[Clang] Implement __builtin_source_location.

[jyknight]

Summary

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.

[aaron.ballman]

Thank you for this! I've got some initial comments on it.

Btw, I think there may be some functionality missing for AST dumping, so I'd like to see some additional tests for that.

clang/docs/LanguageExtensions.rst

3437–3438

Doesn't the type for <any-integral-type> matter though, due to layout differences based on the size of the integer type picked?

Also, a downside of requiring this type to be defined before the builtin can be used is that this builtin would otherwise be suitable in C, but there's no way to name that particular type. Is there anything we can do to keep this builtin generic enough to be used in C as well?

clang/include/clang/AST/DeclCXX.h

4209

4210

I presume this is what was meant, right?

4239

printName() in a class named UnnamedGlobalConstantDecl (which isn't a NamedDecl) seems a bit confusing as to what this actually prints.

Also, what is this overriding? NamedDecl has a virtual printName() function, but ValueDecl does not. I have the sneaking suspicion that this can be removed.

clang/include/clang/AST/Expr.h

4710

Should this also be marked LLVM_READONLY as in the original interface?

clang/include/clang/Basic/DiagnosticSemaKinds.td

11560–11563

clang/include/clang/Serialization/ASTBitCodes.h

44

Do we need to bump this value now that we have a new kind of AST node?

clang/lib/AST/Expr.cpp

2231

Under what conditions can Context be null? (should this be a dyn_cast instead?)

clang/lib/AST/ExprClassification.cpp

467–468

Plus fix the formatting that I'm sure I broke.

467–472

clang/lib/AST/ExprConstant.cpp

1982–1983

8846–8848

Do we want to be even more restrictive here and tie it to libstdc++ (e.g., like we did in https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaDeclCXX.cpp#L12352)

clang/lib/Sema/SemaExpr.cpp

3295

Spurious indentation change?

3443

Perhaps stupid question, but do we want this to be an lvalue as opposed to a prvalue?

14131–14134

Might as well combine these as well.

16325

16372

I would set the count to 5 instead of 0 because otherwise someone could do something stupid like:

namespace std {
struct source_location {
  struct __impl {
    int Muahahahahhahaha;
    // ... The other four fields.
  };
};
}

clang/lib/Sema/SemaTemplate.cpp

7012–7015

clang/test/SemaCXX/source_location.cpp

383–388

Why are these commented out?

[aaron.ballman]

Ah, one more thing I missed -- you should add a release note for this functionality.

[jyknight]

Minor tweaks to comments and docs.

[jyknight]

Update per review comments.

[jyknight]

In D120159#3341224, @aaron.ballman wrote:

Btw, I think there may be some functionality missing for AST dumping, so I'd like to see some additional tests for that.

I'm not sure what test would actually show a problem (or lack thereof) in the ast dumping -- AFAICT, UnnamedGlobalConstantDecl can't actually show up in an AST dump at the moment. The AST generated for a __builtin_source_location call doesn't contain one, since it's only when evaluating the value that you receive an LValue pointing to an UnnamedGlobalConstantDecl. But https://github.com/llvm/llvm-project/blob/fdfe26ddbeb1a5eb6106a6a27d6f8240deca543f/clang/lib/AST/TextNodeDumper.cpp#L535 doesn't print those usefully, anyhow.

clang/docs/LanguageExtensions.rst

3437–3438

The type of the integer (as well as ordering of the fields) doesn't matter, because the code populates fields in the actual struct layout as defined, it doesn't assume a particular layout.

As for making it usable from C code, possibly we could have it attempt to look-up a __source_location_impl type in C mode (or maybe always, as a fallback if std::source_location::__impl doesn't exist).

But, that's something we could add later if needed -- and before going that route, I think we should discuss with GCC/libstdc++ to try to remain compatible.

clang/include/clang/AST/DeclCXX.h

4210

Yep.

