Rewrite parts of MS ABI C++ layout. Based on work by r4start; I ended up doing this while I was trying to review his patch.

llvm-svn: 142325

1 files changed, 82 insertions, 87 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index bbd3fc01601..86f4107e688 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -669,7 +669,7 @@ protected:
 
   void SelectPrimaryVBase(const CXXRecordDecl *RD);
 
-  CharUnits GetVirtualPointersSize(const CXXRecordDecl *RD) const;
+  void EnsureVTablePointerAlignment();
 
   /// LayoutNonVirtualBases - Determines the primary base class (if any) and
   /// lays it out. Will then proceed to lay out all non-virtual base clasess.
@@ -681,6 +681,9 @@ protected:
   void AddPrimaryVirtualBaseOffsets(const BaseSubobjectInfo *Info,
                                     CharUnits Offset);
 
+  bool HasNewVirtualFunction(const CXXRecordDecl *RD) const;
+  bool BaseHasVFPtr(const CXXRecordDecl *RD) const;
+
   /// LayoutVirtualBases - Lays out all the virtual bases.
   void LayoutVirtualBases(const CXXRecordDecl *RD,
                           const CXXRecordDecl *MostDerivedClass);
@@ -730,12 +733,6 @@ protected:
   void setDataSize(CharUnits NewSize) { DataSize = Context.toBits(NewSize); }
   void setDataSize(uint64_t NewSize) { DataSize = NewSize; }
 
-  bool HasVBPtr(const CXXRecordDecl *RD) const;
-  bool HasNewVirtualFunction(const CXXRecordDecl *RD) const;
-
-  /// Add vbptr or vfptr to layout.
-  void AddVPointer();
-
   RecordLayoutBuilder(const RecordLayoutBuilder&);   // DO NOT IMPLEMENT
   void operator=(const RecordLayoutBuilder&); // DO NOT IMPLEMENT
 public:
@@ -778,11 +775,6 @@ RecordLayoutBuilder::SelectPrimaryVBase(const CXXRecordDecl *RD) {
   }
 }
 
-CharUnits
-RecordLayoutBuilder::GetVirtualPointersSize(const CXXRecordDecl *RD) const {
-  return Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
-}
-
 /// DeterminePrimaryBase - Determine the primary base of the given class.
 void RecordLayoutBuilder::DeterminePrimaryBase(const CXXRecordDecl *RD) {
   // If the class isn't dynamic, it won't have a primary base.
@@ -813,44 +805,30 @@ void RecordLayoutBuilder::DeterminePrimaryBase(const CXXRecordDecl *RD) {
     }
   }
 
-  // Otherwise, it is the first nearly empty virtual base that is not an
-  // indirect primary virtual base class, if one exists.
+  // The Microsoft ABI doesn't have primary virtual bases.
+  if (Context.getTargetInfo().getCXXABI() == CXXABI_Microsoft) {
+    assert(!PrimaryBase && "Should not get here with a primary base!");
+    return;
+  }
+
+  // Under the Itanium ABI, if there is no non-virtual primary base class,
+  // try to compute the primary virtual base.  The primary virtual base is
+  // the first nearly empty virtual base that is not an indirect primary
+  // virtual base class, if one exists.
   if (RD->getNumVBases() != 0) {
     SelectPrimaryVBase(RD);
     if (PrimaryBase)
       return;
   }
 
-  // Otherwise, it is the first nearly empty virtual base that is not an
-  // indirect primary virtual base class, if one exists.
+  // Otherwise, it is the first indirect primary base class, if one exists.
   if (FirstNearlyEmptyVBase) {
     PrimaryBase = FirstNearlyEmptyVBase;
     PrimaryBaseIsVirtual = true;
     return;
   }
 
-  // Otherwise there is no primary base class.
   assert(!PrimaryBase && "Should not get here with a primary base!");
-
-  // Allocate the virtual table pointer at offset zero.
-  assert(DataSize == 0 && "Vtable pointer must be at offset zero!");
-
-  // Update the size.
-  setSize(getSize() + GetVirtualPointersSize(RD));
-  setDataSize(getSize());
-
-  CharUnits UnpackedBaseAlign = 
-    Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
-  CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
-
-  // The maximum field alignment overrides base align.
-  if (!MaxFieldAlignment.isZero()) {
-    BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
-    UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
-  }
-
-  // Update the alignment.
-  UpdateAlignment(BaseAlign, UnpackedBaseAlign);
 }
 
 BaseSubobjectInfo *
@@ -959,6 +937,25 @@ void RecordLayoutBuilder::ComputeBaseSubobjectInfo(const CXXRecordDecl *RD) {
 }
 
 void
+RecordLayoutBuilder::EnsureVTablePointerAlignment() {
+  CharUnits UnpackedBaseAlign = 
+    Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
+  CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
+
+  // The maximum field alignment overrides base align.
+  if (!MaxFieldAlignment.isZero()) {
+    BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
+    UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
+  }
+
+  // Round up the current record size to pointer alignment.
+  setDataSize(getDataSize().RoundUpToAlignment(BaseAlign));
+
+  // Update the alignment.
+  UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+}
+
+void
 RecordLayoutBuilder::LayoutNonVirtualBases(const CXXRecordDecl *RD) {
   // Then, determine the primary base class.
   DeterminePrimaryBase(RD);
@@ -992,6 +989,18 @@ RecordLayoutBuilder::LayoutNonVirtualBases(const CXXRecordDecl *RD) {
     }
   }
 
