.
+  ExprResult TransformLambdaExpr(LambdaExpr *E) { return E; }
+  ExprResult TransformBlockExpr(BlockExpr *E) { return E; }
+};
+
 ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
-                                        FunctionDecl *FD, ParmVarDecl *Param) {
+                                        FunctionDecl *FD, ParmVarDecl *Param,
+                                        Expr *Init) {
   assert(Param->hasDefaultArg() && "can't build nonexistent default arg");
-  if (CheckCXXDefaultArgExpr(CallLoc, FD, Param))
+
+  bool NestedDefaultChecking =
+      isCheckingDefaultArgumentOrInitializerOfOuterEntity();
+
+  llvm::Optional<ExpressionEvaluationContextRecord::InitializationContext>
+      InitializationContext =
+          OutermostDeclarationWithDelayedImmediateInvocations();
+  if (!InitializationContext.has_value())
+    InitializationContext.emplace(CallLoc, Param, CurContext);
+
+  if (!Init && !Param->hasUnparsedDefaultArg()) {
+    // Mark that we are replacing a default argument first.
+    // If we are instantiating a template we won't have to
+    // retransform immediate calls.
+    EnterExpressionEvaluationContext EvalContext(
+        *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
+    ExprEvalContexts.back().DelayedDefaultInitializationContext = {
+        CallLoc, Param, CurContext};
+
+    if (Param->hasUninstantiatedDefaultArg()) {
+      if (InstantiateDefaultArgument(CallLoc, FD, Param))
+        return ExprError();
+    } else {
+      // CWG2631
+      // An immediate invocation that is not evaluated where it appears is
+      // evaluated and checked for whether it is a constant expression at the
+      // point where the enclosing initializer is used in a function call.
+      ImmediateCallVisitor V;
+      if (!NestedDefaultChecking)
+        V.TraverseDecl(Param);
+      if (V.HasImmediateCalls) {
+        EnsureImmediateInvocationInDefaultArgs Immediate(*this);
+        ExprResult Res = Immediate.TransformExpr(Param->getInit());
+        if (Res.isInvalid())
+          return ExprError();
+        Res = ConvertParamDefaultArgument(Param, Res.get(),
+                                          Res.get()->getBeginLoc());
+        if (Res.isInvalid())
+          return ExprError();
+        Init = Res.get();
+      }
+    }
+  }
+
+  if (CheckCXXDefaultArgExpr(
+          CallLoc, FD, Param, Init,
+          /*SkipImmediateInvocations=*/NestedDefaultChecking))
+    return ExprError();
+
+  return CXXDefaultArgExpr::Create(Context, InitializationContext->Loc, Param,
+                                   Init, InitializationContext->Context);
+}
+
+ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
+  assert(Field->hasInClassInitializer());
+
+  // If we might have already tried and failed to instantiate, don't try again.
+  if (Field->isInvalidDecl())
     return ExprError();
-  return CXXDefaultArgExpr::Create(Context, CallLoc, Param, CurContext);
+
+  auto *ParentRD = cast<CXXRecordDecl>(Field->getParent());
+
+  llvm::Optional<ExpressionEvaluationContextRecord::InitializationContext>
+      InitializationContext =
+          OutermostDeclarationWithDelayedImmediateInvocations();
+  if (!InitializationContext.has_value())
+    InitializationContext.emplace(Loc, Field, CurContext);
+
+  Expr *Init = nullptr;
+
+  bool NestedDefaultChecking =
+      isCheckingDefaultArgumentOrInitializerOfOuterEntity();
+
+  if (!Field->getInClassInitializer()) {
+    // Maybe we haven't instantiated the in-class initializer. Go check the
+    // pattern FieldDecl to see if it has one.
+    if (isTemplateInstantiation(ParentRD->getTemplateSpecializationKind())) {
+      CXXRecordDecl *ClassPattern = ParentRD->getTemplateInstantiationPattern();
