[clang] [clang-tools-extra] [lldb] [clang] implement CWG1980 and CWG2064: instantiation-dependency improvements (PR #190495)

[Oliver Hunt via cfe-commits]

================
@@ -6691,34 +6745,35 @@ QualType ASTContext::getReferenceQualifiedType(const Expr *E) const {
 /// nodes. This would never be helpful, since each such type has its own
 /// expression, and would not give a significant memory saving, since there
 /// is an Expr tree under each such type.
-QualType ASTContext::getDecltypeType(Expr *E, QualType UnderlyingType) const {
-  // C++11 [temp.type]p2:
-  //   If an expression e involves a template parameter, decltype(e) denotes a
-  //   unique dependent type. Two such decltype-specifiers refer to the same
-  //   type only if their expressions are equivalent (14.5.6.1).
-  QualType CanonType;
-  if (!E->isInstantiationDependent()) {
-    CanonType = getCanonicalType(UnderlyingType);
-  } else if (!UnderlyingType.isNull()) {
-    CanonType = getDecltypeType(E, QualType());
-  } else {
-    llvm::FoldingSetNodeID ID;
-    DependentDecltypeType::Profile(ID, *this, E);
+QualType ASTContext::getDecltypeType(Expr *E,
+                                     CanonicalizationKindOrNone ExprCanonKind,
+                                     QualType UnderlyingType) const {
+  llvm::FoldingSetNodeID ID;
+  DecltypeType::Profile(ID, *this, E, ExprCanonKind, UnderlyingType);
 
-    void *InsertPos = nullptr;
-    if (DependentDecltypeType *Canon =
-            DependentDecltypeTypes.FindNodeOrInsertPos(ID, InsertPos))
-      return QualType(Canon, 0);
+  void *InsertPos = nullptr;
+  if (auto *T = DecltypeTypes.FindNodeOrInsertPos(ID, InsertPos))
+    return QualType(T, 0);
 
-    // Build a new, canonical decltype(expr) type.
-    auto *DT =
-        new (*this, alignof(DependentDecltypeType)) DependentDecltypeType(E);
-    DependentDecltypeTypes.InsertNode(DT, InsertPos);
-    Types.push_back(DT);
-    return QualType(DT, 0);
+  // C++26 [temp.type]p4: If an expression e is type-dependent, decltype(e)
+  // denotes a unique dependent type. Two such decltype-specifiers refer to the
+  // same type only if their expressions are equivalent ([temp.over.link]).
+  QualType CanonType;
+  if (!E->isTypeDependent()) {
----------------
ojhunt wrote:

nit: no braces

https://github.com/llvm/llvm-project/pull/190495