https://github.com/zmodem created 
https://github.com/llvm/llvm-project/pull/203554

This is for https://github.com/llvm/llvm-project/issues/201320

Just grabbing the default argument with `getDefaultArg()` during codegen 
doesn't work if the expression requires evaluating a consteval expression (see 
bug). Instead, we must properly BuildCXXDefaultArgExpr it during Sema, store it 
in the AST (including serializatin/deserialization) and then use that during 
codegen.

>From 43f8ddc6e8bf4ac120c9a3f5e1142ab2cdc32d46 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 13:26:00 +0200
Subject: [PATCH 1/8] InstantiateDefaultCtorDefaultArgs ->
 BuildDefaultArgsForCtorClosure and move to SemaDeclCXX.cpp

---
 clang/include/clang/Sema/Sema.h               |  7 ++-----
 clang/lib/Sema/SemaDecl.cpp                   |  2 +-
 clang/lib/Sema/SemaDeclCXX.cpp                | 19 ++++++++++++++++++-
 .../lib/Sema/SemaTemplateInstantiateDecl.cpp  | 18 +-----------------
 4 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index b8d760e7e0975..4b972d8bf0516 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -14265,11 +14265,8 @@ class Sema final : public SemaBase {
                           LateInstantiatedAttrVec *LateAttrs = nullptr,
                           LocalInstantiationScope *OuterMostScope = nullptr);
 
-  /// In the MS ABI, we need to instantiate default arguments of dllexported
-  /// default constructors along with the constructor definition. This allows 
IR
-  /// gen to emit a constructor closure which calls the default constructor 
with
-  /// its default arguments.
-  void InstantiateDefaultCtorDefaultArgs(CXXConstructorDecl *Ctor);
+  /// XXX: comment
+  void BuildDefaultArgsForCtorClosure(CXXConstructorDecl *Ctor);
 
   bool InstantiateDefaultArgument(SourceLocation CallLoc, FunctionDecl *FD,
                                   ParmVarDecl *Param);
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index cddcf3a010279..2255d6141db1e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16306,7 +16306,7 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, 
Decl *D,
         Context.getTargetInfo().getCXXABI().isMicrosoft()) {
       // If this is an MS ABI dllexport default constructor, instantiate any
       // default arguments.
-      InstantiateDefaultCtorDefaultArgs(Ctor);
+      BuildDefaultArgsForCtorClosure(Ctor);
     }
   }
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 418ff01f3d98a..f583a765863a4 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -6339,7 +6339,7 @@ static void ReferenceDllExportedMembers(Sema &S, 
CXXRecordDecl *Class) {
       if (S.Context.getTargetInfo().getCXXABI().isMicrosoft()) {
         auto *CD = dyn_cast<CXXConstructorDecl>(MD);
         if (CD && CD->isDefaultConstructor() && TSK == TSK_Undeclared) {
-          S.InstantiateDefaultCtorDefaultArgs(CD);
+          S.BuildDefaultArgsForCtorClosure(CD);
         }
       }
 
@@ -19804,3 +19804,20 @@ void 
Sema::ActOnFinishFunctionDeclarationDeclarator(Declarator &Declarator) {
   }
   InventedParameterInfos.pop_back();
 }
+
+void Sema::BuildDefaultArgsForCtorClosure(CXXConstructorDecl *Ctor) {
+  assert(Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+         Ctor->isDefaultConstructor());
+  unsigned NumParams = Ctor->getNumParams();
+  if (NumParams == 0)
+    return;
+  DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
+  if (!Attr)
+    return;
+  for (unsigned I = 0; I != NumParams; ++I) {
+    (void)CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
+                                   Ctor->getParamDecl(I));
+    CleanupVarDeclMarking();
+  }
+
+}
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp 
b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 324d6bf3857c7..26ccde0d3315d 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1078,22 +1078,6 @@ void Sema::updateAttrsForLateParsedTemplate(const Decl 
*Pattern, Decl *Inst) {
   }
 }
 