4239

class ValueDecl : public NamedDecl -- so, UnnamedGlobalConstantDecl _is_ a "NamedDecl". I suspect it's not strictly needed, but it does affect what's printed in debug output for this type.

clang/include/clang/AST/Expr.h

4710

I don't think it'd actually make a difference, and we don't typically go around annotating everything with that attribute. It was weird that isStringType wasn't annotated but isIntType was, in the first place.

clang/include/clang/Serialization/ASTBitCodes.h

44

Probably so. It looks like we don't generally bump this number, but that's probably accidental.

clang/lib/AST/Expr.cpp

2231

That came from the similar code above for __builtin_FUNCTION. I don't think it can actually be null (in either place). Changed in both.

clang/lib/AST/ExprConstant.cpp

8846–8848

I don't see anything in the code you linked that makes it libstdc++-tied? But, in any case, I think restricting to std::source_location::current is sufficiently narrow that it doesn't much matter.

We also have the option of not doing this hack, since it's going to be fixed in libstdc++. However, given that a similar hack is already present for std::allocator, extending it to source_location doesn't seem that terrible.

(And IMO, it would make sense for the C++ standard to actually permit this in constant evaluation, anyways...)

clang/lib/Sema/SemaExpr.cpp

3443

I think so? I was thinking of it as acting effectively like a string literal.

clang/test/SemaCXX/source_location.cpp

383–388

Oops -- intended to update those to the proper strings. Fixed.

[aaron.ballman]

In D120159#3348927, @jyknight wrote:

In D120159#3341224, @aaron.ballman wrote:

Btw, I think there may be some functionality missing for AST dumping, so I'd like to see some additional tests for that.

I'm not sure what test would actually show a problem (or lack thereof) in the ast dumping -- AFAICT, UnnamedGlobalConstantDecl can't actually show up in an AST dump at the moment. The AST generated for a __builtin_source_location call doesn't contain one, since it's only when evaluating the value that you receive an LValue pointing to an UnnamedGlobalConstantDecl. But https://github.com/llvm/llvm-project/blob/fdfe26ddbeb1a5eb6106a6a27d6f8240deca543f/clang/lib/AST/TextNodeDumper.cpp#L535 doesn't print those usefully, anyhow.

Ah, okay, that's a good point. I was thinking this would show up in the AST in places like:

template <typename Ty>
auto func() -> Ty;

int main() {
  func<decltype(__builtin_source_location())>();
}

when we go to print the Ty type from the template. Does that not happen?

clang/docs/LanguageExtensions.rst

3437–3438

Okay, I'm fine adding that support later; I definitely agree about the compatibility concerns.

clang/include/clang/AST/DeclCXX.h

4239

How the heck did I miss that? Sorry for the noise.

clang/include/clang/AST/Expr.h

4710

SGTM

clang/lib/AST/ExprConstant.cpp

8846–8848

I'm fine adding the hack, but the restrictions I was thinking of was forcing it to only work in a system header.

clang/lib/Sema/SemaExpr.cpp

3443

I was thinking the same thing, but I had thought string literals were a prvalue the same as integer literals, oops. :-)

[jyknight]

In D120159#3349069, @aaron.ballman wrote:

Ah, okay, that's a good point. I was thinking this would show up in the AST in places like:

template <typename Ty>
auto func() -> Ty;

int main() {
  func<decltype(__builtin_source_location())>();
}

when we go to print the Ty type from the template. Does that not happen?

|-FunctionTemplateDecl 0x10ef3288 <line:11:1, line:12:16> col:6 func
| |-TemplateTypeParmDecl 0x10ef3068 <line:11:11, col:20> col:20 referenced typename depth 0 index 0 Ty
| |-FunctionDecl 0x10ef31e8 <line:12:1, col:16> col:6 func 'auto () -> Ty'
| `-FunctionDecl 0x10ef36d8 <col:1, col:16> col:6 used func 'auto () -> const std::source_location::__impl *'
|   `-TemplateArgument type 'const std::source_location::__impl *'
|     `-PointerType 0x10ef34c0 'const std::source_location::__impl *'
|       `-QualType 0x10ef2d81 'const std::source_location::__impl' const
|         `-RecordType 0x10ef2d80 'std::source_location::__impl'
|           `-CXXRecord 0x10ef2ce8 '__impl'
`-FunctionDecl 0x10ef33f0 <line:14:1, line:16:1> line:14:5 main 'int ()'
  `-CompoundStmt 0x10ef38c0 <col:12, line:16:1>
    `-CallExpr 0x10ef38a0 <line:15:3, col:47> 'const std::source_location::__impl *':'const std::source_location::__impl *'
      `-ImplicitCastExpr 0x10ef3888 <col:3, col:45> 'auto (*)() -> const std::source_location::__impl *' <FunctionToPointerDecay>
        `-DeclRefExpr 0x10ef37d0 <col:3, col:45> 'auto () -> const std::source_location::__impl *' lvalue Function 0x10ef36d8 'func' 'auto () -> const std::source_location::__impl *' (FunctionTemplate 0x10ef3288 'func')

