commit 07ee46d613d7c1862878d7c7d1208a7b3e37459d
author Reid Kleckner <rnk@google.com> Mon Oct 28 17:05:34 2019 -0700
committer Reid Kleckner <rnk@google.com> Tue Oct 29 16:58:00 2019 -0700
tree 55142146f32a60aa83f81f7717ac074ef5e3bb81
parent 44bac3ed5291031174ff62a2e841210ff8aedb66

[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

clang/lib/CodeGen/MicrosoftCXXABI.cpp

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 2d8b538..7ec3950 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -619,6 +619,9 @@
   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 @@
 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 @@
   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()) {

clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp

diff --git a/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp b/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp
index 51dd889..bfe620d 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-member-pointers.cpp
@@ -121,6 +121,33 @@
 }
 } // namespace pr37399
 
+namespace pr43803 {
+// This case is interesting because it exercises conversion between member
+// pointer types when emitting constants.
+
+struct B;
+struct C { int B::*option; };
+extern const C table[3];
+struct A {
+  int x, y;
+  // Test the indirect case.
+  struct {
+    int z;
+  };
+};
+struct B : A {};
+const C table[] = {
+    {&B::x},
+    {&B::y},
+    {&B::z},
+};
+
+// CHECK: @"?table@pr43803@@3QBUC@1@B" = dso_local constant [3 x %"struct.pr43803::C"]
+// CHECK-SAME: [%"struct.pr43803::C" { { i32, i32, i32 } zeroinitializer, [4 x i8] undef },
+// CHECK-SAME:  %"struct.pr43803::C" { { i32, i32, i32 } { i32 4, i32 0, i32 0 }, [4 x i8] undef },
+// CHECK-SAME:  %"struct.pr43803::C" { { i32, i32, i32 } { i32 8, i32 0, i32 0 }, [4 x i8] undef }]
+}
+
 struct PR26313_Y;
 typedef void (PR26313_Y::*PR26313_FUNC)();
 struct PR26313_X {