[clang] AST: fix dependency calculation for TypedefTypes

[mizvekov]

The dependency from the type sugar of the underlying type of a Typedef were not being considered for the dependency of the TypedefType itself.

A TypedefType should be instantiation dependent if it involves non-instantiated template parameters, even if they don't contribute to the canonical type.

Besides, a TypedefType should be instantiation dependent if it is declared in a dependent context, but fixing that would have performance consequences, as otherwise non-dependent typedef declarations would need to be transformed during instantiation as well.

This removes the workaround added in #90032

Fixes #89774

[llvmbot]

@llvm/pr-subscribers-clang-codegen
@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-clang

Author: Matheus Izvekov (mizvekov)

Changes

The dependency from the type sugar of the underlying type of a Typedef were not being considered for the dependency of the TypedefType itself.

A TypedefType should be instantiation dependent if it involves non-instantiated template parameters, even if they don't contribute to the canonical type.

Besides, a TypedefType should be instantiation dependent if it is declared in a dependent context, but fixing that would have performance consequences, as otherwise non-dependent typedef declarations would need to be transformed during instantiation as well.

This removes the workaround added in #90032

Fixes #89774

---

Full diff: https://github.com/llvm/llvm-project/pull/143291.diff

6 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2-1)
• (modified) clang/include/clang/AST/Type.h (+2-2)
• (modified) clang/lib/AST/ASTContext.cpp (+2-2)
• (modified) clang/lib/AST/Type.cpp (+5-5)
• (modified) clang/lib/CodeGen/CGDebugInfo.cpp (+1-22)
• (modified) clang/test/CodeGenCXX/dependent-template-alias.cpp (+2-5)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1dd8b794c943a..322686fce0b04 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -687,7 +687,7 @@ Bug Fixes in This Version
 - Fixed an assertion failure in serialization of constexpr structs containing unions. (#GH140130)
 - Fixed duplicate entries in TableGen that caused the wrong attribute to be selected. (GH#140701)
 - Fixed type mismatch error when 'builtin-elementwise-math' arguments have different qualifiers, this should be well-formed. (#GH141397)
-- Constant evaluation now correctly runs the destructor of a variable declared in 
+- Constant evaluation now correctly runs the destructor of a variable declared in
   the second clause of a C-style ``for`` loop. (#GH139818)
 
 Bug Fixes to Compiler Builtins
@@ -843,6 +843,7 @@ Bug Fixes to AST Handling
 - Fixed uninitialized use check in a lambda within CXXOperatorCallExpr. (#GH129198)
 - Fixed a malformed printout of ``CXXParenListInitExpr`` in certain contexts.
 - Fixed a malformed printout of certain calling convention function attributes. (#GH143160)
+- Fixed dependency calculation for TypedefTypes (#GH89774)
 
 Miscellaneous Bug Fixes
 ^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
index a6c26a07800c3..040edd392b7aa 100644
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -5821,8 +5821,8 @@ class TypedefType final : public Type,
   friend class ASTContext; // ASTContext creates these.
   friend TrailingObjects;
 
-  TypedefType(TypeClass tc, const TypedefNameDecl *D, QualType underlying,
-              QualType can);
+  TypedefType(TypeClass tc, const TypedefNameDecl *D, QualType UnderlyingType,
+              bool HasTypeDifferentFromDecl);
 
 public:
   TypedefNameDecl *getDecl() const { return Decl; }
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 45f9602856840..b51f7622288df 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -5216,7 +5216,7 @@ QualType ASTContext::getTypedefType(const TypedefNameDecl *Decl,
     if (Underlying.isNull())
       Underlying = Decl->getUnderlyingType();
     auto *NewType = new (*this, alignof(TypedefType)) TypedefType(
-        Type::Typedef, Decl, QualType(), getCanonicalType(Underlying));
+        Type::Typedef, Decl, Underlying, /*HasTypeDifferentFromDecl=*/false);
     Decl->TypeForDecl = NewType;
     Types.push_back(NewType);
     return QualType(NewType, 0);
@@ -5238,7 +5238,7 @@ QualType ASTContext::getTypedefType(const TypedefNameDecl *Decl,
   void *Mem = Allocate(TypedefType::totalSizeToAlloc<QualType>(true),
                        alignof(TypedefType));
   auto *NewType = new (Mem) TypedefType(Type::Typedef, Decl, Underlying,
-                                        getCanonicalType(Underlying));
+                                        /*HasTypeDifferentFromDecl=*/true);
   TypedefTypes.InsertNode(NewType, InsertPos);
   Types.push_back(NewType);
   return QualType(NewType, 0);
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index 5bb39b12693fb..49f5e8138834b 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -4013,13 +4013,13 @@ StringRef CountAttributedType::getAttributeName(bool WithMacroPrefix) const {
 }
 
