Revert "[CodeGen] Add initial support for union members in TBAA"

This reverts commit r319413. See PR35503.

We can't use "union member" as the access type here like this.

llvm-svn: 319629

Author: Hal Finkel

clang/lib/CodeGen/CGExpr.cpp

@@ -3723,6 +3723,9 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
   if (base.getTBAAInfo().isMayAlias() ||
           rec->hasAttr<MayAliasAttr>() || FieldType->isVectorType()) {
     FieldTBAAInfo = TBAAAccessInfo::getMayAliasInfo();
+  } else if (rec->isUnion()) {
+    // TODO: Support TBAA for unions.
+    FieldTBAAInfo = TBAAAccessInfo::getMayAliasInfo();
   } else {
     // If no base type been assigned for the base access, then try to generate
     // one for this base lvalue.
@@ -3733,26 +3736,16 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
                "Nonzero offset for an access with no base type!");
     }
 
-    // All union members are encoded to be of the same special type.
-    if (FieldTBAAInfo.BaseType && rec->isUnion())
-      FieldTBAAInfo = TBAAAccessInfo::getUnionMemberInfo(FieldTBAAInfo.BaseType,
-                                                         FieldTBAAInfo.Offset,
-                                                         FieldTBAAInfo.Size);
-
-    // For now we describe accesses to direct and indirect union members as if
-    // they were at the offset of their outermost enclosing union.
-    if (!FieldTBAAInfo.isUnionMember()) {
-      // Adjust offset to be relative to the base type.
-      const ASTRecordLayout &Layout =
-          getContext().getASTRecordLayout(field->getParent());
-      unsigned CharWidth = getContext().getCharWidth();
-      if (FieldTBAAInfo.BaseType)
-        FieldTBAAInfo.Offset +=
-            Layout.getFieldOffset(field->getFieldIndex()) / CharWidth;
-
-      // Update the final access type.
-      FieldTBAAInfo.AccessType = CGM.getTBAATypeInfo(FieldType);
-    }
+    // Adjust offset to be relative to the base type.
+    const ASTRecordLayout &Layout =
+        getContext().getASTRecordLayout(field->getParent());
+    unsigned CharWidth = getContext().getCharWidth();
+    if (FieldTBAAInfo.BaseType)
+      FieldTBAAInfo.Offset +=
+          Layout.getFieldOffset(field->getFieldIndex()) / CharWidth;
+
+    // Update the final access type.
+    FieldTBAAInfo.AccessType = CGM.getTBAATypeInfo(FieldType);
   }
 
   Address addr = base.getAddress();

clang/lib/CodeGen/CodeGenModule.h

@@ -688,9 +688,8 @@ class CodeGenModule : public CodeGenTypeCache {
   /// getTBAAInfoForSubobject - Get TBAA information for an access with a given
   /// base lvalue.
   TBAAAccessInfo getTBAAInfoForSubobject(LValue Base, QualType AccessType) {
-    TBAAAccessInfo TBAAInfo = Base.getTBAAInfo();
-    if (TBAAInfo.isMayAlias() || TBAAInfo.isUnionMember())
-      return TBAAInfo;
+    if (Base.getTBAAInfo().isMayAlias())
+      return TBAAAccessInfo::getMayAliasInfo();
     return getTBAAAccessInfo(AccessType);
   }
 

clang/lib/CodeGen/CodeGenTBAA.cpp

@@ -74,10 +74,6 @@ llvm::MDNode *CodeGenTBAA::getChar() {
   return Char;
 }
 
-llvm::MDNode *CodeGenTBAA::getUnionMemberType(uint64_t Size) {
-  return createScalarTypeNode("union member", getChar(), Size);
-}
-
 static bool TypeHasMayAlias(QualType QTy) {
   // Tagged types have declarations, and therefore may have attributes.
   if (const TagType *TTy = dyn_cast<TagType>(QTy))
@@ -105,8 +101,9 @@ static bool isValidBaseType(QualType QTy) {
       return false;
     if (RD->hasFlexibleArrayMember())
       return false;
-    // For now, we do not allow interface classes to be base access types.
-    if (RD->isStruct() || RD->isClass() || RD->isUnion())
+    // RD can be struct, union, class, interface or enum.
+    // For now, we only handle struct and class.
+    if (RD->isStruct() || RD->isClass())
       return true;
   }
   return false;
@@ -280,27 +277,18 @@ llvm::MDNode *CodeGenTBAA::getBaseTypeInfoHelper(const Type *Ty) {
     const RecordDecl *RD = TTy->getDecl()->getDefinition();
     const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
     SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
-    if (RD->isUnion()) {
-      // Unions are represented as structures with a single member that has a
-      // special type and occupies the whole object.
-      uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity();
-      llvm::MDNode *TypeNode = getUnionMemberType(Size);
-      Fields.push_back(llvm::MDBuilder::TBAAStructField(/* Offset= */ 0, Size,
+    for (FieldDecl *Field : RD->fields()) {
+      QualType FieldQTy = Field->getType();
+      llvm::MDNode *TypeNode = isValidBaseType(FieldQTy) ?
+          getBaseTypeInfo(FieldQTy) : getTypeInfo(FieldQTy);
+      if (!TypeNode)
+        return BaseTypeMetadataCache[Ty] = nullptr;
+
+      uint64_t BitOffset = Layout.getFieldOffset(Field->getFieldIndex());
+      uint64_t Offset = Context.toCharUnitsFromBits(BitOffset).getQuantity();
+      uint64_t Size = Context.getTypeSizeInChars(FieldQTy).getQuantity();
+      Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size,
                                                         TypeNode));
-    } else {
-      for (FieldDecl *Field : RD->fields()) {
-        QualType FieldQTy = Field->getType();
-        llvm::MDNode *TypeNode = isValidBaseType(FieldQTy) ?
-            getBaseTypeInfo(FieldQTy) : getTypeInfo(FieldQTy);
-        if (!TypeNode)
-          return nullptr;
-
-        uint64_t BitOffset = Layout.getFieldOffset(Field->getFieldIndex());
-        uint64_t Offset = Context.toCharUnitsFromBits(BitOffset).getQuantity();
-        uint64_t Size = Context.getTypeSizeInChars(FieldQTy).getQuantity();
-        Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size,
-                                                          TypeNode));
-      }
     }
 