+      DeclContext::lookup_result Lookup =
+          ClassPattern->lookup(Field->getDeclName());
+
+      FieldDecl *Pattern = nullptr;
+      for (auto *L : Lookup) {
+        if ((Pattern = dyn_cast<FieldDecl>(L)))
+          break;
+      }
+      assert(Pattern && "We must have set the Pattern!");
+      if (!Pattern->hasInClassInitializer() ||
+          InstantiateInClassInitializer(Loc, Field, Pattern,
+                                        getTemplateInstantiationArgs(Field))) {
+        Field->setInvalidDecl();
+        return ExprError();
+      }
+    }
+  } else {
+    // CWG2631
+    // An immediate invocation that is not evaluated where it appears is
+    // evaluated and checked for whether it is a constant expression at the
+    // point where the enclosing initializer is used in a [...] a constructor
+    // definition, or an aggregate initialization.
+    EnterExpressionEvaluationContext EvalContext(
+        *this, ExpressionEvaluationContext::PotentiallyEvaluated, Field);
+    ExprEvalContexts.back().DelayedDefaultInitializationContext = {Loc, Field,
+                                                                   CurContext};
+
+    ImmediateCallVisitor V;
+    if (!NestedDefaultChecking)
+      V.TraverseDecl(Field);
+    if (V.HasImmediateCalls) {
+      EnsureImmediateInvocationInDefaultArgs Immediate(*this);
+      ExprResult Res = Immediate.TransformExpr(Field->getInClassInitializer());
+      if (!Res.isInvalid())
+        Res = ConvertMemberDefaultInitExpression(Field, Res.get(), Loc);
+      if (Res.isInvalid()) {
+        Field->setInvalidDecl();
+        return ExprError();
+      }
+      Init = Res.get();
+    }
+  }
+
+  if (Field->getInClassInitializer()) {
+    Expr *E = Init ? Init : Field->getInClassInitializer();
+    if (!NestedDefaultChecking) {
+      EnterExpressionEvaluationContext EvalContext(
+          *this, ExpressionEvaluationContext::PotentiallyEvaluated, Field);
+      MarkDeclarationsReferencedInExpr(E, /*SkipLocalVariables=*/false);
+    }
+    // C++11 [class.base.init]p7:
+    //   The initialization of each base and member constitutes a
+    //   full-expression.
+    ExprResult Res = ActOnFinishFullExpr(E, /*DiscardedValue=*/false);
+    if (Res.isInvalid()) {
+      Field->setInvalidDecl();
+      return ExprError();
+    }
+    Init = Res.get();
+
+    return CXXDefaultInitExpr::Create(Context, InitializationContext->Loc,
+                                      Field, InitializationContext->Context,
+                                      Init);
+  }
+
+  // DR1351:
+  //   If the brace-or-equal-initializer of a non-static data member
+  //   invokes a defaulted default constructor of its class or of an
+  //   enclosing class in a potentially evaluated subexpression, the
+  //   program is ill-formed.
+  //
+  // This resolution is unworkable: the exception specification of the
+  // default constructor can be needed in an unevaluated context, in
+  // particular, in the operand of a noexcept-expression, and we can be
+  // unable to compute an exception specification for an enclosed class.
+  //
+  // Any attempt to resolve the exception specification of a defaulted default
+  // constructor before the initializer is lexically complete will ultimately
+  // come here at which point we can diagnose it.
+  RecordDecl *OutermostClass = ParentRD->getOuterLexicalRecordContext();
+  Diag(Loc, diag::err_default_member_initializer_not_yet_parsed)
+      << OutermostClass << Field;
+  Diag(Field->getEndLoc(),
+       diag::note_default_member_initializer_not_yet_parsed);
+  // Recover by marking the field invalid, unless we're in a SFINAE context.
+  if (!isSFINAEContext())
+    Field->setInvalidDecl();
+  return ExprError();
 }
 