+  if (Context.getTargetInfo().getCXXABI() != CXXABI_Microsoft &&
+      !PrimaryBase && RD->isDynamicClass()) {
+    // Under the Itanium ABI, a dynamic class without a primary base has a
+    // vtable pointer.  It is placed at offset 0.
+    assert(DataSize == 0 && "Vtable pointer must be at offset zero!");
+    EnsureVTablePointerAlignment();
+    CharUnits PtrWidth = 
+      Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
+    setSize(getSize() + PtrWidth);
+    setDataSize(getSize());
+  }
+
   // Now lay out the non-virtual bases.
   for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
          E = RD->bases_end(); I != E; ++I) {
@@ -1013,6 +1022,30 @@ RecordLayoutBuilder::LayoutNonVirtualBases(const CXXRecordDecl *RD) {
 
     LayoutNonVirtualBase(BaseInfo);
   }
+
+  if (Context.getTargetInfo().getCXXABI() == CXXABI_Microsoft) {
+    // Under the MS ABI, there are separate virtual function table and
+    // virtual base table pointers. A vfptr is necessary a if a class defines
+    // a virtual function which is not overriding a function from a base;
+    // a vbptr is necessary if a class has virtual bases. Either can come
+    // from a primary base, if it exists.  Otherwise, they are placed
+    // after any base classes.
+    CharUnits PtrWidth = 
+      Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
+    if (HasNewVirtualFunction(RD) &&
+        (!PrimaryBase || !BaseHasVFPtr(PrimaryBase))) {
+      EnsureVTablePointerAlignment();
+      setSize(getSize() + PtrWidth);
+      setDataSize(getSize());
+    }
+    if (RD->getNumVBases() &&
+        (!PrimaryBase || !PrimaryBase->getNumVBases())) {
+      EnsureVTablePointerAlignment();
+      VBPtrOffset = getSize();
+      setSize(getSize() + PtrWidth);
+      setDataSize(getSize());
+    }
+  }
 }
 
 void RecordLayoutBuilder::LayoutNonVirtualBase(const BaseSubobjectInfo *Base) {
@@ -1061,18 +1094,6 @@ RecordLayoutBuilder::AddPrimaryVirtualBaseOffsets(const BaseSubobjectInfo *Info,
   }
 }
 
-void RecordLayoutBuilder::AddVPointer() {
-  CharUnits PtrWidth = 
-    Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
-  setSize(getSize() + PtrWidth);
-  setDataSize(getSize());
-
-  if (Alignment > PtrWidth) {
-    setSize(getSize() + (Alignment - PtrWidth));
-    setDataSize(getSize());
-  }
-}
-
 bool 
 RecordLayoutBuilder::HasNewVirtualFunction(const CXXRecordDecl *RD) const {
   for (CXXRecordDecl::method_iterator method = RD->method_begin();
@@ -1086,18 +1107,15 @@ RecordLayoutBuilder::HasNewVirtualFunction(const CXXRecordDecl *RD) const {
   return false;
 }
 
-bool
-RecordLayoutBuilder::HasVBPtr(const CXXRecordDecl *RD) const {
-  if (!RD->getNumBases())
-    return false;
-
-  for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
-       E = RD->bases_end(); I != E; ++I) {
-    if (!I->isVirtual()) {
-      return false;
-    }
-  }
-  return true;
+bool 
+RecordLayoutBuilder::BaseHasVFPtr(const CXXRecordDecl *Base) const {
+  // FIXME: This function is inefficient.
+  if (HasNewVirtualFunction(Base))
+    return true;
+  const ASTRecordLayout &Layout = Context.getASTRecordLayout(Base);
+  if (const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase())
+    return BaseHasVFPtr(PrimaryBase);
+  return false;
 }
 
 void
@@ -1244,8 +1262,8 @@ void RecordLayoutBuilder::Layout(const RecordDecl *D) {
 
 void RecordLayoutBuilder::Layout(const CXXRecordDecl *RD) {
   if (Context.getTargetInfo().getCXXABI() == CXXABI_Microsoft) {
-    MSLayout(RD);
-    return ;
+    //MSLayout(RD);
+    //return ;
   }
 
   InitializeLayout(RD);
@@ -1753,32 +1771,9 @@ void RecordLayoutBuilder::MSLayoutVirtualBases(const CXXRecordDecl *RD) {
 
 void RecordLayoutBuilder::MSLayout(const CXXRecordDecl *RD) {
 
-  bool IsVBPtrAddedToLayout = false;
-
   InitializeLayout(RD);
 
-  if (HasVBPtr(RD)) {
-    // If all bases are virtual and the class declares a new virtual function,
-    // MSVC builds a vfptr.
-    if (HasNewVirtualFunction(RD)) {
-      AddVPointer();
-    }
-
-    VBPtrOffset = getSize();
-    AddVPointer();
-    IsVBPtrAddedToLayout = true;
-
-    ComputeBaseSubobjectInfo(RD);
-  } else {
-    LayoutNonVirtualBases(RD);
-  }
-
-  if (RD->getNumVBases() &&
-      !IsVBPtrAddedToLayout) {
-    // Add vbptr.
-    VBPtrOffset = getSize();
-    AddVPointer();
-  }
+  LayoutNonVirtualBases(RD);
 
   LayoutFields(RD);