[NFC] Start saving InstantiatedFromDecl in non-template functions

In cases where a non-template function is defined inside a function
template, we don't have information about the original uninstant

[NFC] Start saving InstantiatedFromDecl in non-template functions

In cases where a non-template function is defined inside a function
template, we don't have information about the original uninstantiated
version. In the case of concepts instantiation, we will need the
ability to get back to the original template. This patch splits a piece
of the deferred concepts instantaition patch off to accomplish the
storage of this, with minor runtime overhead, and zero additional
storage.

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Revert "Re-apply "Deferred Concept Instantiation Implementation"""

This reverts commit befa8cf087dbb8159a4d9dc8fa4d6748d6d5049a.

Apparently this breaks some libc++ builds with an apparent assertion

Revert "Re-apply "Deferred Concept Instantiation Implementation"""

This reverts commit befa8cf087dbb8159a4d9dc8fa4d6748d6d5049a.

Apparently this breaks some libc++ builds with an apparent assertion,
so I'm looking into that .

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Re-apply "Deferred Concept Instantiation Implementation""

This reverts commit d4d47e574ecae562ab32f8ac7fa3f4d424bb6574.

This fixes the lldb crash that was observed by ensuring that our
friend-'temp

Re-apply "Deferred Concept Instantiation Implementation""

This reverts commit d4d47e574ecae562ab32f8ac7fa3f4d424bb6574.

This fixes the lldb crash that was observed by ensuring that our
friend-'template contains reference to' TreeTransform properly handles a
TemplateDecl.

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Revert "Deferred Concept Instantiation Implementation"

This reverts commit 2f207439521d62d9551b2884158368e8b34084e5 because it
triggers an assertion when building an LLDB test program:

Assertion

Revert "Deferred Concept Instantiation Implementation"

This reverts commit 2f207439521d62d9551b2884158368e8b34084e5 because it
triggers an assertion when building an LLDB test program:

Assertion failed: (InstantiatingSpecializations.empty() && "failed to
clean up an InstantiatingTemplate?"), function ~Sema, file
/Users/buildslave/jenkins/workspace/lldb-cmake/llvm-project/clang/lib/Sema/Sema.cpp,
line 458.

More details in https://reviews.llvm.org/D126907.

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Deferred Concept Instantiation Implementation

This is a continuation of D119544. Based on @rsmith 's feed back
showing me https://eel.is/c++draft/temp#friend-9, We should properly
handle friend fun

Deferred Concept Instantiation Implementation

This is a continuation of D119544. Based on @rsmith 's feed back
showing me https://eel.is/c++draft/temp#friend-9, We should properly
handle friend functions now.

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

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[C++20] [Module] Support reachable definition initially/partially

This patch introduces a new kind of ModuleOwnershipKind as
ReachableWhenImported. This intended the status for reachable described
a

[C++20] [Module] Support reachable definition initially/partially

This patch introduces a new kind of ModuleOwnershipKind as
ReachableWhenImported. This intended the status for reachable described
at: https://eel.is/c++draft/module.reach#3.

Note that this patch is not intended to support all semantics about
reachable semantics. For example, this patch didn't implement discarded
declarations in GMF. (https://eel.is/c++draft/module.global.frag#3).

This fixes: https://bugs.llvm.org/show_bug.cgi?id=52281 and
https://godbolt.org/z/81f3ocjfW.

Reviewed By: rsmith, iains

Differential Revision: https://reviews.llvm.org/D113545

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Revert "[C++20] [Modules] Implement Reachable initiallly"

This reverts commit a223ba0a697c1598b434cf2495c9cd9ec5640fc7.

The previous commit don't contain additional information, which is bad.

[C++20] [Modules] Implement Reachable initiallly

Revert ""Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation"""""

This reverts commit a425cac31e2e4cee8e14b7b9a99c8ba17c1ebb52.

There is another libc++ test, that this time causes us

Revert ""Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation"""""

This reverts commit a425cac31e2e4cee8e14b7b9a99c8ba17c1ebb52.

There is another libc++ test, that this time causes us to hit an
assertion. Reverting, likely for a while this time.

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"Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation""""

This includes a fix for the libc++ issue I ran across with friend
declarations not properly being identified as overloads.

Th

"Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation""""

This includes a fix for the libc++ issue I ran across with friend
declarations not properly being identified as overloads.

