[Sema] Mark ineligibility of special member functions correctly

I checked if the member function declaration was a copy constructor, but it's not sufficient; We need to check
the arguments against t

[Sema] Mark ineligibility of special member functions correctly

I checked if the member function declaration was a copy constructor, but it's not sufficient; We need to check
the arguments against the instantiated class.

Fixed https://github.com/llvm/llvm-project/issues/62555

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D149961

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[Clang] Adjust triviality computation in QualType::isTrivialType to C++20 cases.

Up to C++20, hasDefaultConstructor and !hasNonTrivialDefaultConstructor together implied
hasTrivialDefaultConstructor

[Clang] Adjust triviality computation in QualType::isTrivialType to C++20 cases.

Up to C++20, hasDefaultConstructor and !hasNonTrivialDefaultConstructor together implied
hasTrivialDefaultConstructor. In C++20, a constructor might be ineligible and can set
hasDefaultConstructor without setting hasNonTrivialDefaultConstructor.

Fix this by querying hasTrivialDefaultConstructor instead of hasDefaultConstructor.

I'd like to backport this to Clang 16.
I only change isTrivialType and in a way that should only affect code that uses
constrained constructors, so I think this is relatively safe to backport.

Fixes https://github.com/llvm/llvm-project/issues/60697

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D143891

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[Clang] Don't consider default constructors ineligible if the more constrained constructor is a template

Partially solves https://github.com/llvm/llvm-project/issues/59206:

We now mark trivial cons

[Clang] Don't consider default constructors ineligible if the more constrained constructor is a template

Partially solves https://github.com/llvm/llvm-project/issues/59206:

We now mark trivial constructors as eligible even if there's a more constrained templated default constructor. Although technically non-conformant, this solves problems with pretty reasonable uses cases like
```
template<int n>
struct Foo {
constexpr Foo() = default;

template<class... Ts>
Foo(Ts... vals) requires(sizeof...(Ts) == n) {}
};
```
where we currently consider the default constructor to be ineligible and therefor inheriting/containing classes have non trivial constructors. This is aligned with GCC: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=c75ebe76ae12ac4020f20a24f34606a594a40d15

This doesn't change `__is_trivial`. Although we're technically standard conformant in this regard, GCC/MSVC exhibit different behaviors that seem to make more sense. An issue has been filed to CWG and we await their response.

Reviewed By: erichkeane, #clang-language-wg

Differential Revision: https://reviews.llvm.org/D139038

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Re-apply "Deferred Concept Instantiation Implementation"

This reverts commit 95d94a67755620c0a2871ac6f056ca8e9731d5e9.

This implements the deferred concepts instantiation, which should allow
the li

Re-apply "Deferred Concept Instantiation Implementation"

This reverts commit 95d94a67755620c0a2871ac6f056ca8e9731d5e9.

This implements the deferred concepts instantiation, which should allow
the libstdc++ ranges to properly compile, and for the CRTP to work for
constrained functions.

Since the last attempt, this has fixed the issues from @wlei and
@mordante.

Differential Revision: https://reviews.llvm.org/D126907

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[Clang] Implement P0848 (Conditionally Trivial Special Member Functions)

This patch implements P0848 in Clang.

During the instantiation of a C++ class, in `Sema::ActOnFields`, we evaluate constrain

[Clang] Implement P0848 (Conditionally Trivial Special Member Functions)

This patch implements P0848 in Clang.

During the instantiation of a C++ class, in `Sema::ActOnFields`, we evaluate constraints for all the SMFs and compare the constraints to compute the eligibility. We defer the computation of the type's [copy-]trivial bits from addedMember to the eligibility computation, like we did for destructors in D126194. `canPassInRegisters` is modified as well to better respect the ineligibility of functions.

Note: Because of the non-implementation of DR1734 and DR1496, I treat deleted member functions as 'eligible' for the purpose of [copy-]triviallity. This is unfortunate, but I couldn't think of a way to make this make sense otherwise.

Reviewed By: #clang-language-wg, cor3ntin, aaron.ballman

Differential Revision: https://reviews.llvm.org/D128619

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[Clang] Implement P0848 (Conditionally Trivial Special Member Functions)

This patch implements P0848 in Clang.

During the instantiation of a C++ class, in `Sema::ActOnFields`, we evaluate constrain

[Clang] Implement P0848 (Conditionally Trivial Special Member Functions)

This patch implements P0848 in Clang.

During the instantiation of a C++ class, in `Sema::ActOnFields`, we evaluate constraints for all the SMFs and compare the constraints to compute the eligibility. We defer the computation of the type's [copy-]trivial bits from addedMember to the eligibility computation, like we did for destructors in D126194. `canPassInRegisters` is modified as well to better respect the ineligibility of functions.

Note: Because of the non-implementation of DR1734 and DR1496, I treat deleted member functions as 'eligible' for the purpose of [copy-]triviallity. This is unfortunate, but I couldn't think of a way to make this make sense otherwise.

Reviewed By: #clang-language-wg, cor3ntin, aaron.ballman

Differential Revision: https://reviews.llvm.org/D128619

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