The type is simply const std::source_location::__impl*. Only the evaluated value refers to an UnnamedGlobalConstantDecl.

If it was possible to use in a non-type template argument, I think you could get it to show up in the AST for the instantiation, but that's not supported. E.g.

template <auto T = __builtin_source_location()>
    class X {};

X<> x;

Results in:

test.cc:12:20: error: non-type template argument does not refer to any declaration
template <auto T = __builtin_source_location()>
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cc:15:3: note: while checking a default template argument used here
X<> x;
~~^

clang/lib/AST/ExprConstant.cpp

8846–8848

Oh, I see. That doesn't seem important here, since non-system code should not be defining a std::source_location::current() function anyhow.

(But if we keep needing to add exceptions here, maybe eventually we just decide to just turn this error into a default-on warningerror, and not diagnose it in system headers.)

[aaron.ballman]

In D120159#3349271, @jyknight wrote:

In D120159#3349069, @aaron.ballman wrote:

Ah, okay, that's a good point. I was thinking this would show up in the AST in places like:

template <typename Ty>
auto func() -> Ty;

int main() {
  func<decltype(__builtin_source_location())>();
}

when we go to print the Ty type from the template. Does that not happen?

|-FunctionTemplateDecl 0x10ef3288 <line:11:1, line:12:16> col:6 func
| |-TemplateTypeParmDecl 0x10ef3068 <line:11:11, col:20> col:20 referenced typename depth 0 index 0 Ty
| |-FunctionDecl 0x10ef31e8 <line:12:1, col:16> col:6 func 'auto () -> Ty'
| `-FunctionDecl 0x10ef36d8 <col:1, col:16> col:6 used func 'auto () -> const std::source_location::__impl *'
|   `-TemplateArgument type 'const std::source_location::__impl *'
|     `-PointerType 0x10ef34c0 'const std::source_location::__impl *'
|       `-QualType 0x10ef2d81 'const std::source_location::__impl' const
|         `-RecordType 0x10ef2d80 'std::source_location::__impl'
|           `-CXXRecord 0x10ef2ce8 '__impl'
`-FunctionDecl 0x10ef33f0 <line:14:1, line:16:1> line:14:5 main 'int ()'
  `-CompoundStmt 0x10ef38c0 <col:12, line:16:1>
    `-CallExpr 0x10ef38a0 <line:15:3, col:47> 'const std::source_location::__impl *':'const std::source_location::__impl *'
      `-ImplicitCastExpr 0x10ef3888 <col:3, col:45> 'auto (*)() -> const std::source_location::__impl *' <FunctionToPointerDecay>
        `-DeclRefExpr 0x10ef37d0 <col:3, col:45> 'auto () -> const std::source_location::__impl *' lvalue Function 0x10ef36d8 'func' 'auto () -> const std::source_location::__impl *' (FunctionTemplate 0x10ef3288 'func')

The type is simply const std::source_location::__impl*. Only the evaluated value refers to an UnnamedGlobalConstantDecl.

If it was possible to use in a non-type template argument, I think you could get it to show up in the AST for the instantiation, but that's not supported. E.g.

template <auto T = __builtin_source_location()>
    class X {};

X<> x;

Results in:

test.cc:12:20: error: non-type template argument does not refer to any declaration
template <auto T = __builtin_source_location()>
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cc:15:3: note: while checking a default template argument used here
X<> x;
~~^

Excellent, thank you for double-checking! This does raise an interesting question about the AST import functionality -- if UnnamedGlobalConstantDecl can't show up in the AST, do we need to handle AST reading and writing for it, or can we assert that it should never show up through PCH/Modules?