This reverts commit 45c07db31cc76802a1a2e41bed1ce9c1b8198181.

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Revert "Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation"""

This reverts commit a97899108e495147985e5e9492e742d51d5cc97a.

The patch caused some problems with the libc++ `__range_a

Revert "Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation"""

This reverts commit a97899108e495147985e5e9492e742d51d5cc97a.

The patch caused some problems with the libc++ `__range_adaptor_closure`
that I haven't been able to figure out the cause of, so I am reverting
while I figure out whether this is a solvable problem/issue with the
CFE, or libc++ depending on an older 'incorrect' behavior.

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Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation""

This reverts commit 0c31da48389754822dc3eecc4723160c295b9ab2.

I've solved the issue with the PointerUnion by making the
`Functio

Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation""

This reverts commit 0c31da48389754822dc3eecc4723160c295b9ab2.

I've solved the issue with the PointerUnion by making the
`FunctionTemplateDecl` pointer be a NamedDecl, that could be a
`FunctionDecl` or `FunctionTemplateDecl` depending. This is enforced
with an assert.

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Revert "Deferred Concept Instantiation Implementation"

This reverts commit 4b6c2cd647e9e5a147954886338f97ffb6a1bcfb.

The patch caused numerous ARM 32 bit build failures, since we added a
5th item t

Revert "Deferred Concept Instantiation Implementation"

This reverts commit 4b6c2cd647e9e5a147954886338f97ffb6a1bcfb.

The patch caused numerous ARM 32 bit build failures, since we added a
5th item to the PointerUnion, and went over the 2-bits available in the
32 bit pointers.

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Deferred Concept Instantiation Implementation

As reported here: https://github.com/llvm/llvm-project/issues/44178

Concepts are not supposed to be instantiated until they are checked, so
this patch

Deferred Concept Instantiation Implementation

As reported here: https://github.com/llvm/llvm-project/issues/44178

Concepts are not supposed to be instantiated until they are checked, so
this patch implements that and goes through significant amounts of work
to make sure we properly re-instantiate the concepts correctly.

Differential Revision: https://reviews.llvm.org/D119544

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[Serialization] write expr dependence bits as a single integer

When exprs are written unabbreviated:
- these were encoded as 5 x vbr6 = 30 bits
- now they fit exactly into a one-chunk vbr = 6 bi

[Serialization] write expr dependence bits as a single integer

When exprs are written unabbreviated:
- these were encoded as 5 x vbr6 = 30 bits
- now they fit exactly into a one-chunk vbr = 6 bits

clangd --check=clangd/AST.cpp reports ~1% reduction in PCH size
(42826720->42474460)

Differential Revision: https://reviews.llvm.org/D124250

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[C++20] [Modules] Don't generate strong function of a partition in importing modules

This solves the multiple defintiion issue
https://github.com/llvm/llvm-project/issues/54269.

I think the cause o

[C++20] [Modules] Don't generate strong function of a partition in importing modules

This solves the multiple defintiion issue
https://github.com/llvm/llvm-project/issues/54269.

I think the cause of the bug might be an oversight. We just forget to
edit this when implementing partitions. And it should be a good fix.

Reviewed By: iains

Differential Revision: https://reviews.llvm.org/D121271

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[Clang] Implement __builtin_source_location.

This builtin returns the address of a global instance of the
`std::source_location::__impl` type, which must be defined (with an
appropriate shape) befor

[Clang] Implement __builtin_source_location.

This builtin returns the address of a global instance of the
`std::source_location::__impl` type, which must be defined (with an
appropriate shape) before calling the builtin.

It will be used to implement std::source_location in libc++ in a
future change. The builtin is compatible with GCC's implementation,
and libstdc++'s usage. An intentional divergence is that GCC declares
the builtin's return type to be `const void*` (for
ease-of-implementation reasons), while Clang uses the actual type,
`const std::source_location::__impl*`.

In order to support this new functionality, I've also added a new
'UnnamedGlobalConstantDecl'. This artificial Decl is modeled after
MSGuidDecl, and is used to represent a generic concept of an lvalue
constant with global scope, deduplicated by its value. It's possible
that MSGuidDecl itself, or some of the other similar sorts of things
in Clang might be able to be refactored onto this more-generic
concept, but there's enough special-case weirdness in MSGuidDecl that
I gave up attempting to share code there, at least for now.

