[clang] [clang][NFC] Adjust TBAA Base Info API (PR #73263)

[Nathan Sidwell via cfe-commits]

https://github.com/urnathan created https://github.com/llvm/llvm-project/pull/73263

I noticed a couple of minor issues with CodeGenTBAA::getBaseTypeInfo.

1) isValidBaseType explicitly checks for a reference type to return false, but then also returns false for all non-record types. Just remove that reference check.

2) All uses of CodeGenTBAA::getBaseTypeInfo from within that class are when we've already checked the type isValidBaseType. The only case where this isn't true is from outside the class. It seems better to have two entry points in this case.  Adding a new
'maybeGetBaseTypeInfo' entry point for external uses that returns nullptr for non valid base types.  (Open to other names?)

[This is part one of a pair of changes.]

>From 2a312ddadae91ea52b184edaa0d19495c6e0f4a3 Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nathan at acm.org>
Date: Wed, 22 Nov 2023 20:45:38 -0500
Subject: [PATCH] [clang][NFC] Adjust TBAA Base Info API

I noticed a couple of minor issues with CodeGenTBAA::getBaseTypeInfo.

1) isValidBaseType explicitly checks for a reference type to return
false, but then also returns false for all non-record types. Just
remove that reference check.

2) All uses of CodeGenTBAA::getBaseTypeInfo from within that class are
when we've already checked the type isValidBaseType. The only case
where this isn't true is from outside the class. It seems better to
have two entry points in this case.  Adding a new
'maybeGetBaseTypeInfo' entry point for external uses that returns
nullptr for non valid base types.  (Open to other names?)

[This is part one of a pair of changes.]
---
 clang/lib/CodeGen/CodeGenModule.cpp |  2 +-
 clang/lib/CodeGen/CodeGenTBAA.cpp   |  9 +++++----
 clang/lib/CodeGen/CodeGenTBAA.h     | 11 ++++++++---
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 7cdf50a281cd278..e01fdc3579d88b8 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1318,7 +1318,7 @@ llvm::MDNode *CodeGenModule::getTBAAStructInfo(QualType QTy) {
 llvm::MDNode *CodeGenModule::getTBAABaseTypeInfo(QualType QTy) {
   if (!TBAA)
     return nullptr;
-  return TBAA->getBaseTypeInfo(QTy);
+  return TBAA->maybeGetBaseTypeInfo(QTy);
 }
 
 llvm::MDNode *CodeGenModule::getTBAAAccessTagInfo(TBAAAccessInfo Info) {
diff --git a/clang/lib/CodeGen/CodeGenTBAA.cpp b/clang/lib/CodeGen/CodeGenTBAA.cpp
index 8705d3d65f1a573..9b45a644937b8d9 100644
--- a/clang/lib/CodeGen/CodeGenTBAA.cpp
+++ b/clang/lib/CodeGen/CodeGenTBAA.cpp
@@ -95,8 +95,6 @@ static bool TypeHasMayAlias(QualType QTy) {
 
 /// Check if the given type is a valid base type to be used in access tags.
 static bool isValidBaseType(QualType QTy) {
-  if (QTy->isReferenceType())
-    return false;
   if (const RecordType *TTy = QTy->getAs<RecordType>()) {
     const RecordDecl *RD = TTy->getDecl()->getDefinition();
     // Incomplete types are not valid base access types.
@@ -414,8 +412,7 @@ llvm::MDNode *CodeGenTBAA::getBaseTypeInfoHelper(const Type *Ty) {
 }
 
 llvm::MDNode *CodeGenTBAA::getBaseTypeInfo(QualType QTy) {
-  if (!isValidBaseType(QTy))
-    return nullptr;
+  assert(isValidBaseType(QTy) && "Must be a valid base type");
 
   const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
   if (llvm::MDNode *N = BaseTypeMetadataCache[Ty])
@@ -428,6 +425,10 @@ llvm::MDNode *CodeGenTBAA::getBaseTypeInfo(QualType QTy) {
   return BaseTypeMetadataCache[Ty] = TypeNode;
 }
 
+llvm::MDNode *CodeGenTBAA::maybeGetBaseTypeInfo(QualType QTy) {
+  return isValidBaseType(QTy) ? getBaseTypeInfo(QTy) : nullptr;
+}
+
 llvm::MDNode *CodeGenTBAA::getAccessTagInfo(TBAAAccessInfo Info) {
   assert(!Info.isIncomplete() && "Access to an object of an incomplete type!");
 
diff --git a/clang/lib/CodeGen/CodeGenTBAA.h b/clang/lib/CodeGen/CodeGenTBAA.h
index a65963596fe9def..53d77e1fefc4352 100644
--- a/clang/lib/CodeGen/CodeGenTBAA.h
+++ b/clang/lib/CodeGen/CodeGenTBAA.h
@@ -166,6 +166,10 @@ class CodeGenTBAA {
   /// used to describe accesses to objects of the given base type.
   llvm::MDNode *getBaseTypeInfoHelper(const Type *Ty);
 
+  /// getBaseTypeInfo - Return metadata that describes the given base access
+  /// type. The type must be suitable.
+  llvm::MDNode *getBaseTypeInfo(QualType QTy);
+
 public:
   CodeGenTBAA(ASTContext &Ctx, llvm::Module &M, const CodeGenOptions &CGO,
               const LangOptions &Features, MangleContext &MContext);
@@ -187,9 +191,10 @@ class CodeGenTBAA {
   /// the given type.
   llvm::MDNode *getTBAAStructInfo(QualType QTy);
 
-  /// getBaseTypeInfo - Get metadata that describes the given base access type.
-  /// Return null if the type is not suitable for use in TBAA access tags.
-  llvm::MDNode *getBaseTypeInfo(QualType QTy);
+  /// maybeGetBaseTypeInfo - Get metadata that describes the given base access
+  /// type. Return null if the type is not suitable for use in TBAA access
+  /// tags.
+  llvm::MDNode *maybeGetBaseTypeInfo(QualType QTy);
 
   /// getAccessTagInfo - Get TBAA tag for a given memory access.
   llvm::MDNode *getAccessTagInfo(TBAAAccessInfo Info);