In general, this is looking pretty good to me. Adding Erich in case he spots something I missed.

clang/lib/AST/ExprConstant.cpp

8846–8848

okay, that's fair.

[jyknight]

Fix and test __impl lookup within the definition of std::source_location.

[jyknight]

Ping; any more comments?

[aaron.ballman]

LGTM!

[erichkeane]

no comments, looks fine to me. Thanks!

[kda]

This appears to have broken buildbot: sanitizer-x86_64-linux-fast

Validating if reversion clears it up.

Then will revert.

[jyknight]

In D120159#3415112, @kda wrote:

This appears to have broken buildbot: sanitizer-x86_64-linux-fast

Validating if reversion clears it up.

Then will revert.

Fixed by 8f66f1371981bda1af1ca43d505e1bc5836b3e36 I believe.

[kda]

Fix looks good. Thank you.

clang/docs/LanguageExtensions.rst

 Note that there is no builtin matching the `llvm.coro.save` intrinsic. LLVM
 automatically will insert one if the first argument to `llvm.coro.suspend` is
 token `none`. If a user calls `__builin_suspend`, clang will insert `token none`
 as the first argument to the intrinsic.
 
 Source location builtins
 ------------------------
 
-Clang provides experimental builtins to support C++ standard library implementation
-of ``std::experimental::source_location`` as specified in  http://wg21.link/N4600.
-With the exception of ``__builtin_COLUMN``, these builtins are also implemented by
-GCC.
+Clang provides builtins to support C++ standard library implementation
+of ``std::source_location`` as specified in C++20.  With the exception
+of ``__builtin_COLUMN``, these builtins are also implemented by GCC.
 
 **Syntax**:
 
 .. code-block:: c
 
   const char *__builtin_FILE();
   const char *__builtin_FUNCTION();
   unsigned    __builtin_LINE();
   unsigned    __builtin_COLUMN(); // Clang only
+  const std::source_location::__impl *__builtin_source_location();
 
 **Example of use**:
 
 .. code-block:: c++
 
   void my_assert(bool pred, int line = __builtin_LINE(), // Captures line of caller
                  const char* file = __builtin_FILE(),
                  const char* function = __builtin_FUNCTION()) {
.. code-block:: c++
 
   struct MyClassType {
     int line = __builtin_LINE(); // captures line of the constructor used during initialization
     constexpr MyClassType(int) { assert(line == __LINE__); }
   };
 
 **Description**:
 
-The builtins ``__builtin_LINE``, ``__builtin_FUNCTION``, and ``__builtin_FILE`` return
-the values, at the "invocation point", for ``__LINE__``, ``__FUNCTION__``, and
-``__FILE__`` respectively. These builtins are constant expressions.
+The builtins ``__builtin_LINE``, ``__builtin_FUNCTION``, and ``__builtin_FILE``
+return the values, at the "invocation point", for ``__LINE__``,
+``__FUNCTION__``, and ``__FILE__`` respectively. ``__builtin_COLUMN`` similarly
+returns the column, though there is no corresponding macro. These builtins are
+constant expressions.
 
 When the builtins appear as part of a default function argument the invocation
 point is the location of the caller. When the builtins appear as part of a
 default member initializer, the invocation point is the location of the
 constructor or aggregate initialization used to create the object. Otherwise
 the invocation point is the same as the location of the builtin.
 
 When the invocation point of ``__builtin_FUNCTION`` is not a function scope the
 empty string is returned.
 