-void Sema::InstantiateDefaultCtorDefaultArgs(CXXConstructorDecl *Ctor) {
-  assert(Context.getTargetInfo().getCXXABI().isMicrosoft() &&
-         Ctor->isDefaultConstructor());
-  unsigned NumParams = Ctor->getNumParams();
-  if (NumParams == 0)
-    return;
-  DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
-  if (!Attr)
-    return;
-  for (unsigned I = 0; I != NumParams; ++I) {
-    (void)CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
-                                   Ctor->getParamDecl(I));
-    CleanupVarDeclMarking();
-  }
-}
-
 /// Get the previous declaration of a declaration for the purposes of template
 /// instantiation. If this finds a previous declaration, then the previous
 /// declaration of the instantiation of D should be an instantiation of the
@@ -5961,7 +5945,7 @@ void Sema::InstantiateFunctionDefinition(SourceLocation 
PointOfInstantiation,
         // default arguments.
         if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
             Ctor->isDefaultConstructor()) {
-          InstantiateDefaultCtorDefaultArgs(Ctor);
+          BuildDefaultArgsForCtorClosure(Ctor);
         }
       }
 

>From 9d30dda8251346958fc6af3df120af53f0cabd79 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 14:08:37 +0200
Subject: [PATCH 2/8] add Loc and IsCopy params, use it for
 CheckCXXThrowOperand too

---
 clang/include/clang/Sema/Sema.h               |  2 +-
 clang/lib/Sema/SemaDecl.cpp                   |  3 ++-
 clang/lib/Sema/SemaDeclCXX.cpp                | 24 +++++++++----------
 clang/lib/Sema/SemaExprCXX.cpp                |  7 +++---
 .../lib/Sema/SemaTemplateInstantiateDecl.cpp  |  3 ++-
 5 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 4b972d8bf0516..84a124aa076fe 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -14266,7 +14266,7 @@ class Sema final : public SemaBase {
                           LocalInstantiationScope *OuterMostScope = nullptr);
 
   /// XXX: comment
-  void BuildDefaultArgsForCtorClosure(CXXConstructorDecl *Ctor);
+  bool BuildDefaultArgsForCtorClosure(SourceLocation Loc, CXXConstructorDecl 
*Ctor, bool IsCopy = false);
 
   bool InstantiateDefaultArgument(SourceLocation CallLoc, FunctionDecl *FD,
                                   ParmVarDecl *Param);
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 2255d6141db1e..67b91609fb609 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16306,7 +16306,8 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, 
Decl *D,
         Context.getTargetInfo().getCXXABI().isMicrosoft()) {
       // If this is an MS ABI dllexport default constructor, instantiate any
       // default arguments.
-      BuildDefaultArgsForCtorClosure(Ctor);
+      if (DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>())
+        BuildDefaultArgsForCtorClosure(Attr->getLocation(), Ctor);
     }
   }
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index f583a765863a4..9b8ad2390a60a 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -6339,7 +6339,7 @@ static void ReferenceDllExportedMembers(Sema &S, 
CXXRecordDecl *Class) {
       if (S.Context.getTargetInfo().getCXXABI().isMicrosoft()) {
         auto *CD = dyn_cast<CXXConstructorDecl>(MD);
         if (CD && CD->isDefaultConstructor() && TSK == TSK_Undeclared) {
-          S.BuildDefaultArgsForCtorClosure(CD);
+          
S.BuildDefaultArgsForCtorClosure(CD->getAttr<DLLExportAttr>()->getLocation(), 
CD);
         }
       }
 
@@ -19805,19 +19805,19 @@ void 
Sema::ActOnFinishFunctionDeclarationDeclarator(Declarator &Declarator) {
   InventedParameterInfos.pop_back();
 }
 