 Sema::VariadicCallType
@@ -17541,6 +17762,7 @@ void Sema::CheckUnusedVolatileAssignment(Expr *E) {
 ExprResult Sema::CheckForImmediateInvocation(ExprResult E, FunctionDecl *Decl) {
   if (isUnevaluatedContext() || !E.isUsable() || !Decl ||
       !Decl->isConsteval() || isConstantEvaluated() ||
+      isCheckingDefaultArgumentOrInitializer() ||
       RebuildingImmediateInvocation || isImmediateFunctionContext())
     return E;
 
@@ -17586,8 +17808,14 @@ static void EvaluateAndDiagnoseImmediateInvocation(
       FD = Call->getConstructor();
     else
       llvm_unreachable("unhandled decl kind");
-    assert(FD->isConsteval());
+    assert(FD && FD->isConsteval());
     SemaRef.Diag(CE->getBeginLoc(), diag::err_invalid_consteval_call) << FD;
+    if (auto Context =
+            SemaRef.InnermostDeclarationWithDelayedImmediateInvocations()) {
+      SemaRef.Diag(Context->Loc, diag::note_invalid_consteval_initializer)
+          << Context->Decl;
+      SemaRef.Diag(Context->Decl->getBeginLoc(), diag::note_declared_at);
+    }
     for (auto &Note : Notes)
       SemaRef.Diag(Note.first, Note.second);
     return;
@@ -19733,7 +19961,8 @@ void Sema::MarkDeclRefReferenced(DeclRefExpr *E, const Expr *Base) {
 
   if (auto *FD = dyn_cast<FunctionDecl>(E->getDecl()))
     if (!isUnevaluatedContext() && !isConstantEvaluated() &&
-        !isImmediateFunctionContext() && FD->isConsteval() &&
+        !isImmediateFunctionContext() &&
+        !isCheckingDefaultArgumentOrInitializer() && FD->isConsteval() &&
         !RebuildingImmediateInvocation && !FD->isDependentContext())
       ExprEvalContexts.back().ReferenceToConsteval.insert(E);
   MarkExprReferenced(*this, E->getLocation(), E->getDecl(), E, OdrUse,

diff  --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 9e41dfbfdbe95..709162e01809b 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1978,9 +1978,9 @@ ExprResult TemplateInstantiator::TransformCXXDefaultArgExpr(
   assert(!cast<FunctionDecl>(E->getParam()->getDeclContext())->
              getDescribedFunctionTemplate() &&
          "Default arg expressions are never formed in dependent cases.");
-  return SemaRef.BuildCXXDefaultArgExpr(E->getUsedLocation(),
-                           cast<FunctionDecl>(E->getParam()->getDeclContext()),
-                                        E->getParam());
+  return SemaRef.BuildCXXDefaultArgExpr(
+      E->getUsedLocation(), cast<FunctionDecl>(E->getParam()->getDeclContext()),
+      E->getParam());
 }
 
 template<typename Fn>
@@ -3407,6 +3407,8 @@ bool Sema::InstantiateInClassInitializer(
   ContextRAII SavedContext(*this, Instantiation->getParent());
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+  ExprEvalContexts.back().DelayedDefaultInitializationContext = {
+      PointOfInstantiation, Instantiation, CurContext};
 
   LocalInstantiationScope Scope(*this, true);
 

diff  --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 019ea3efd1a6b..701ceb64cdbcf 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -3211,9 +3211,10 @@ class TreeTransform {
   /// By default, builds a new default-argument expression, which does not
   /// require any semantic analysis. Subclasses may override this routine to
   /// provide 
diff erent behavior.
-  ExprResult RebuildCXXDefaultArgExpr(SourceLocation Loc, ParmVarDecl *Param) {
+  ExprResult RebuildCXXDefaultArgExpr(SourceLocation Loc, ParmVarDecl *Param,
+                                      Expr *RewrittenExpr) {
     return CXXDefaultArgExpr::Create(getSema().Context, Loc, Param,
-                                     getSema().CurContext);
+                                     RewrittenExpr, getSema().CurContext);
   }
 
   /// Build a new C++11 default-initialization expression.
@@ -3223,8 +3224,7 @@ class TreeTransform {
   /// routine to provide 
diff erent behavior.
   ExprResult RebuildCXXDefaultInitExpr(SourceLocation Loc,
                                        FieldDecl *Field) {
-    return CXXDefaultInitExpr::Create(getSema().Context, Loc, Field,
-                                      getSema().CurContext);
+    return getSema().BuildCXXDefaultInitExpr(Loc, Field);
   }
 
   /// Build a new C++ zero-initialization expression.
@@ -12161,11 +12161,20 @@ TreeTransform<Derived>::TransformCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
   if (!Param)
     return ExprError();
 