     SmallString<256> OutName;
@@ -345,8 +333,6 @@ llvm::MDNode *CodeGenTBAA::getAccessTagInfo(TBAAAccessInfo Info) {
 
   if (Info.isMayAlias())
     Info = TBAAAccessInfo(getChar(), Info.Size);
-  else if (Info.isUnionMember())
-    Info.AccessType = getUnionMemberType(Info.Size);
 
   if (!Info.AccessType)
     return nullptr;

clang/lib/CodeGen/CodeGenTBAA.h

@@ -34,10 +34,9 @@ class CGRecordLayout;
 
 // TBAAAccessKind - A kind of TBAA memory access descriptor.
 enum class TBAAAccessKind : unsigned {
-  Ordinary,     // An ordinary memory access.
-  MayAlias,     // An access that may alias with any other accesses.
-  Incomplete,   // Used to designate pointee values of incomplete types.
-  UnionMember,  // An access to a direct or indirect union member.
+  Ordinary,
+  MayAlias,
+  Incomplete,
 };
 
 // TBAAAccessInfo - Describes a memory access in terms of TBAA.
@@ -78,14 +77,6 @@ struct TBAAAccessInfo {
 
   bool isIncomplete() const { return Kind == TBAAAccessKind::Incomplete; }
 
-  static TBAAAccessInfo getUnionMemberInfo(llvm::MDNode *BaseType,
-                                           uint64_t Offset, uint64_t Size) {
-    return TBAAAccessInfo(TBAAAccessKind::UnionMember, BaseType,
-                          /* AccessType= */ nullptr, Offset, Size);
-  }
-
-  bool isUnionMember() const { return Kind == TBAAAccessKind::UnionMember; }
-
   bool operator==(const TBAAAccessInfo &Other) const {
     return Kind == Other.Kind &&
            BaseType == Other.BaseType &&
@@ -157,10 +148,6 @@ class CodeGenTBAA {
   /// considered to be equivalent to it.
   llvm::MDNode *getChar();
 
-  /// getUnionMemberType - Get metadata that represents the type of union
-  /// members.
-  llvm::MDNode *getUnionMemberType(uint64_t Size);
-
   /// CollectFields - Collect information about the fields of a type for
   /// !tbaa.struct metadata formation. Return false for an unsupported type.
   bool CollectFields(uint64_t BaseOffset,

clang/test/CodeGen/tbaa-union.cpp

@@ -15,32 +15,30 @@ void fred(unsigned Num, int Vec[2], int *Index, int Arr[4][2]) {
 // But no tbaa for the two stores:
 // CHECK: %uw[[UW1:[0-9]*]] = getelementptr
 // CHECK: store{{.*}}%uw[[UW1]]
-// CHECK: tbaa [[TAG_vect32_union_member:![0-9]+]]
+// CHECK: tbaa ![[OCPATH:[0-9]+]]
 // There will be a load after the store, and it will use tbaa. Make sure
 // the check-not above doesn't find it:
 // CHECK: load
   Tmp[*Index][0].uw = Arr[*Index][0] * Num;
 // CHECK: %uw[[UW2:[0-9]*]] = getelementptr
 // CHECK: store{{.*}}%uw[[UW2]]
-// CHECK: tbaa [[TAG_vect32_union_member]]
+// CHECK: tbaa ![[OCPATH]]
   Tmp[*Index][1].uw = Arr[*Index][1] * Num;
 // Same here, don't generate tbaa for the loads:
 // CHECK: %uh[[UH1:[0-9]*]] = bitcast %union.vect32
 // CHECK: %arrayidx[[AX1:[0-9]*]] = getelementptr{{.*}}%uh[[UH1]]
 // CHECK: load i16, i16* %arrayidx[[AX1]]
-// CHECK: tbaa [[TAG_vect32_union_member]]
+// CHECK: tbaa ![[OCPATH]]
 // CHECK: store
   Vec[0] = Tmp[*Index][0].uh[1];
 // CHECK: %uh[[UH2:[0-9]*]] = bitcast %union.vect32
 // CHECK: %arrayidx[[AX2:[0-9]*]] = getelementptr{{.*}}%uh[[UH2]]
 // CHECK: load i16, i16* %arrayidx[[AX2]]
-// CHECK: tbaa [[TAG_vect32_union_member]]
+// CHECK: tbaa ![[OCPATH]]
 // CHECK: store
   Vec[1] = Tmp[*Index][1].uh[1];
   bar(Tmp);
 }
 
-// CHECK-DAG: [[TAG_vect32_union_member]] = !{[[TYPE_vect32:!.*]], [[TYPE_union_member:!.*]], i64 0}
-// CHECK-DAG: [[TYPE_vect32]] = !{!"", [[TYPE_union_member]], i64 0}
-// CHECK-DAG: [[TYPE_union_member]] = !{!"union member", [[TYPE_char:!.*]], i64 0}
-// CHECK-DAG: [[TYPE_char]] = !{!"omnipotent char", {{.*}}}
+// CHECK-DAG: ![[CHAR:[0-9]+]] = !{!"omnipotent char"
+// CHECK-DAG: ![[OCPATH]] = !{![[CHAR]], ![[CHAR]], i64 0}