Revert "[clang] fix broken canonicalization of DeducedTemplateSpecializationType (llvm#95202)"

This reverts commit 2e1ad93.

Reverting llvm#95202 in the 19.x branch

Fixes llvm#106182

The change in llvm#95202 causes code to crash and there is
no good way to backport a fix for that as there are ABI-impacting
changes at play.
Instead we revert llvm#95202 in the 19x branch, fixing the regression
and preserving the 18.x behavior (which is GCC's behavior)

llvm#106335 (comment)

Author: cor3ntin

clang/include/clang/AST/ASTContext.h

@@ -1888,13 +1888,6 @@ class ASTContext : public RefCountedBase<ASTContext> {
                                                 QualType DeducedType,
                                                 bool IsDependent) const;
 
-private:
-  QualType getDeducedTemplateSpecializationTypeInternal(TemplateName Template,
-                                                        QualType DeducedType,
-                                                        bool IsDependent,
-                                                        QualType Canon) const;
-
-public:
   /// Return the unique reference to the type for the specified TagDecl
   /// (struct/union/class/enum) decl.
   QualType getTagDeclType(const TagDecl *Decl) const;

clang/include/clang/AST/TemplateName.h

@@ -380,9 +380,7 @@ class TemplateName {
   /// error.
   void dump() const;
 
-  void Profile(llvm::FoldingSetNodeID &ID) {
-    ID.AddPointer(Storage.getOpaqueValue());
-  }
+  void Profile(llvm::FoldingSetNodeID &ID);
 
   /// Retrieve the template name as a void pointer.
   void *getAsVoidPointer() const { return Storage.getOpaqueValue(); }

clang/include/clang/AST/Type.h

@@ -6615,27 +6615,30 @@ class DeducedTemplateSpecializationType : public DeducedType,
 
   DeducedTemplateSpecializationType(TemplateName Template,
                                     QualType DeducedAsType,
-                                    bool IsDeducedAsDependent, QualType Canon)
+                                    bool IsDeducedAsDependent)
       : DeducedType(DeducedTemplateSpecialization, DeducedAsType,
                     toTypeDependence(Template.getDependence()) |
                         (IsDeducedAsDependent
                              ? TypeDependence::DependentInstantiation
                              : TypeDependence::None),
-                    Canon),
+                    DeducedAsType.isNull() ? QualType(this, 0)
+                                           : DeducedAsType.getCanonicalType()),
         Template(Template) {}
 
 public:
   /// Retrieve the name of the template that we are deducing.
   TemplateName getTemplateName() const { return Template;}
 
-  void Profile(llvm::FoldingSetNodeID &ID) const {
+  void Profile(llvm::FoldingSetNodeID &ID) {
     Profile(ID, getTemplateName(), getDeducedType(), isDependentType());
   }
 
   static void Profile(llvm::FoldingSetNodeID &ID, TemplateName Template,
                       QualType Deduced, bool IsDependent) {
     Template.Profile(ID);
-    Deduced.Profile(ID);
+    QualType CanonicalType =
+        Deduced.isNull() ? Deduced : Deduced.getCanonicalType();
+    ID.AddPointer(CanonicalType.getAsOpaquePtr());
     ID.AddBoolean(IsDependent || Template.isDependent());
   }
 

clang/lib/AST/ASTContext.cpp

@@ -6509,9 +6509,11 @@ QualType ASTContext::getUnconstrainedType(QualType T) const {
   return T;
 }
 
-QualType ASTContext::getDeducedTemplateSpecializationTypeInternal(
-    TemplateName Template, QualType DeducedType, bool IsDependent,
-    QualType Canon) const {
+/// Return the uniqued reference to the deduced template specialization type
+/// which has been deduced to the given type, or to the canonical undeduced
+/// such type, or the canonical deduced-but-dependent such type.
+QualType ASTContext::getDeducedTemplateSpecializationType(
+    TemplateName Template, QualType DeducedType, bool IsDependent) const {
   // Look in the folding set for an existing type.
   void *InsertPos = nullptr;
   llvm::FoldingSetNodeID ID;
@@ -6522,8 +6524,7 @@ QualType ASTContext::getDeducedTemplateSpecializationTypeInternal(
     return QualType(DTST, 0);
 
   auto *DTST = new (*this, alignof(DeducedTemplateSpecializationType))
-      DeducedTemplateSpecializationType(Template, DeducedType, IsDependent,
-                                        Canon);
+      DeducedTemplateSpecializationType(Template, DeducedType, IsDependent);
   llvm::FoldingSetNodeID TempID;
   DTST->Profile(TempID);
   assert(ID == TempID && "ID does not match");
@@ -6532,20 +6533,6 @@ QualType ASTContext::getDeducedTemplateSpecializationTypeInternal(
   return QualType(DTST, 0);
 }
 
-/// Return the uniqued reference to the deduced template specialization type
-/// which has been deduced to the given type, or to the canonical undeduced
-/// such type, or the canonical deduced-but-dependent such type.
-QualType ASTContext::getDeducedTemplateSpecializationType(
-    TemplateName Template, QualType DeducedType, bool IsDependent) const {
-  QualType Canon = DeducedType.isNull()
-                       ? getDeducedTemplateSpecializationTypeInternal(
-                             getCanonicalTemplateName(Template), QualType(),
-                             IsDependent, QualType())
-                       : DeducedType.getCanonicalType();
-  return getDeducedTemplateSpecializationTypeInternal(Template, DeducedType,
-                                                      IsDependent, Canon);
-}
-
 /// getAtomicType - Return the uniqued reference to the atomic type for
 /// the given value type.
 QualType ASTContext::getAtomicType(QualType T) const {

clang/lib/AST/TemplateName.cpp

@@ -350,6 +350,15 @@ bool TemplateName::containsUnexpandedParameterPack() const {
   return getDependence() & TemplateNameDependence::UnexpandedPack;
 }
 
+void TemplateName::Profile(llvm::FoldingSetNodeID &ID) {
+  if (const auto* USD = getAsUsingShadowDecl())
+    ID.AddPointer(USD->getCanonicalDecl());
+  else if (const auto *TD = getAsTemplateDecl())
+    ID.AddPointer(TD->getCanonicalDecl());
+  else
+    ID.AddPointer(Storage.getOpaqueValue());
+}
+
 void TemplateName::print(raw_ostream &OS, const PrintingPolicy &Policy,
                          Qualified Qual) const {
   auto handleAnonymousTTP = [](TemplateDecl *TD, raw_ostream &OS) {

clang/unittests/AST/CMakeLists.txt

@@ -32,7 +32,6 @@ add_clang_unittest(ASTTests
   EvaluateAsRValueTest.cpp
   ExternalASTSourceTest.cpp
   NamedDeclPrinterTest.cpp
-  ProfilingTest.cpp
   RandstructTest.cpp
   RawCommentForDeclTest.cpp
   RecursiveASTVisitorTest.cpp