+  ExprResult InitRes;
+  if (E->hasRewrittenInit()) {
+    InitRes = getDerived().TransformExpr(E->getRewrittenExpr());
+    if (InitRes.isInvalid())
+      return ExprError();
+  }
+
   if (!getDerived().AlwaysRebuild() && Param == E->getParam() &&
-      E->getUsedContext() == SemaRef.CurContext)
+      E->getUsedContext() == SemaRef.CurContext &&
+      InitRes.get() == E->getRewrittenExpr())
     return E;
 
-  return getDerived().RebuildCXXDefaultArgExpr(E->getUsedLocation(), Param);
+  return getDerived().RebuildCXXDefaultArgExpr(E->getUsedLocation(), Param,
+                                               InitRes.get());
 }
 
 template<typename Derived>

diff  --git a/clang/lib/Serialization/ASTReaderStmt.cpp b/clang/lib/Serialization/ASTReaderStmt.cpp
index 2a3c6e7231785..08f9f0bf50d03 100644
--- a/clang/lib/Serialization/ASTReaderStmt.cpp
+++ b/clang/lib/Serialization/ASTReaderStmt.cpp
@@ -1824,6 +1824,9 @@ void ASTStmtReader::VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
   E->Param = readDeclAs<ParmVarDecl>();
   E->UsedContext = readDeclAs<DeclContext>();
   E->CXXDefaultArgExprBits.Loc = readSourceLocation();
+  E->CXXDefaultArgExprBits.HasRewrittenInit = Record.readInt();
+  if (E->CXXDefaultArgExprBits.HasRewrittenInit)
+    *E->getTrailingObjects<Expr *>() = Record.readSubExpr();
 }
 
 void ASTStmtReader::VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
@@ -1831,6 +1834,9 @@ void ASTStmtReader::VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
   E->Field = readDeclAs<FieldDecl>();
   E->UsedContext = readDeclAs<DeclContext>();
   E->CXXDefaultInitExprBits.Loc = readSourceLocation();
+  E->CXXDefaultInitExprBits.HasRewrittenInit = Record.readInt();
+  if (E->CXXDefaultInitExprBits.HasRewrittenInit)
+    *E->getTrailingObjects<Expr *>() = Record.readSubExpr();
 }
 
 void ASTStmtReader::VisitCXXBindTemporaryExpr(CXXBindTemporaryExpr *E) {
@@ -3829,11 +3835,13 @@ Stmt *ASTReader::ReadStmtFromStream(ModuleFile &F) {
       break;
 
     case EXPR_CXX_DEFAULT_ARG:
-      S = new (Context) CXXDefaultArgExpr(Empty);
+      S = CXXDefaultArgExpr::CreateEmpty(
+          Context, /*HasRewrittenInit=*/Record[ASTStmtReader::NumExprFields]);
       break;
 
     case EXPR_CXX_DEFAULT_INIT:
-      S = new (Context) CXXDefaultInitExpr(Empty);
+      S = CXXDefaultInitExpr::CreateEmpty(
+          Context, /*HasRewrittenInit=*/Record[ASTStmtReader::NumExprFields]);
       break;
 
     case EXPR_CXX_BIND_TEMPORARY:

diff  --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
index e2ba69ca1eec8..6e4101ac122ee 100644
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -1745,6 +1745,9 @@ void ASTStmtWriter::VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
   Record.AddDeclRef(E->getParam());
   Record.AddDeclRef(cast_or_null<Decl>(E->getUsedContext()));
   Record.AddSourceLocation(E->getUsedLocation());
+  Record.push_back(E->hasRewrittenInit());
+  if (E->hasRewrittenInit())
+    Record.AddStmt(E->getRewrittenExpr());
   Code = serialization::EXPR_CXX_DEFAULT_ARG;
 }
 