Finally, for compatibility with libstdc++'s <source_location> header,
I've added a second exception to the "cannot cast from void* to T* in
constant evaluation" rule. This seems a bit distasteful, but feels
like the best available option.

Reviewers: aaron.ballman, erichkeane

Differential Revision: https://reviews.llvm.org/D120159

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Use llvm::append_range instead of push_back loops where applicable. NFCI.

[clang] Allocate 2 bits to store the constexpr specifier kind when serializing

Now that consteval and constinit are possible values, 1 bit
is no longer enough.

Fixes https://github.com/clangd/clang

[clang] Allocate 2 bits to store the constexpr specifier kind when serializing

Now that consteval and constinit are possible values, 1 bit
is no longer enough.

Fixes https://github.com/clangd/clangd/issues/887

Differential Revision: https://reviews.llvm.org/D111971

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[clang] p1099 using enum part 2

This implements the 'using enum maybe-qualified-enum-tag ;' part of
1099. It introduces a new 'UsingEnumDecl', subclassed from
'BaseUsingDecl'. Much of the diff is th

[clang] p1099 using enum part 2

This implements the 'using enum maybe-qualified-enum-tag ;' part of
1099. It introduces a new 'UsingEnumDecl', subclassed from
'BaseUsingDecl'. Much of the diff is the boilerplate needed to get the
new class set up.

There is one case where we accept ill-formed, but I believe this is
merely an extended case of an existing bug, so consider it
orthogonal. AFAICT in class-scope the c++20 rule is that no 2 using
decls can bring in the same target decl ([namespace.udecl]/8). But we
already accept:

struct A { enum { a }; };
struct B : A { using A::a; };
struct C : B { using A::a;
using B::a; }; // same enumerator

this patch permits mixtures of 'using enum Bob;' and 'using Bob::member;' in the same way.

Differential Revision: https://reviews.llvm.org/D102241

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[clang] Implement the using_if_exists attribute

This attribute applies to a using declaration, and permits importing a
declaration without knowing if that declaration exists. This is useful
for libc

[clang] Implement the using_if_exists attribute

This attribute applies to a using declaration, and permits importing a
declaration without knowing if that declaration exists. This is useful
for libc++ C wrapper headers that re-export declarations in std::, in
cases where the base C library doesn't provide all declarations.

This attribute was proposed in http://lists.llvm.org/pipermail/cfe-dev/2020-June/066038.html.

rdar://69313357

Differential Revision: https://reviews.llvm.org/D90188

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Treat implicit deduction guides as being equivalent to their
corresponding constructor for access checking purposes.

[clang] Spell correct variable

fix Trailling -> Trailing (two ll-> one l)

Differential Revision: https://reviews.llvm.org/D101753

Make iteration over the DeclContext::lookup_result safe.

The idiom:
```
DeclContext::lookup_result R = DeclContext::lookup(Name);
for (auto *D : R) {...}
```

is not safe when in the loop body we tr

Make iteration over the DeclContext::lookup_result safe.

The idiom:
```
DeclContext::lookup_result R = DeclContext::lookup(Name);
for (auto *D : R) {...}
```

is not safe when in the loop body we trigger deserialization from an AST file.
The deserialization can insert new declarations in the StoredDeclsList whose
underlying type is a vector. When the vector decides to reallocate its storage
the pointer we hold becomes invalid.

This patch replaces a SmallVector with an singly-linked list. The current
approach stores a SmallVector<NamedDecl*, 4> which is around 8 pointers.
The linked list is 3, 5, or 7. We do better in terms of memory usage for small
cases (and worse in terms of locality -- the linked list entries won't be near
each other, but will be near their corresponding declarations, and we were going
to fetch those memory pages anyway). For larger cases: the vector uses a
doubling strategy for reallocation, so will generally be between half-full and
full. Let's say it's 75% full on average, so there's N * 4/3 + 4 pointers' worth
of space allocated currently and will be 2N pointers with the linked list. So we
break even when there are N=6 entries and slightly lose in terms of memory usage
after that. We suspect that's still a win on average.

Thanks to @rsmith!

Differential revision: https://reviews.llvm.org/D91524

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Revert "[NFC, Refactor] Modernize StorageClass from Specifiers.h to a scoped enum (II)"

This reverts commit efc82c4ad2bcb256a4f4c20238d08cd3afba4d2d.