-void Sema::BuildDefaultArgsForCtorClosure(CXXConstructorDecl *Ctor) {
-  assert(Context.getTargetInfo().getCXXABI().isMicrosoft() &&
-         Ctor->isDefaultConstructor());
+bool Sema::BuildDefaultArgsForCtorClosure(SourceLocation Loc, 
CXXConstructorDecl *Ctor, bool IsCopy) {
+  assert(Context.getTargetInfo().getCXXABI().isMicrosoft());
+
   unsigned NumParams = Ctor->getNumParams();
   if (NumParams == 0)
-    return;
-  DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
-  if (!Attr)
-    return;
-  for (unsigned I = 0; I != NumParams; ++I) {
-    (void)CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
-                                   Ctor->getParamDecl(I));
-    CleanupVarDeclMarking();
+    return false;
+
+  unsigned FirstParam = IsCopy ? 1 : 0;
+  for (unsigned I = FirstParam; I != NumParams; ++I) {
+    if (CheckCXXDefaultArgExpr(Loc, Ctor, Ctor->getParamDecl(I)))
+      return true;
+    CleanupVarDeclMarking(); // XXX: still not sure what this does.
   }
 
+  return false;
 }
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 4e1652462b3ae..59e69314c2803 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1070,10 +1070,9 @@ bool Sema::CheckCXXThrowOperand(SourceLocation ThrowLoc,
 
       // We don't keep the instantiated default argument expressions around so
       // we must rebuild them here.
-      for (unsigned I = 1, E = CD->getNumParams(); I != E; ++I) {
-        if (CheckCXXDefaultArgExpr(ThrowLoc, CD, CD->getParamDecl(I)))
-          return true;
-      }
+      // XXX: surprisingly, CD->isCopyConstructor() is not necessarily true 
here!
+      if (BuildDefaultArgsForCtorClosure(ThrowLoc, CD, /*IsCopy=*/true))
+        return true;
     }
   }
 
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp 
b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 26ccde0d3315d..9d21d5f96b020 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5945,7 +5945,8 @@ void Sema::InstantiateFunctionDefinition(SourceLocation 
PointOfInstantiation,
         // default arguments.
         if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
             Ctor->isDefaultConstructor()) {
-          BuildDefaultArgsForCtorClosure(Ctor);
+          if (DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>())
+            BuildDefaultArgsForCtorClosure(Attr->getLocation(), Ctor);
         }
       }
 

>From 89391825c88f8b0abf97f5982fde3cf57a994520 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 14:31:21 +0200
Subject: [PATCH 3/8] found one more caller; also use BuildCXXDefaultArgExpr
 now instead of CheckCXXDefaultArgExpr

---
 clang/lib/Sema/SemaDeclCXX.cpp | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 9b8ad2390a60a..9de72e94e9ec4 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -6392,10 +6392,8 @@ static void 
checkForMultipleExportedDefaultConstructors(Sema &S,
     // If the class is non-dependent, mark the default arguments as ODR-used so
     // that we can properly codegen the constructor closure.
     if (!Class->isDependentContext()) {
-      for (ParmVarDecl *PD : CD->parameters()) {
-        (void)S.CheckCXXDefaultArgExpr(Attr->getLocation(), CD, PD);
-        S.DiscardCleanupsInEvaluationContext();
-      }
+      S.BuildDefaultArgsForCtorClosure(Attr->getLocation(), CD);
+      S.DiscardCleanupsInEvaluationContext();
     }
 
     if (LastExportedDefaultCtor) {
@@ -19814,9 +19812,11 @@ bool 
Sema::BuildDefaultArgsForCtorClosure(SourceLocation Loc, CXXConstructorDecl
 
   unsigned FirstParam = IsCopy ? 1 : 0;
   for (unsigned I = FirstParam; I != NumParams; ++I) {
-    if (CheckCXXDefaultArgExpr(Loc, Ctor, Ctor->getParamDecl(I)))
+    ExprResult R = BuildCXXDefaultArgExpr(Loc, Ctor, Ctor->getParamDecl(I));
+    if (R.isInvalid())
       return true;
-    CleanupVarDeclMarking(); // XXX: still not sure what this does.
+
+    CleanupVarDeclMarking();
   }
 
   return false;

