[MS] Fix constexpr data member pointer conversions

Constexpr data member conversions work by starting with the class that
originally introduced the field, and converting from there to the type
that the user desires. Before this change, Clang was using the
inheritance model from the final destination class type instead of the
model from the class that originally introduced the field. To fix this,
find the relevant FieldDecl and take its parent class instead of using
the member pointer type the user provided.

Indirect field decls require some special handling to find the parent
class.

Fixes PR43803

1 files changed, 18 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 2d8b538bc2e..7ec3950bc6f 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -619,6 +619,9 @@ private:
   llvm::Function *EmitVirtualMemPtrThunk(const CXXMethodDecl *MD,
                                          const MethodVFTableLocation &ML);
 
+  llvm::Constant *EmitMemberDataPointer(const CXXRecordDecl *RD,
+                                        CharUnits offset);
+
 public:
   llvm::Type *ConvertMemberPointerType(const MemberPointerType *MPT) override;
 
@@ -2702,7 +2705,11 @@ MicrosoftCXXABI::EmitFullMemberPointer(llvm::Constant *FirstField,
 llvm::Constant *
 MicrosoftCXXABI::EmitMemberDataPointer(const MemberPointerType *MPT,
                                        CharUnits offset) {
-  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
+  return EmitMemberDataPointer(MPT->getMostRecentCXXRecordDecl(), offset);
+}
+
+llvm::Constant *MicrosoftCXXABI::EmitMemberDataPointer(const CXXRecordDecl *RD,
+                                                       CharUnits offset) {
   if (RD->getMSInheritanceModel() ==
       MSInheritanceAttr::Keyword_virtual_inheritance)
     offset -= getContext().getOffsetOfBaseWithVBPtr(RD);
@@ -2726,8 +2733,17 @@ llvm::Constant *MicrosoftCXXABI::EmitMemberPointer(const APValue &MP,
   if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(MPD)) {
     C = EmitMemberFunctionPointer(MD);
   } else {
+    // For a pointer to data member, start off with the offset of the field in
+    // the class in which it was declared, and convert from there if necessary.
+    // For indirect field decls, get the outermost anonymous field and use the
+    // parent class.
     CharUnits FieldOffset = Ctx.toCharUnitsFromBits(Ctx.getFieldOffset(MPD));
-    C = EmitMemberDataPointer(DstTy, FieldOffset);
+    const FieldDecl *FD = dyn_cast<FieldDecl>(MPD);
+    if (!FD)
+      FD = cast<FieldDecl>(*cast<IndirectFieldDecl>(MPD)->chain_begin());
+    const CXXRecordDecl *RD = cast<CXXRecordDecl>(FD->getParent());
+    RD = RD->getMostRecentNonInjectedDecl();
+    C = EmitMemberDataPointer(RD, FieldOffset);
   }
 
   if (!MemberPointerPath.empty()) {