@@ -1753,6 +1756,9 @@ void ASTStmtWriter::VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
   Record.AddDeclRef(E->getField());
   Record.AddDeclRef(cast_or_null<Decl>(E->getUsedContext()));
   Record.AddSourceLocation(E->getExprLoc());
+  Record.push_back(E->hasRewrittenInit());
+  if (E->hasRewrittenInit())
+    Record.AddStmt(E->getRewrittenExpr());
   Code = serialization::EXPR_CXX_DEFAULT_INIT;
 }
 

diff  --git a/clang/test/CXX/class/class.local/p1-0x.cpp b/clang/test/CXX/class/class.local/p1-0x.cpp
index 49125f5f9b062..096f5080099ec 100644
--- a/clang/test/CXX/class/class.local/p1-0x.cpp
+++ b/clang/test/CXX/class/class.local/p1-0x.cpp
@@ -11,8 +11,8 @@ void f() {
     int x = 3; // expected-note{{'x' declared here}}
     struct C {
       int& x2 = x; // expected-error{{reference to local variable 'x' declared in enclosing lambda expression}}
-    };
+    }c; // expected-note {{required here}}
   };
-  C();
+  C(); // expected-note {{required here}}
 }
 

diff  --git a/clang/test/CXX/drs/dr26xx.cpp b/clang/test/CXX/drs/dr26xx.cpp
index 6aa0e5053bc9a..68a0e9b2a2688 100644
--- a/clang/test/CXX/drs/dr26xx.cpp
+++ b/clang/test/CXX/drs/dr26xx.cpp
@@ -88,3 +88,19 @@ void f() {
     brachiosaur |= neck;                // OK
 }
 }
+
+namespace dr2631 { // dr2631: 16
+  constexpr int g();
+  consteval int f() {
+    return g();
+  }
+  int k(int x = f()) {
+    return x;
+  }
+  constexpr int g() {
+    return 42;
+  }
+  int test() {
+    return k();
+  }
+}

diff  --git a/clang/test/CodeGenCXX/builtin-source-location.cpp b/clang/test/CodeGenCXX/builtin-source-location.cpp
index 6e44e6b0e60e3..7af6749d0d6d6 100644
--- a/clang/test/CodeGenCXX/builtin-source-location.cpp
+++ b/clang/test/CodeGenCXX/builtin-source-location.cpp
@@ -1,4 +1,6 @@
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++2a -fblocks %s -triple x86_64-unknown-unknown -emit-llvm -o %t.ll
+// RUN: %clang_cc1 -no-opaque-pointers -std=c++14 -fblocks %s -triple x86_64-unknown-unknown -emit-llvm -o %t.ll
+
 
 // This needs to be performed before #line directives which alter filename
 // RUN: %clang_cc1 -no-opaque-pointers -fno-file-reproducible -fmacro-prefix-map=%p=/UNLIKELY/PATH -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-PREFIX-MAP

diff  --git a/clang/test/CodeGenCXX/default-arguments-with-immediate.cpp b/clang/test/CodeGenCXX/default-arguments-with-immediate.cpp
new file mode 100644
index 0000000000000..54a02ffc06836
--- /dev/null
+++ b/clang/test/CodeGenCXX/default-arguments-with-immediate.cpp
@@ -0,0 +1,54 @@
+// RUN: %clang_cc1 -std=c++2a -triple x86_64-elf-gnu %s -emit-llvm -o - | FileCheck %s
+
+consteval int immediate() { return 0;}
+static int ext();
+void f(int a = immediate() + ext());
+
+void test_function() {
+    f();
+    f(0);
+    // CHECK: call noundef i32 @_ZL3extv()
+    // CHECK: add
+    // CHECK: call {{.*}} @_Z1fi
+    // CHECK: call {{.*}} @_Z1fi
+}
+
+// CHECK: define {{.*}} i32 @_ZL3extv()
+
+static constexpr int not_immediate();
+struct A {
+    int a = immediate() + not_immediate();
+};
+
+void test_member() {
+    // CHECK: call void @_ZN1AC2Ev
+    A defaulted;
+    // CHECK-NOT: call void @_ZN1AC2Ev
+    A provided{0};
+}
+
+// CHECK: define {{.*}} void @_ZN1AC2Ev{{.*}}
+// CHECK: %call = call noundef i32 @_ZL13not_immediatev()
+
+int never_referenced() {return 42;};
+
+
+namespace not_used {
+
+struct A {
+    int a = immediate() + never_referenced();
+};
+void f(int a = immediate() + never_referenced());
+
+void g() {
+    A a{0};
+    f(0);
+}
+
+}
+
+static int ext() {return 0;}
+static constexpr int not_immediate() {return 0;}
+
+// CHECK-NOT: define {{.*}} i32 _ZL16never_referencedv()(
+// CHECK: define {{.*}} i32 @_ZL13not_immediatev()

