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llvm-project/clang/test/AST/ast-dump-template-decls.cpp
Matheus Izvekov 91cdd35008
[clang] Improve nested name specifier AST representation (#147835) 
This is a major change on how we represent nested name qualifications in
the AST.

* The nested name specifier itself and how it's stored is changed. The
prefixes for types are handled within the type hierarchy, which makes
canonicalization for them super cheap, no memory allocation required.
Also translating a type into nested name specifier form becomes a no-op.
An identifier is stored as a DependentNameType. The nested name
specifier gains a lightweight handle class, to be used instead of
passing around pointers, which is similar to what is implemented for
TemplateName. There is still one free bit available, and this handle can
be used within a PointerUnion and PointerIntPair, which should keep
bit-packing aficionados happy.
* The ElaboratedType node is removed, all type nodes in which it could
previously apply to can now store the elaborated keyword and name
qualifier, tail allocating when present.
* TagTypes can now point to the exact declaration found when producing
these, as opposed to the previous situation of there only existing one
TagType per entity. This increases the amount of type sugar retained,
and can have several applications, for example in tracking module
ownership, and other tools which care about source file origins, such as
IWYU. These TagTypes are lazily allocated, in order to limit the
increase in AST size.

This patch offers a great performance benefit.

It greatly improves compilation time for
[stdexec](https://github.com/NVIDIA/stdexec). For one datapoint, for
`test_on2.cpp` in that project, which is the slowest compiling test,
this patch improves `-c` compilation time by about 7.2%, with the
`-fsyntax-only` improvement being at ~12%.

This has great results on compile-time-tracker as well:

![image](https://github.com/user-attachments/assets/700dce98-2cab-4aa8-97d1-b038c0bee831)

This patch also further enables other optimziations in the future, and
will reduce the performance impact of template specialization resugaring
when that lands.

It has some other miscelaneous drive-by fixes.

About the review: Yes the patch is huge, sorry about that. Part of the
reason is that I started by the nested name specifier part, before the
ElaboratedType part, but that had a huge performance downside, as
ElaboratedType is a big performance hog. I didn't have the steam to go
back and change the patch after the fact.

There is also a lot of internal API changes, and it made sense to remove
ElaboratedType in one go, versus removing it from one type at a time, as
that would present much more churn to the users. Also, the nested name
specifier having a different API avoids missing changes related to how
prefixes work now, which could make existing code compile but not work.

How to review: The important changes are all in
`clang/include/clang/AST` and `clang/lib/AST`, with also important
changes in `clang/lib/Sema/TreeTransform.h`.

The rest and bulk of the changes are mostly consequences of the changes
in API.

PS: TagType::getDecl is renamed to `getOriginalDecl` in this patch, just
for easier to rebasing. I plan to rename it back after this lands.

Fixes #136624
Fixes https://github.com/llvm/llvm-project/issues/43179
Fixes https://github.com/llvm/llvm-project/issues/68670
Fixes https://github.com/llvm/llvm-project/issues/92757
2025-08-09 05:06:53 -03:00

