[CodeGen] Unify generation of scalar and struct-path TBAA tags

This patch makes it possible to produce access tags in a uniform
manner regardless whether the resulting tag will be a scalar or a
struct-path one. getAccessTagInfo() now takes care of the actual
translation of access descriptors to tags and can handle all
kinds of accesses. Facilities that specific to scalar accesses
are eliminated.

Some more details:
* DecorateInstructionWithTBAA() is not responsible for conversion
  of types to access tags anymore. Instead, it takes an access
  descriptor (TBAAAccessInfo) and generates corresponding access
  tag from it.
* getTBAAInfoForVTablePtr() reworked to
  getTBAAVTablePtrAccessInfo() that now returns the
  virtual-pointer access descriptor and not the virtual-point
  type metadata.
* Added function getTBAAMayAliasAccessInfo() that returns the
  descriptor for may-alias accesses.
* getTBAAStructTagInfo() renamed to getTBAAAccessTagInfo() as now
  it is the only way to generate access tag by a given access
  descriptor. It is capable of producing both scalar and
  struct-path tags, depending on options and availability of the
  base access type. getTBAAScalarTagInfo() and its cache
  ScalarTagMetadataCache are eliminated.
* Now that we do not need to care about whether the resulting
  access tag should be a scalar or struct-path one,
  getTBAAStructTypeInfo() is renamed to getBaseTypeInfo().
* Added function getTBAAAccessInfo() that constructs access
  descriptor by a given QualType access type.

This is part of D37826 reworked to be a separate patch to
simplify review.

Differential Revision: https://reviews.llvm.org/D38503

llvm-svn: 314977

1 files changed, 20 insertions, 18 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index a16f350f9d5..86153cc7d92 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -578,10 +578,14 @@ llvm::MDNode *CodeGenModule::getTBAATypeInfo(QualType QTy) {
   return TBAA->getTypeInfo(QTy);
 }
 
-llvm::MDNode *CodeGenModule::getTBAAInfoForVTablePtr() {
+TBAAAccessInfo CodeGenModule::getTBAAAccessInfo(QualType AccessType) {
+  return TBAAAccessInfo(getTBAATypeInfo(AccessType));
+}
+
+TBAAAccessInfo CodeGenModule::getTBAAVTablePtrAccessInfo() {
   if (!TBAA)
-    return nullptr;
-  return TBAA->getTBAAInfoForVTablePtr();
+    return TBAAAccessInfo();
+  return TBAA->getVTablePtrAccessInfo();
 }
 
 llvm::MDNode *CodeGenModule::getTBAAStructInfo(QualType QTy) {
@@ -590,30 +594,28 @@ llvm::MDNode *CodeGenModule::getTBAAStructInfo(QualType QTy) {
   return TBAA->getTBAAStructInfo(QTy);
 }
 
-llvm::MDNode *CodeGenModule::getTBAAStructTagInfo(TBAAAccessInfo Info) {
+llvm::MDNode *CodeGenModule::getTBAABaseTypeInfo(QualType QTy) {
   if (!TBAA)
     return nullptr;
-  return TBAA->getTBAAStructTagInfo(Info);
+  return TBAA->getBaseTypeInfo(QTy);
 }
 
-llvm::MDNode *CodeGenModule::getTBAAMayAliasTypeInfo() {
+llvm::MDNode *CodeGenModule::getTBAAAccessTagInfo(TBAAAccessInfo Info) {
   if (!TBAA)
     return nullptr;
-  return TBAA->getMayAliasTypeInfo();
+  return TBAA->getAccessTagInfo(Info);
+}
+
+TBAAAccessInfo CodeGenModule::getTBAAMayAliasAccessInfo() {
+  if (!TBAA)
+    return TBAAAccessInfo();
+  return TBAA->getMayAliasAccessInfo();
 }
 
-/// Decorate the instruction with a TBAA tag. For both scalar TBAA
-/// and struct-path aware TBAA, the tag has the same format:
-/// base type, access type and offset.
-/// When ConvertTypeToTag is true, we create a tag based on the scalar type.
 void CodeGenModule::DecorateInstructionWithTBAA(llvm::Instruction *Inst,
-                                                llvm::MDNode *TBAAInfo,
-                                                bool ConvertTypeToTag) {
-  if (ConvertTypeToTag && TBAA)
-    Inst->setMetadata(llvm::LLVMContext::MD_tbaa,
-                      TBAA->getTBAAScalarTagInfo(TBAAInfo));
-  else
-    Inst->setMetadata(llvm::LLVMContext::MD_tbaa, TBAAInfo);
+                                                TBAAAccessInfo TBAAInfo) {
+  if (llvm::MDNode *Tag = getTBAAAccessTagInfo(TBAAInfo))
+    Inst->setMetadata(llvm::LLVMContext::MD_tbaa, Tag);
 }
 
 void CodeGenModule::DecorateInstructionWithInvariantGroup(