 TypedefType::TypedefType(TypeClass tc, const TypedefNameDecl *D,
-                         QualType Underlying, QualType can)
-    : Type(tc, can, toSemanticDependence(can->getDependence())),
+                         QualType UnderlyingType, bool HasTypeDifferentFromDecl)
+    : Type(tc, UnderlyingType.getCanonicalType(),
+           toSemanticDependence(UnderlyingType->getDependence())),
       Decl(const_cast<TypedefNameDecl *>(D)) {
-  assert(!isa<TypedefType>(can) && "Invalid canonical type");
-  TypedefBits.hasTypeDifferentFromDecl = !Underlying.isNull();
+  TypedefBits.hasTypeDifferentFromDecl = HasTypeDifferentFromDecl;
   if (!typeMatchesDecl())
-    *getTrailingObjects<QualType>() = Underlying;
+    *getTrailingObjects<QualType>() = UnderlyingType;
 }
 
 QualType TypedefType::desugar() const {
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 001b208e1c3ff..ee5e3d68a5ffa 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -1564,28 +1564,7 @@ llvm::DIType *CGDebugInfo::CreateType(const TemplateSpecializationType *Ty,
 
   SourceLocation Loc = AliasDecl->getLocation();
 
-  if (CGM.getCodeGenOpts().DebugTemplateAlias &&
-      // FIXME: This is a workaround for the issue
-      //        https://github.com/llvm/llvm-project/issues/89774
-      // The TemplateSpecializationType doesn't contain any instantiation
-      // information; dependent template arguments can't be resolved. For now,
-      // fall back to DW_TAG_typedefs for template aliases that are
-      // instantiation dependent, e.g.:
-      // ```
-      // template <int>
-      // using A = int;
-      //
-      // template<int I>
-      // struct S {
-      //   using AA = A<I>; // Instantiation dependent.
-      //   AA aa;
-      // };
-      //
-      // S<0> s;
-      // ```
-      // S::AA's underlying type A<I> is dependent on I so will be emitted as a
-      // DW_TAG_typedef.
-      !Ty->isInstantiationDependentType()) {
+  if (CGM.getCodeGenOpts().DebugTemplateAlias) {
     auto ArgVector = ::GetTemplateArgs(TD, Ty);
     TemplateArgs Args = {TD->getTemplateParameters(), ArgVector};
 
diff --git a/clang/test/CodeGenCXX/dependent-template-alias.cpp b/clang/test/CodeGenCXX/dependent-template-alias.cpp
index deb243f9fc88d..324b16f1919df 100644
--- a/clang/test/CodeGenCXX/dependent-template-alias.cpp
+++ b/clang/test/CodeGenCXX/dependent-template-alias.cpp
@@ -1,9 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-unk-unk -o - -emit-llvm -debug-info-kind=standalone -gtemplate-alias %s -gsimple-template-names=simple \
 // RUN: | FileCheck %s
 
-//// Check that -gtemplate-alias falls back to DW_TAG_typedef emission
-//// for instantiation dependent type aliases.
-
 template <int>
 using A = int;
 
@@ -16,6 +13,6 @@ struct S {
 S<0> s;
 
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "aa", scope: ![[#]], file: ![[#]], line: [[#]], baseType: ![[AA:[0-9]+]], size: 32)
-// CHECK: [[AA]] = !DIDerivedType(tag: DW_TAG_typedef, name: "AA", file: ![[#]], line: [[#]], baseType: ![[A:[0-9]+]])
-// CHECK: [[A]] = !DIDerivedType(tag: DW_TAG_typedef, name: "A<I>", file: ![[#]], line: [[#]], baseType: ![[int:[0-9]+]])
+// CHECK: [[AA]] = !DIDerivedType(tag: DW_TAG_typedef, name: "AA", scope: ![[#]], file: ![[#]], line: [[#]], baseType: ![[A:[0-9]+]])
+// CHECK: [[A]] = !DIDerivedType(tag: DW_TAG_template_alias, name: "A", file: ![[#]], line: [[#]], baseType: ![[int:[0-9]+]], extraData: ![[#]])
 // CHECK: [[int]] = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)

[zyn0217]

Thanks