diff  --git a/clang/test/PCH/default-argument-with-immediate-calls.cpp b/clang/test/PCH/default-argument-with-immediate-calls.cpp
new file mode 100644
index 0000000000000..510605a23d4e7
--- /dev/null
+++ b/clang/test/PCH/default-argument-with-immediate-calls.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -std=c++20 -emit-pch %s -o %t
+// RUN: %clang_cc1 -std=c++20 -include-pch %t -verify %s
+// expected-no-diagnostics
+
+#ifndef HEADER_INCLUDED
+#define HEADER_INCLUDED
+
+consteval int immediate();
+int regular_function() {
+    return 0;
+}
+
+struct S {
+  int a = immediate() + regular_function();
+};
+
+int f(int arg = immediate()) {
+    return arg;
+}
+
+#else
+
+consteval int immediate() {
+    return 0;
+}
+
+void test() {
+    f(0);
+    f();
+    S s{0};
+    S t{0};
+}
+
+#endif

diff  --git a/clang/test/SemaCXX/cxx11-default-member-initializers.cpp b/clang/test/SemaCXX/cxx11-default-member-initializers.cpp
index 9353e633fafbc..d32ff48bf0ce0 100644
--- a/clang/test/SemaCXX/cxx11-default-member-initializers.cpp
+++ b/clang/test/SemaCXX/cxx11-default-member-initializers.cpp
@@ -12,3 +12,13 @@ namespace PR31692 {
   // A::X can now be default-constructed.
   static_assert(__is_constructible(A::X), "");
 }
+
+
+struct S {
+} constexpr s;
+struct C {
+  C(S);
+};
+class MemInit {
+  C m = s;
+};

diff  --git a/clang/test/SemaCXX/cxx2a-consteval-default-params.cpp b/clang/test/SemaCXX/cxx2a-consteval-default-params.cpp
new file mode 100644
index 0000000000000..abeb27fd03e35
--- /dev/null
+++ b/clang/test/SemaCXX/cxx2a-consteval-default-params.cpp
@@ -0,0 +1,81 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++2b %s
+
+consteval int undefined();  // expected-note 4 {{declared here}}
+
+void check_lambdas_unused(
+    int a = []
+    {
+        // The body of a lambda is not a subexpression of the lambda
+        // so this is immediately evaluated even if the parameter
+        // is never used.
+        return undefined();  // expected-error {{not a constant expression}} \
+                             // expected-note  {{undefined function 'undefined'}}
+    }(),
+    int b = [](int no_error = undefined()) {
+        return no_error;
+    }(0),
+    int c = [](int defaulted = undefined()) {
+        return defaulted;
+    }()
+) {}
+
+int check_lambdas_used(
+    int b = [](int no_error = undefined()) {
+        return no_error;
+    }(0),
+    int c = [](int defaulted = undefined()) { // expected-error {{not a constant expression}} \
+                              // expected-note  {{declared here}} \
+                              // expected-note  {{undefined function 'undefined'}}
+        return defaulted;
+    }(),  // expected-note {{in the default initalizer of 'defaulted'}}
+    int d = [](int defaulted = sizeof(undefined())) {
+        return defaulted;
+    }()
+) {
+    return 0;
+}
+
+int test_check_lambdas_used = check_lambdas_used();
+
+struct UnusedInitWithLambda {
+    int a = [] {
+        return undefined();  // expected-error {{not a constant expression}} \
+                             // expected-note  {{undefined function 'undefined'}}
+    }();
+    // UnusedInitWithLambda is never constructed, so the initializer
+    // of b and undefined() are never evaluated.
+    int b = [](int no_error = undefined()) {
+        return no_error;
+    }();
+};
+
+consteval int ub(int n) {
+    return 0/n; // expected-note  {{division}}
+}
+
+struct InitWithLambda {
+    int b = [](int error = undefined()) { // expected-error {{not a constant expression}} \
+                              // expected-note  {{declared here}} \
+                              // expected-note  {{undefined function 'undefined'}}
+        return error;
+    }(); // expected-note {{in the default initalizer of 'error'}}
+    int c = [](int error = sizeof(undefined()) + ub(0)) { // expected-error {{'ub' is not a constant expression}} \
+                                                          // expected-note  {{declared here}} \
+                                                          // expected-note {{in call to 'ub(0)}}
+        return error;
+    }(); // expected-note {{in the default initalizer of 'error'}}
+} i; // expected-note {{in implicit default constructor}}
+
+namespace ShouldNotCrash {
+    template<typename T>
+    struct F {
+        template<typename U>
+        F(const U&) {}
+    };
+    struct A {
+        static constexpr auto x = [] {};
+        F<int> f = x;
+    };
+    void f(A a = A()) { }
+}