>From e31da8826f11801af71568cfbf30548c3560f1c2 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 14:51:49 +0200
Subject: [PATCH 4/8] start adding it to the ast

---
 clang/include/clang/AST/DeclCXX.h |  5 +++++
 clang/lib/Sema/SemaDeclCXX.cpp    | 12 +++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/clang/include/clang/AST/DeclCXX.h 
b/clang/include/clang/AST/DeclCXX.h
index cc4b4ff9db273..ba9036ef65157 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -2668,6 +2668,11 @@ class CXXConstructorDecl final
   friend class ASTDeclWriter;
   friend TrailingObjects;
 
+  // FIXME: Just hacking it in here for now.
+  Expr **CtorClosureArgs = nullptr;
+  Expr **ctorClosureArgs() const { return CtorClosureArgs; }
+  void setCtorClosureArgs(Expr **Args) { CtorClosureArgs = Args; }
+
   static CXXConstructorDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID,
                                                 uint64_t AllocKind);
   static CXXConstructorDecl *
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 9de72e94e9ec4..8b2286bbd0d23 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -19806,18 +19806,24 @@ void 
Sema::ActOnFinishFunctionDeclarationDeclarator(Declarator &Declarator) {
 bool Sema::BuildDefaultArgsForCtorClosure(SourceLocation Loc, 
CXXConstructorDecl *Ctor, bool IsCopy) {
   assert(Context.getTargetInfo().getCXXABI().isMicrosoft());
 
+  if (Ctor->ctorClosureArgs())
+    return false;
+
   unsigned NumParams = Ctor->getNumParams();
   if (NumParams == 0)
     return false;
-
   unsigned FirstParam = IsCopy ? 1 : 0;
+
+  Expr **Args = new (getASTContext()) Expr*[NumParams - FirstParam];
+
   for (unsigned I = FirstParam; I != NumParams; ++I) {
     ExprResult R = BuildCXXDefaultArgExpr(Loc, Ctor, Ctor->getParamDecl(I));
+    CleanupVarDeclMarking();
     if (R.isInvalid())
       return true;
-
-    CleanupVarDeclMarking();
+    Args[I - FirstParam] = R.get();
   }
+  Ctor->setCtorClosureArgs(Args);
 
   return false;
 }

>From decee090a0bfba3e476970a94b920df44917af17 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 15:48:42 +0200
Subject: [PATCH 5/8] serialize/deserialize the CtorClosureArgs

---
 clang/lib/Sema/SemaDeclCXX.cpp            | 5 +++--
 clang/lib/Serialization/ASTReaderDecl.cpp | 6 ++++++
 clang/lib/Serialization/ASTWriterDecl.cpp | 8 ++++++++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 8b2286bbd0d23..e7a96ad1f390c 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -19814,14 +19814,15 @@ bool 
Sema::BuildDefaultArgsForCtorClosure(SourceLocation Loc, CXXConstructorDecl
     return false;
   unsigned FirstParam = IsCopy ? 1 : 0;
 
-  Expr **Args = new (getASTContext()) Expr*[NumParams - FirstParam];
+  Expr **Args = new (getASTContext()) Expr*[NumParams];
+  Args[0] = nullptr;
 
   for (unsigned I = FirstParam; I != NumParams; ++I) {
     ExprResult R = BuildCXXDefaultArgExpr(Loc, Ctor, Ctor->getParamDecl(I));
     CleanupVarDeclMarking();
     if (R.isInvalid())
       return true;
-    Args[I - FirstParam] = R.get();
+    Args[I] = R.get();
   }
   Ctor->setCtorClosureArgs(Args);
 
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp 
b/clang/lib/Serialization/ASTReaderDecl.cpp
index fb291a4b0f2c5..8250b5bdec623 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2333,6 +2333,12 @@ void 
ASTDeclReader::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
     *D->getTrailingObjects<InheritedConstructor>() =
         InheritedConstructor(Shadow, Ctor);
   }
+  if (int NumCtorClosureArgs = Record.readInt()) {
+    Expr **Args = new (Reader.getContext()) Expr*[NumCtorClosureArgs];
+    for (int I = 0; I != NumCtorClosureArgs; I++)
+      Args[I] = cast<Expr>(Record.readStmt());
+    D->setCtorClosureArgs(Args);
+  }
 