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// Test without serialization:
// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-unknown -ast-dump %s \
// RUN: | FileCheck -strict-whitespace %s
//
// Test with serialization:
// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-unknown -emit-pch -o %t %s
// RUN: %clang_cc1 -x c++ -std=c++17 -triple x86_64-unknown-unknown -include-pch %t -ast-dump-all /dev/null \
// RUN: | sed -e "s/ <undeserialized declarations>//" -e "s/ imported//" \
// RUN: | FileCheck --strict-whitespace %s
template <typename Ty>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <{{.*}}:1, line:[[@LINE+2]]:10> col:6 a
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 referenced typename depth 0 index 0 Ty
void a(Ty);
template <typename... Ty>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:13> col:6 b
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:23> col:23 referenced typename depth 0 index 0 ... Ty
void b(Ty...);
template <typename Ty, typename Uy>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+3]]:14> col:6 c
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 referenced typename depth 0 index 0 Ty
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <col:24, col:33> col:33 referenced typename depth 0 index 1 Uy
void c(Ty, Uy);
template <>
void c<float, int>(float, int);
// CHECK: FunctionDecl 0x{{[^ ]*}} prev 0x{{[^ ]*}} <line:[[@LINE-2]]:1, line:[[@LINE-1]]:30> col:6 c 'void (float, int)'
// CHECK: TemplateArgument type 'float'
// CHECK: TemplateArgument type 'int'
template <typename Ty, template<typename> typename Uy>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+4]]:18> col:6 d
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 referenced typename depth 0 index 0 Ty
// CHECK-NEXT: TemplateTemplateParmDecl 0x{{[^ ]*}} <col:24, col:52> col:52 depth 0 index 1 Uy
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <col:33> col:41 typename depth 1 index 0
void d(Ty, Uy<Ty>);
template <class Ty>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:10> col:6 e
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:17> col:17 referenced class depth 0 index 0 Ty
void e(Ty);
template <int N>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:17> col:6 f
// CHECK-NEXT: NonTypeTemplateParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:15> col:15 referenced 'int' depth 0 index 0 N
void f(int i = N);
template <typename Ty = int>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+3]]:10> col:6 g
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:25> col:20 referenced typename depth 0 index 0 Ty
// CHECK-NEXT: TemplateArgument type 'int'
void g(Ty);
template <typename = void>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+3]]:8> col:6 h
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:22> col:20 typename depth 0 index 0
// CHECK-NEXT: TemplateArgument type 'void'
void h();
template <typename Ty>
// CHECK: ClassTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+3]]:11> col:8 R
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 typename depth 0 index 0 Ty
// CHECK: ClassTemplateSpecialization 0x{{[^ ]*}} 'R'
struct R {};
template <>
// CHECK: ClassTemplateSpecializationDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:16> col:8 struct R definition
// CHECK: TemplateArgument type 'int'
struct R<int> {};
template <typename Ty, class Uy>
// CHECK: ClassTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+3]]:11> col:8 S
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 typename depth 0 index 0 Ty
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <col:24, col:30> col:30 class depth 0 index 1 Uy
struct S {};
template <typename Ty>
// CHECK: ClassTemplatePartialSpecializationDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+4]]:20> col:8 struct S definition
// CHECK: TemplateArgument type 'type-parameter-0-0'
// CHECK: TemplateArgument type 'int'
// CHECK: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-4]]:11, col:20> col:20 referenced typename depth 0 index 0 Ty
struct S<Ty, int> {};
template <auto>
// CHECK: ClassTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:11> col:8 T
// CHECK-NEXT: NonTypeTemplateParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11> col:15 'auto' depth 0 index 0
