[clang] MicrosoftCXXABI: restore the RecordToCopyCtor table when loading AST (#53486)

- Includes a regression test for the issue

Author: glebov-andrey

clang/include/clang/AST/CXXRecordDeclDefinitionBits.def

@@ -249,6 +249,11 @@ FIELD(HasDeclaredCopyAssignmentWithConstParam, 1, MERGE_OR)
 /// base classes or fields have a no-return destructor
 FIELD(IsAnyDestructorNoReturn, 1, NO_MERGE)
 
+/// Microsoft CXX ABI specific:
+/// Whether the copy constructor is used by a `throw` expression.
+/// Used by ASTReader to restore the sidecar RecordToCopyCtor LUT.
+FIELD(HasCopyConstructorForExceptionObject, 1, MERGE_OR)
+
 /// Whether the record type is intangible (if any base classes or fields have
 /// type that is intangible). HLSL only.
 FIELD(IsHLSLIntangible, 1, NO_MERGE)

clang/include/clang/AST/DeclCXX.h

@@ -1558,6 +1558,14 @@ class CXXRecordDecl : public RecordDecl {
   /// a field or in base class.
   bool isHLSLIntangible() const { return data().IsHLSLIntangible; }
 
+  bool hasCopyConstructorForExceptionObject() const {
+    return data().HasCopyConstructorForExceptionObject;
+  }
+
+  void setHasCopyConstructorForExceptionObject() {
+    data().HasCopyConstructorForExceptionObject = true;
+  }
+
   /// If the class is a local class [class.local], returns
   /// the enclosing function declaration.
   const FunctionDecl *isLocalClass() const {

clang/lib/AST/DeclCXX.cpp

@@ -109,9 +109,10 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       ImplicitCopyAssignmentHasConstParam(true),
       HasDeclaredCopyConstructorWithConstParam(false),
       HasDeclaredCopyAssignmentWithConstParam(false),
-      IsAnyDestructorNoReturn(false), IsHLSLIntangible(false), IsLambda(false),
-      IsParsingBaseSpecifiers(false), ComputedVisibleConversions(false),
-      HasODRHash(false), Definition(D) {}
+      IsAnyDestructorNoReturn(false),
+      HasCopyConstructorForExceptionObject(false), IsHLSLIntangible(false),
+      IsLambda(false), IsParsingBaseSpecifiers(false),
+      ComputedVisibleConversions(false), HasODRHash(false), Definition(D) {}
 
 CXXBaseSpecifier *CXXRecordDecl::DefinitionData::getBasesSlowCase() const {
   return Bases.get(Definition->getASTContext().getExternalSource());

clang/lib/Sema/SemaExprCXX.cpp

@@ -1082,6 +1082,10 @@ bool Sema::CheckCXXThrowOperand(SourceLocation ThrowLoc,
       // friendship or any other means).
       Context.addCopyConstructorForExceptionObject(Subobject, CD);
 
+      // Store the bit in CXXRecordDecl so that ASTReader can restore this
+      // mapping later.
+      Subobject->setHasCopyConstructorForExceptionObject();
+
       // 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) {

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -2327,6 +2327,20 @@ void ASTDeclReader::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
   }
 
   VisitCXXMethodDecl(D);
+
+  // Microsoft CXX ABI specific:
+  // Restore the RecordToCopyCtor sidecar LUT entry so that `throw` expressions
+  // find the correct copy constructor for exceptions during codegen.
+  // There is no need to check the target info because the
+  // HasCopyConstructorForExceptionObject bit only gets set for the MS ABI.
+  if (D->isCopyConstructor()) {
+    // TODO What if this is not the same copy constructor which was chosen by
+    //      LookupCopyingConstructor() in SemaExprCXX? Is there a better way?
+    auto *R = cast<CXXRecordDecl>(D->getDeclContext());
+    if (R->hasCopyConstructorForExceptionObject()) {
+      Reader.getContext().addCopyConstructorForExceptionObject(R, D);
+    }
+  }
 }
 
 void ASTDeclReader::VisitCXXDestructorDecl(CXXDestructorDecl *D) {

clang/test/PCH/cxx-exception-copy-ctor-crash.cpp

@@ -0,0 +1,19 @@
+// REQUIRES: system-windows, target={{.*-windows-msvc}}
+// RUN: %clang_cc1 -x c++ -std=c++17 -fcxx-exceptions -fexceptions -triple=%ms_abi_triple -emit-pch -building-pch-with-obj -fmodules-codegen -o %t.pch %S/cxx-exception-copy-ctor-crash.h
+// RUN: %clang_cc1 -x c++ -std=c++17 -fcxx-exceptions -fexceptions -triple=%ms_abi_triple -include-pch %t.pch -emit-obj -building-pch-with-obj -fmodules-codegen -o %t.pch.obj
+// RUN: %clang_cc1 -x c++ -std=c++17 -fcxx-exceptions -fexceptions -triple=%ms_abi_triple -include-pch %t.pch -emit-obj -o %t.obj %s
+// RUN: lld-link -subsystem:console -out:%t.exe %t.pch.obj %t.obj libucrt.lib libvcruntime.lib libcmt.lib
+// RUN: %t.exe
+
+// Regression test for https://github.com/llvm/llvm-project/issues/53486
+
+int main() {
+  try {
+    throw Exception();
+  } catch (const Exception ex) { // catch by value to trigger copy constructor
+  }
+  if (ctor_count != dtor_count) {
+    return 1;
+  }
+  return 0;
+}

clang/test/PCH/cxx-exception-copy-ctor-crash.h

@@ -0,0 +1,14 @@
+// Header for PCH test cxx-exception-copy-ctor-crash.cpp
+
+inline int ctor_count = 0;
+inline int dtor_count = 0;
+
+struct Exception {
+  Exception() { ++ctor_count; }
+  ~Exception() { ++dtor_count; }
+  Exception(const Exception &) noexcept { ++ctor_count; }
+};
+
+inline void throw_exception() {
+  throw Exception();
+}