   VisitCXXMethodDecl(D);
 }
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp 
b/clang/lib/Serialization/ASTWriterDecl.cpp
index 7f5005aa666c7..2ca34561b18a5 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1774,6 +1774,14 @@ void 
ASTDeclWriter::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
     Record.AddDeclRef(Inherited.getConstructor());
   }
 
+  if (Expr **CtorClosureArgs = D->ctorClosureArgs()) {
+    Record.push_back(D->getNumParams());
+    for (unsigned I = 0, N = D->getNumParams(); I != N; ++I)
+      Record.AddStmt(CtorClosureArgs[I]);
+  } else {
+    Record.push_back(0);
+  }
+
   VisitCXXMethodDecl(D);
   Code = serialization::DECL_CXX_CONSTRUCTOR;
 }

>From ff475437ab1d81574b333ed7ab7fae3361571d51 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 16:20:19 +0200
Subject: [PATCH 6/8] use ctorClosureArgs() in getAddrOfCXXCtorClosure()

---
 clang/lib/CodeGen/MicrosoftCXXABI.cpp | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp 
b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 40c7c00d85395..3de3fd8cbe3c8 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -4207,18 +4207,19 @@ MicrosoftCXXABI::getAddrOfCXXCtorClosure(const 
CXXConstructorDecl *CD,
   if (SrcVal)
     Args.add(RValue::get(SrcVal), SrcParam->getType());
 
+
   // Add the rest of the default arguments.
   SmallVector<const Stmt *, 4> ArgVec;
-  ArrayRef<ParmVarDecl *> params = CD->parameters().drop_front(IsCopy ? 1 : 0);
-  for (const ParmVarDecl *PD : params) {
-    assert(PD->hasDefaultArg() && "ctor closure lacks default args");
-    ArgVec.push_back(PD->getDefaultArg());
+  for (unsigned I = IsCopy ? 1 : 0, N = CD->getNumParams(); I != N; ++I) {
+    assert(CD->getParamDecl(I)->hasDefaultArg() && "ctor closure lacks default 
args");
+    assert(CD->ctorClosureArgs());
+    ArgVec.push_back(CD->ctorClosureArgs()[I]);
   }
 
   CodeGenFunction::RunCleanupsScope Cleanups(CGF);
 
   const auto *FPT = CD->getType()->castAs<FunctionProtoType>();
-  CGF.EmitCallArgs(Args, FPT, llvm::ArrayRef(ArgVec), CD, IsCopy ? 1 : 0);
+  CGF.EmitCallArgs(Args, FPT, ArrayRef(ArgVec), CD, IsCopy ? 1 : 0);
 
   // Insert any ABI-specific implicit constructor arguments.
   AddedStructorArgCounts ExtraArgs =

>From 935c664f56b5ea8da11e883fbbc41434838c31fd Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 16:25:00 +0200
Subject: [PATCH 7/8] gotta use the canonical ctor decl

---
 clang/include/clang/AST/DeclCXX.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/clang/include/clang/AST/DeclCXX.h 
b/clang/include/clang/AST/DeclCXX.h
index ba9036ef65157..e22881556e2a3 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -2670,8 +2670,8 @@ class CXXConstructorDecl final
 
   // FIXME: Just hacking it in here for now.
   Expr **CtorClosureArgs = nullptr;
-  Expr **ctorClosureArgs() const { return CtorClosureArgs; }
-  void setCtorClosureArgs(Expr **Args) { CtorClosureArgs = Args; }
+  Expr **ctorClosureArgs() const { return getCanonicalDecl()->CtorClosureArgs; 
}
+  void setCtorClosureArgs(Expr **Args) { getCanonicalDecl()->CtorClosureArgs = 
Args; }
 
   static CXXConstructorDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID,
                                                 uint64_t AllocKind);

