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

187 lines
4.4 KiB
C++

// RUN: %check_clang_tidy %s bugprone-copy-constructor-init %t
class NonCopyable {
public:
NonCopyable() = default;
NonCopyable(const NonCopyable &) = delete;
private:
int a;
};
class NonCopyable2 {
public:
NonCopyable2() = default;
private:
NonCopyable2(const NonCopyable2 &);
int a;
};
class Copyable {
public:
Copyable() = default;
Copyable(const Copyable &) = default;
private:
int a;
};
class Copyable2 {
public:
Copyable2() = default;
Copyable2(const Copyable2 &) = default;
private:
int a;
};
class Copyable3 : public Copyable {
public:
Copyable3() = default;
Copyable3(const Copyable3 &) = default;
};
template <class C>
class Copyable4 {
public:
Copyable4() = default;
Copyable4(const Copyable4 &) = default;
private:
int a;
};
template <class T, class S>
class Copyable5 {
public:
Copyable5() = default;
Copyable5(const Copyable5 &) = default;
private:
int a;
};
class EmptyCopyable {
public:
EmptyCopyable() = default;
EmptyCopyable(const EmptyCopyable &) = default;
};
template <typename T>
using CopyableAlias = Copyable5<T, int>;
typedef Copyable5<int, int> CopyableAlias2;
class X : public Copyable, public EmptyCopyable {
X(const X &other) : Copyable(other) {}
};
class X2 : public Copyable2 {
X2(const X2 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor other than the copy constructor [bugprone-copy-constructor-init]
// CHECK-FIXES: X2(const X2 &other) : Copyable2(other) {}
};
class X2_A : public Copyable2 {
X2_A(const X2_A &) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X2_A(const X2_A &) {}
};
class X3 : public Copyable, public Copyable2 {
X3(const X3 &other) : Copyable(other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X3(const X3 &other) : Copyable(other) {}
};
class X4 : public Copyable {
X4(const X4 &other) : Copyable() {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X4(const X4 &other) : Copyable(other) {}
};
class X5 : public Copyable3 {
X5(const X5 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X5(const X5 &other) : Copyable3(other) {}
};
class X6 : public Copyable2, public Copyable3 {
X6(const X6 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X6(const X6 &other) : Copyable2(other), Copyable3(other) {}
};
class X7 : public Copyable, public Copyable2 {
X7(const X7 &other) : Copyable() {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X7(const X7 &other) : Copyable(other) {}
};
class X8 : public Copyable4<int> {
X8(const X8 &other) : Copyable4(other) {}
};
class X9 : public Copyable4<int> {
X9(const X9 &other) : Copyable4() {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X9(const X9 &other) : Copyable4(other) {}
};
class X10 : public Copyable4<int> {
X10(const X10 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X10(const X10 &other) : Copyable4(other) {}
};
class X11 : public Copyable5<int, float> {
X11(const X11 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X11(const X11 &other) : Copyable5(other) {}
};
class X12 : public CopyableAlias<float> {
X12(const X12 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
};
template <typename T>
class X13 : T {
X13(const X13 &other) {}
};
template class X13<EmptyCopyable>;
template class X13<Copyable>;
#define FROMMACRO \
class X14 : public Copyable2 { \
X14(const X14 &other) {} \
};
FROMMACRO
// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: calling a base constructor
class X15 : public CopyableAlias2 {
X15(const X15 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
};
class X16 : public NonCopyable {
X16(const X16 &other) {}
};
class X17 : public NonCopyable2 {
X17(const X17 &other) {}
};
class X18 : private Copyable {
X18(const X18 &other) {}
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: calling a base constructor
// CHECK-FIXES: X18(const X18 &other) : Copyable(other) {}
};
class X19 : private Copyable {
X19(const X19 &other) : Copyable(other) {}
};