diff  --git a/clang/test/SemaCXX/source_location.cpp b/clang/test/SemaCXX/source_location.cpp
index ccb385f60dc4b..9cfe9207dd14d 100644
--- a/clang/test/SemaCXX/source_location.cpp
+++ b/clang/test/SemaCXX/source_location.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify %s
+// RUN: %clang_cc1 -std=c++2a -fcxx-exceptions -DUSE_CONSTEVAL -fexceptions -verify %s
 // expected-no-diagnostics
 
 #define assert(...) ((__VA_ARGS__) ? ((void)0) : throw 42)
@@ -8,15 +9,22 @@
 template <unsigned>
 struct Printer;
 
+#ifdef USE_CONSTEVAL
+#define SOURCE_LOC_EVAL_KIND consteval
+#else
+#define SOURCE_LOC_EVAL_KIND constexpr
+#endif
+
 namespace std {
 class source_location {
   struct __impl;
 
 public:
-  static constexpr source_location current(const __impl *__p = __builtin_source_location()) noexcept {
-    source_location __loc;
-    __loc.__m_impl = __p;
-    return __loc;
+  static SOURCE_LOC_EVAL_KIND source_location
+    current(const __impl *__p = __builtin_source_location()) noexcept {
+      source_location __loc;
+      __loc.__m_impl = __p;
+      return __loc;
   }
   constexpr source_location() = default;
   constexpr source_location(source_location const &) = default;
@@ -593,3 +601,51 @@ namespace TestConstexprContext {
   }
   static_assert(test());
 }
+
+namespace Lambda {
+#line 8000 "TestLambda.cpp"
+constexpr int nested_lambda(int l = []{
+  return SL::current().line();
+}()) {
+  return l;
+}
+static_assert(nested_lambda() == __LINE__ - 4);
+
+constexpr int lambda_param(int l = [](int l = SL::current().line()) {
+  return l;
+}()) {
+  return l;
+}
+static_assert(lambda_param() == __LINE__);
+
+
+}
+
+constexpr int compound_literal_fun(int a =
+                  (int){ SL::current().line() }
+) { return a ;}
+static_assert(compound_literal_fun() == __LINE__);
+
+struct CompoundLiteral {
+  int a = (int){ SL::current().line() };
+};
+static_assert(CompoundLiteral{}.a == __LINE__);
+
+
+// FIXME
+// Init captures are subexpressions of the lambda expression
+// so according to the standard immediate invocations in init captures
+// should be evaluated at the call site.
+// However Clang does not yet implement this as it would introduce
+// a fair bit of complexity.
+// We intend to implement that functionality once we find real world
+// use cases that require it.
+constexpr int test_init_capture(int a =
+                [b = SL::current().line()] { return b; }()) {
+  return a;
+}
+#ifdef USE_CONSTEVAL
+static_assert(test_init_capture() == __LINE__ - 4);
+#else
+static_assert(test_init_capture() == __LINE__ );
+#endif

diff  --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index cec9fe58cf601..6d020f05b489a 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -15594,7 +15594,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://wg21.link/cwg2631">2631</a></td>
     <td>DR</td>
     <td>Immediate function evaluations in default arguments</td>
-    <td class="none" align="center">Unknown</td>
+    <td class="unreleased" align="center">Clang 16</td>
   </tr>
   <tr class="open" id="2632">
     <td><a href="https://wg21.link/cwg2632">2632</a></td>


        


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