>From 4461dec7f77f2084b00f089e61e951f96ed42453 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <[email protected]>
Date: Fri, 12 Jun 2026 16:40:59 +0200
Subject: [PATCH 8/8] tests

---
 clang/test/CodeGenCXX/dllexport-ctor-closure.cpp |  9 ++++++++-
 clang/test/CodeGenCXX/microsoft-abi-throw.cpp    | 13 ++++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/clang/test/CodeGenCXX/dllexport-ctor-closure.cpp 
b/clang/test/CodeGenCXX/dllexport-ctor-closure.cpp
index 8aeb9b9176fcd..1b4940673f599 100644
--- a/clang/test/CodeGenCXX/dllexport-ctor-closure.cpp
+++ b/clang/test/CodeGenCXX/dllexport-ctor-closure.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple i686-windows-msvc -emit-llvm -std=c++14 \
+// RUN: %clang_cc1 -triple i686-windows-msvc -emit-llvm -std=c++20 \
 // RUN:    -fno-threadsafe-statics -fms-extensions -O1 -mconstructor-aliases \
 // RUN:    -disable-llvm-passes -o - %s -w -fms-compatibility-version=19.00 | \
 // RUN:    FileCheck %s
@@ -95,3 +95,10 @@ struct __declspec(dllexport) ConstexprDefaultArg {
   ConstexprDefaultArg(SomeStruct = kConstexprStruct) {}
 };
 // CHECK-LABEL: define weak_odr dso_local dllexport x86_thiscallcc void 
@"??_FConstexprDefaultArg@@QAEXXZ"
+
+consteval int constEvalFunc() { return 42; }
+struct ConstEvalDefaultArg {
+  __declspec(dllexport) ConstEvalDefaultArg(int n = constEvalFunc()) {}
+};
+// CHECK-LABEL: define weak_odr dso_local dllexport x86_thiscallcc void 
@"??_FConstEvalDefaultArg@@QAEXXZ"
+// CHECK: call {{.*}} @"??0ConstEvalDefaultArg@@QAE@H@Z"({{.*}}, i32 noundef 
42)
diff --git a/clang/test/CodeGenCXX/microsoft-abi-throw.cpp 
b/clang/test/CodeGenCXX/microsoft-abi-throw.cpp
index 14945ad60f3c1..4fd0df42d8ff5 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-throw.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-throw.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -emit-llvm -o - -triple=i386-pc-win32 -std=c++11 %s 
-fcxx-exceptions -fms-extensions | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -o - -triple=i386-pc-win32 -std=c++20 %s 
-fcxx-exceptions -fms-extensions | FileCheck %s
 
 // CHECK-DAG: @"??_R0?AUY@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { 
ptr @"??_7type_info@@6B@", ptr null, [8 x i8] c".?AUY@@\00" }, comdat
 // CHECK-DAG: @"_CT??_R0?AUY@@@8??0Y@@QAE@ABU0@@Z8" = linkonce_odr 
unnamed_addr constant %eh.CatchableType { i32 4, ptr @"??_R0?AUY@@@8", i32 0, 
i32 -1, i32 0, i32 8, ptr @"??0Y@@QAE@ABU0@@Z" }, section ".xdata", comdat
@@ -71,6 +71,17 @@ void h(Default &d) {
   throw d;
 }
 
+consteval int constEvalFunc() { return 123; }
+struct DefaultConstEval {
+  DefaultConstEval(DefaultConstEval&, int = constEvalFunc());
+};
+// CHECK-LABEL: @"??_ODefaultConstEval@@QAEXAAU0@@Z"
+// CHECK: call x86_thiscallcc {{.*}} 
@"??0DefaultConstEval@@QAE@AAU0@H@Z"({{.*}} %[[this]], {{.*}} %[[src]], i32 
noundef 123)
+
+void h2(DefaultConstEval &d) {
+  throw d;
+}
+
 struct DeletedCopy {
   DeletedCopy();
   DeletedCopy(DeletedCopy &&);

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