struct T {};
template <decltype(auto)>
// CHECK: ClassTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:11> col:8 U
// CHECK-NEXT: NonTypeTemplateParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:24> col:25 'decltype(auto)' depth 0 index 0
struct U {};
template <typename Ty>
// CHECK: ClassTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+7]]:1> line:[[@LINE+2]]:8 V
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 typename depth 0 index 0 Ty
struct V {
template <typename Uy>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:3, line:[[@LINE+2]]:10> col:8 f
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:13, col:22> col:22 typename depth 1 index 0 Uy
void f();
};
template <typename Ty>
template <typename Uy>
// CHECK: FunctionTemplateDecl 0x{{[^ ]*}} parent 0x{{[^ ]*}} prev 0x{{[^ ]*}} <line:[[@LINE-1]]:1, line:[[@LINE+2]]:18> col:13 f
// CHECK-NEXT: TemplateTypeParmDecl 0x{{[^ ]*}} <line:[[@LINE-2]]:11, col:20> col:20 typename depth 1 index 0 Uy
void V<Ty>::f() {}
namespace PR55886 {
template <class T> struct C {
template <class U> using type1 = U(T);
};
using type2 = typename C<int>::type1<void>;
// CHECK: TypeAliasDecl 0x{{[^ ]*}} <line:[[@LINE-1]]:1, col:42> col:7 type2 'typename C<int>::type1<void>':'void (int)'
// CHECK-NEXT: TemplateSpecializationType 0x{{[^ ]*}} 'typename C<int>::type1<void>' sugar alias
// CHECK-NEXT: name: 'C<int>::type1':'PR55886::C<int>::type1' qualified
// CHECK-NEXT: NestedNameSpecifier TypeSpec 'C<int>':'PR55886::C<int>'
// CHECK-NEXT: TypeAliasTemplateDecl {{.+}} type1
// CHECK-NEXT: TemplateArgument type 'void'
// CHECK-NEXT: BuiltinType 0x{{[^ ]*}} 'void'
// CHECK-NEXT: FunctionProtoType 0x{{[^ ]*}} 'void (int)' cdecl
// CHECK-NEXT: SubstTemplateTypeParmType 0x{{[^ ]*}} 'void' sugar class depth 0 index 0 U final
// CHECK-NEXT: TypeAliasTemplate 0x{{[^ ]*}} 'type1'
// CHECK-NEXT: BuiltinType 0x{{[^ ]*}} 'void'
// CHECK-NEXT: SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar class depth 0 index 0 T
// CHECK-NEXT: ClassTemplateSpecialization 0x{{[^ ]*}} 'C'
// CHECK-NEXT: BuiltinType 0x{{[^ ]*}} 'int'
} // namespace PR55886
namespace PR56099 {
template <typename... T> struct D {
template <typename... U> struct bind {
using bound_type = int(int (*...p)(T, U));
};
};
template struct D<float, char>::bind<int, short>;
// CHECK: TypeAliasDecl 0x{{[^ ]*}} <line:{{[1-9]+}}:5, col:45> col:11 bound_type 'int (int (*)(float, int), int (*)(char, short))'
// CHECK: FunctionProtoType 0x{{[^ ]*}} 'int (int (*)(float, int), int (*)(char, short))' cdecl
// CHECK: FunctionProtoType 0x{{[^ ]*}} 'int (float, int)' cdecl
// CHECK: SubstTemplateTypeParmType 0x{{[^ ]*}} 'float' sugar typename depth 0 index 0 ... T pack_index 1{{$}}
// CHECK-NEXT: ClassTemplateSpecialization 0x{{[^ ]*}} 'D'
// CHECK: SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar typename depth 0 index 0 ... U pack_index 1{{$}}
// CHECK-NEXT: ClassTemplateSpecialization 0x{{[^ ]*}} 'bind'
// CHECK: FunctionProtoType 0x{{[^ ]*}} 'int (char, short)' cdecl
// CHECK: SubstTemplateTypeParmType 0x{{[^ ]*}} 'char' sugar typename depth 0 index 0 ... T pack_index 0{{$}}
// CHECK-NEXT: ClassTemplateSpecialization 0x{{[^ ]*}} 'D'
// CHECK: SubstTemplateTypeParmType 0x{{[^ ]*}} 'short' sugar typename depth 0 index 0 ... U pack_index 0{{$}}
// CHECK-NEXT: ClassTemplateSpecialization 0x{{[^ ]*}} 'bind'
} // namespace PR56099
namespace subst_default_argument {
template<class A1> class A {};
template<template<class C1, class C2 = A<C1>> class D1, class D2> using D = D1<D2>;
template<class E1, class E2> class E {};
using test1 = D<E, int>;
// CHECK: TypeAliasDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, col:23> col:7 test1 'D<E, int>':'subst_default_argument::E<int, subst_default_argument::A<int>>'
// CHECK: TemplateSpecializationType 0x{{[^ ]*}} 'A<int>' sugar
// CHECK-NEXT: |-name: 'A':'subst_default_argument::A' qualified
// CHECK-NEXT: | `-ClassTemplateDecl {{.+}} A
// CHECK-NEXT: |-TemplateArgument type 'int'
// CHECK-NEXT: | `-SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar class depth 0 index 0 E1 final
// CHECK-NEXT: | |-ClassTemplate 0x{{[^ ]*}} 'E'
