Add basic support for adding !tbaa.struct metadata on llvm.memcpy calls for

struct assignment.

llvm-svn: 164853

clang/lib/CodeGen/CGExprAgg.cpp

@@ -1362,11 +1362,17 @@ void CodeGenFunction::EmitAggregateCopy(llvm::Value *DestPtr,
       }
     }
   }
+
+  // Determine the metadata to describe the position of any padding in this
+  // memcpy, as well as the TBAA tags for the members of the struct, in case
+  // the optimizer wishes to expand it in to scalar memory operations.
+  llvm::MDNode *TBAAStructTag = CGM.getTBAAStructInfo(Ty);
   
   Builder.CreateMemCpy(DestPtr, SrcPtr,
                        llvm::ConstantInt::get(IntPtrTy, 
                                               TypeInfo.first.getQuantity()),
-                       alignment.getQuantity(), isVolatile);
+                       alignment.getQuantity(), isVolatile,
+                       /*TBAATag=*/0, TBAAStructTag);
 }
 
 void CodeGenFunction::MaybeEmitStdInitializerListCleanup(llvm::Value *loc,

clang/lib/CodeGen/CodeGenModule.cpp

@@ -202,6 +202,12 @@ llvm::MDNode *CodeGenModule::getTBAAInfoForVTablePtr() {
   return TBAA->getTBAAInfoForVTablePtr();
 }
 
+llvm::MDNode *CodeGenModule::getTBAAStructInfo(QualType QTy) {
+  if (!TBAA)
+    return 0;
+  return TBAA->getTBAAStructInfo(QTy);
+}
+
 void CodeGenModule::DecorateInstruction(llvm::Instruction *Inst,
                                         llvm::MDNode *TBAAInfo) {
   Inst->setMetadata(llvm::LLVMContext::MD_tbaa, TBAAInfo);

clang/lib/CodeGen/CodeGenModule.h

@@ -461,6 +461,7 @@ public:
 
   llvm::MDNode *getTBAAInfo(QualType QTy);
   llvm::MDNode *getTBAAInfoForVTablePtr();
+  llvm::MDNode *getTBAAStructInfo(QualType QTy);
 
   bool isTypeConstant(QualType QTy, bool ExcludeCtorDtor);
 

clang/lib/CodeGen/CodeGenTBAA.cpp

@@ -17,6 +17,7 @@
 
 #include "CodeGenTBAA.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/RecordLayout.h"
 #include "clang/AST/Mangle.h"
 #include "clang/Frontend/CodeGenOptions.h"
 #include "llvm/LLVMContext.h"
@@ -167,3 +168,59 @@ CodeGenTBAA::getTBAAInfo(QualType QTy) {
 llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
   return MDHelper.createTBAANode("vtable pointer", getRoot());
 }
+
+bool
+CodeGenTBAA::CollectFields(uint64_t BaseOffset,
+                           QualType QTy,
+                           SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
+                             Fields,
+                           bool MayAlias) {
+  /* Things not handled yet include: C++ base classes, bitfields, */
+
+  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
+    const RecordDecl *RD = TTy->getDecl()->getDefinition();
+    if (RD->hasFlexibleArrayMember())
+      return false;
+
+    // TODO: Handle C++ base classes.
+    if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
+      if (Decl->bases_begin() != Decl->bases_end())
+        return false;
+
+    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
+
+    unsigned idx = 0;
+    for (RecordDecl::field_iterator i = RD->field_begin(),
+         e = RD->field_end(); i != e; ++i, ++idx) {
+      uint64_t Offset = BaseOffset +
+                        Layout.getFieldOffset(idx) / Context.getCharWidth();
+      QualType FieldQTy = i->getType();
+      if (!CollectFields(Offset, FieldQTy, Fields,
+                         MayAlias || TypeHasMayAlias(FieldQTy)))
+        return false;
+    }
+    return true;
+  }
+
+  /* Otherwise, treat whatever it is as a field. */
+  uint64_t Offset = BaseOffset;
+  uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
+  llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
+  Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAAInfo));
+  return true;
+}
+
+llvm::MDNode *
+CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
+  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
+
+  if (llvm::MDNode *N = StructMetadataCache[Ty])
+    return N;
+
+  SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
+  if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
+    return MDHelper.createTBAAStructNode(Fields);
+
+  // For now, handle any other kind of type conservatively.
+  return StructMetadataCache[Ty] = NULL;
+}

clang/lib/CodeGen/CodeGenTBAA.h

@@ -49,6 +49,10 @@ class CodeGenTBAA {
   /// MetadataCache - This maps clang::Types to llvm::MDNodes describing them.
   llvm::DenseMap<const Type *, llvm::MDNode *> MetadataCache;
 
+  /// StructMetadataCache - This maps clang::Types to llvm::MDNodes describing
+  /// them for struct assignments.
+  llvm::DenseMap<const Type *, llvm::MDNode *> StructMetadataCache;
+
   llvm::MDNode *Root;
   llvm::MDNode *Char;
 
@@ -60,6 +64,13 @@ class CodeGenTBAA {
   /// considered to be equivalent to it.
   llvm::MDNode *getChar();
 
+  /// 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,
+                     QualType Ty,
+                     SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &Fields,
+                     bool MayAlias);
+
 public:
   CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext &VMContext,
               const CodeGenOptions &CGO,
@@ -74,6 +85,10 @@ public:
   /// getTBAAInfoForVTablePtr - Get the TBAA MDNode to be used for a
   /// dereference of a vtable pointer.
   llvm::MDNode *getTBAAInfoForVTablePtr();
+
+  /// getTBAAStructInfo - Get the TBAAStruct MDNode to be used for a memcpy of
+  /// the given type.
+  llvm::MDNode *getTBAAStructInfo(QualType QTy);
 };
 
 }  // end namespace CodeGen

clang/test/CodeGen/tbaa-struct.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -emit-llvm -o - -O1 %s | FileCheck %s
+//
+// Check that we generate !tbaa.struct metadata for struct copies.
+struct A {
+  short s;
+  int i;
+  char c;
+  int j;
+};
+
+void copy(struct A *a, struct A *b) {
+  *a = *b;
+}
+
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %{{.*}}, i8* %{{.*}}, i64 16, i32 4, i1 false), !tbaa.struct [[TS:!.*]]
+// CHECK: [[TS]] = metadata !{i64 0, i64 2, metadata !{{.*}}, i64 4, i64 4, metadata !{{.*}}, i64 8, i64 1, metadata !{{.*}}, i64 12, i64 4, metadata !{{.*}}}