[clang] Ensure correct metadata for relative vtables

Prior to this, metadata pertaining to the size or address point offsets
into a relative vtable were twice the value they should be (treating
component widths as pointer width rather than 4 bytes). This prevented
some vtables from being devirtualized with D134320. This ensures the
correct metadata is written so whole program devirtualization can catch
these remaining devirt targets.

Differential Revision: https://reviews.llvm.org/D134687

1 files changed, 15 insertions, 8 deletions

diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index a9eb1a0..85acebe 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -678,15 +678,23 @@ void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
                                       /*position=*/vtableAddressPoint);
 }
 
-bool CodeGenVTables::useRelativeLayout() const {
+static bool UseRelativeLayout(const CodeGenModule &CGM) {
   return CGM.getTarget().getCXXABI().isItaniumFamily() &&
          CGM.getItaniumVTableContext().isRelativeLayout();
 }
 
+bool CodeGenVTables::useRelativeLayout() const {
+  return UseRelativeLayout(CGM);
+}
+
+llvm::Type *CodeGenModule::getVTableComponentType() const {
+  if (UseRelativeLayout(*this))
+    return Int32Ty;
+  return Int8PtrTy;
+}
+
 llvm::Type *CodeGenVTables::getVTableComponentType() const {
-  if (useRelativeLayout())
-    return CGM.Int32Ty;
-  return CGM.Int8PtrTy;
+  return CGM.getVTableComponentType();
 }
 
 static void AddPointerLayoutOffset(const CodeGenModule &CGM,
@@ -1281,8 +1289,7 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
   if (!getCodeGenOpts().LTOUnit)
     return;
 
-  CharUnits PointerWidth = Context.toCharUnitsFromBits(
-      Context.getTargetInfo().getPointerWidth(LangAS::Default));
+  CharUnits ComponentWidth = GetTargetTypeStoreSize(getVTableComponentType());
 
   typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
   std::vector<AddressPoint> AddressPoints;
@@ -1320,7 +1327,7 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
   ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
   for (auto AP : AddressPoints) {
     // Create type metadata for the address point.
-    AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
+    AddVTableTypeMetadata(VTable, ComponentWidth * AP.second, AP.first);
 
     // The class associated with each address point could also potentially be
     // used for indirect calls via a member function pointer, so we need to
@@ -1333,7 +1340,7 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
           Context.getMemberPointerType(
               Comps[I].getFunctionDecl()->getType(),
               Context.getRecordType(AP.first).getTypePtr()));
-      VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
+      VTable->addTypeMetadata((ComponentWidth * I).getQuantity(), MD);
     }
   }