// CHECK-NEXT: | `-SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar class depth 0 index 1 D2 final
// CHECK-NEXT: | |-TypeAliasTemplate 0x{{[^ ]*}} 'D'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'int'
// CHECK-NEXT: `-RecordType 0x{{[^ ]*}} 'subst_default_argument::A<int>'
// CHECK-NEXT: `-ClassTemplateSpecialization 0x{{[^ ]*}} 'A'
} // namespace subst_default_argument
namespace D146733 {
template<class T>
T unTempl = 1;
// CHECK:VarTemplateDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:13> col:3 unTempl
// CHECK-NEXT: |-TemplateTypeParmDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:10, col:16> col:16 referenced class depth 0 index 0 T
// CHECK-NEXT: |-VarDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, col:13> col:3 unTempl 'T' cinit
// CHECK-NEXT: | `-IntegerLiteral 0x{{[^ ]*}} <col:13> 'int' 1
template<>
int unTempl<int>;
// CHECK: VarTemplateSpecializationDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:16> col:5 unTempl 'int'
// CHECK-NEXT: `-TemplateArgument type 'int'
// CHECK-NEXT: `-BuiltinType 0x{{[^ ]*}} 'int'
template<>
float unTempl<float> = 1;
// CHECK: VarTemplateSpecializationDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:24> col:7 unTempl 'float'
// CHECK-NEXT: |-TemplateArgument type 'float'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'float'
// CHECK-NEXT: `-ImplicitCastExpr 0x{{[^ ]*}} <col:24> 'float' <IntegralToFloating>
// CHECK-NEXT: `-IntegerLiteral 0x{{[^ ]*}} <col:24> 'int' 1
template<class T, class U>
T binTempl = 1;
// CHECK: VarTemplateDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:14> col:3 binTempl
// CHECK-NEXT: |-TemplateTypeParmDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:10, col:16> col:16 referenced class depth 0 index 0 T
// CHECK-NEXT: |-TemplateTypeParmDecl 0x{{[^ ]*}} <col:19, col:25> col:25 class depth 0 index 1 U
// CHECK-NEXT: |-VarDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, col:14> col:3 binTempl 'T' cinit
// CHECK-NEXT: | `-IntegerLiteral 0x{{[^ ]*}} <col:14> 'int' 1
template<class U>
int binTempl<int, U>;
// CHECK: VarTemplatePartialSpecializationDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:20> col:5 binTempl 'int'
// CHECK-NEXT: |-TemplateTypeParmDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:10, col:16> col:16 referenced class depth 0 index 0 U
// CHECK-NEXT: |-TemplateArgument type 'int'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'int'
// CHECK-NEXT: `-TemplateArgument type 'type-parameter-0-0'
// CHECK-NEXT: `-TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-0' dependent depth 0 index 0
template<class U>
float binTempl<float, U> = 1;
// CHECK: VarTemplatePartialSpecializationDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:28> col:7 binTempl 'float'
// CHECK-NEXT: |-TemplateTypeParmDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:10, col:16> col:16 referenced class depth 0 index 0 U
// CHECK-NEXT: |-TemplateArgument type 'float'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'float'
// CHECK-NEXT: |-TemplateArgument type 'type-parameter-0-0'
// CHECK-NEXT: | `-TemplateTypeParmType 0x{{[^ ]*}} 'type-parameter-0-0' dependent depth 0 index 0
// CHECK-NEXT: `-ImplicitCastExpr 0x{{[^ ]*}} <line:{{[0-9]+}}:28> 'float' <IntegralToFloating>
// CHECK-NEXT: `-IntegerLiteral 0x{{[^ ]*}} <col:28> 'int' 1
template<>
int binTempl<int, int>;
// CHECK: VarTemplateSpecializationDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:22> col:5 binTempl 'int'
// CHECK-NEXT: |-TemplateArgument type 'int'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'int'
// CHECK-NEXT: `-TemplateArgument type 'int'
// CHECK-NEXT: `-BuiltinType 0x{{[^ ]*}} 'int'
template<>
float binTempl<float, float> = 1;
// CHECK: VarTemplateSpecializationDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:1, line:{{[0-9]+}}:32> col:7 binTempl 'float'
// CHECK-NEXT: |-TemplateArgument type 'float'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'float'
// CHECK-NEXT: |-TemplateArgument type 'float'
// CHECK-NEXT: | `-BuiltinType 0x{{[^ ]*}} 'float'
// CHECK-NEXT: `-ImplicitCastExpr 0x{{[^ ]*}} <col:32> 'float' <IntegralToFloating>
// CHECK-NEXT: `-IntegerLiteral 0x{{[^ ]*}} <col:32> 'int' 1
}
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