+The builtin ``__builtin_source_location`` returns a pointer to constant static
+data of type ``std::source_location::__impl``. This type must have already been
+defined, and must contain exactly four fields: ``const char *_M_file_name``,
+``const char *_M_function_name``, ``<any-integral-type> _M_line``, and
+``<any-integral-type> _M_column``. The fields will be populated in the same
+manner as the above four builtins, except that ``_M_function_name`` is populated
+with ``__PRETTY_FUNCTION__`` rather than ``__FUNCTION__``.
+
+
 Alignment builtins
 ------------------
 Clang provides builtins to support checking and adjusting alignment of
 pointers and integers.
 These builtins can be used to avoid relying on implementation-defined behavior
 of arithmetic on integers derived from pointers.
 Additionally, these builtins retain type information and, unlike bitwise
 arithmetic, they can perform semantic checking on the alignment value.

clang/docs/ReleaseNotes.rst

 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 - Diagnose consteval and constexpr issues that happen at namespace scope. This
   partially addresses `Issue 51593 <https://github.com/llvm/llvm-project/issues/51593>`_.
 - No longer attempt to evaluate a consteval UDL function call at runtime when
   it is called through a template instantiation. This fixes
   `Issue 54578 <https://github.com/llvm/llvm-project/issues/54578>`_.
 
+- Implemented `__builtin_source_location()` which enables library support for std::source_location.
+
 C++2b Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 
 - Implemented `P2128R6: Multidimensional subscript operator <https://wg21.link/P2128R6>`_.
 - Implemented `P0849R8: auto(x): decay-copy in the language <https://wg21.link/P0849R8>`_.
 - Implemented `P2242R3: Non-literal variables (and labels and gotos) in constexpr functions <https://wg21.link/P2242R3>`_.
 
 CUDA Language Changes in Clang

clang/include/clang/AST/ASTContext.h

class ASTContext : public RefCountedBase<ASTContext> {
   llvm::DenseMap<const ObjCMethodDecl*,const ObjCMethodDecl*> ObjCMethodRedecls;
 
   /// Mapping from __block VarDecls to BlockVarCopyInit.
   llvm::DenseMap<const VarDecl *, BlockVarCopyInit> BlockVarCopyInits;
 
   /// Mapping from GUIDs to the corresponding MSGuidDecl.
   mutable llvm::FoldingSet<MSGuidDecl> MSGuidDecls;
 
+  /// Mapping from APValues to the corresponding UnnamedGlobalConstantDecl.
+  mutable llvm::FoldingSet<UnnamedGlobalConstantDecl>
+      UnnamedGlobalConstantDecls;
+
   /// Mapping from APValues to the corresponding TemplateParamObjects.
   mutable llvm::FoldingSet<TemplateParamObjectDecl> TemplateParamObjectDecls;
 
   /// A cache mapping a string value to a StringLiteral object with the same
   /// value.
   ///
   /// This is lazily created.  This is intentionally not serialized.
   mutable llvm::StringMap<StringLiteral *> StringLiteralCache;
public:
   /// function declaration or file name. Used by SourceLocExpr and
   /// PredefinedExpr to cache evaluated results.
   StringLiteral *getPredefinedStringLiteralFromCache(StringRef Key) const;
 
   /// Return a declaration for the global GUID object representing the given
   /// GUID value.
   MSGuidDecl *getMSGuidDecl(MSGuidDeclParts Parts) const;
 
+  /// Return a declaration for a uniquified anonymous global constant
+  /// corresponding to a given APValue.
+  UnnamedGlobalConstantDecl *
+  getUnnamedGlobalConstantDecl(QualType Ty, const APValue &Value) const;
+
   /// Return the template parameter object of the given type with the given
   /// value.
   TemplateParamObjectDecl *getTemplateParamObjectDecl(QualType T,
                                                       const APValue &V) const;
 
   /// Parses the target attributes passed in, and returns only the ones that are
   /// valid feature names.
   ParsedTargetAttr filterFunctionTargetAttrs(const TargetAttr *TD) const;

clang/include/clang/AST/DeclCXX.h

static void Profile(llvm::FoldingSetNodeID &ID, Parts P) {
     ID.AddInteger(P.getPart4And5AsUint64());
   }
   void Profile(llvm::FoldingSetNodeID &ID) { Profile(ID, PartVal); }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Decl::MSGuid; }
 };
 
+/// An artificial decl, representing a global anonymous constant value which is
+/// uniquified by value within a translation unit.
+///
+/// These is currently only used to back the LValue returned by
+/// __builtin_source_location, but could potentially be used for other similar
+/// situations in the future.
+class UnnamedGlobalConstantDecl : public ValueDecl,
+                                  public Mergeable<UnnamedGlobalConstantDecl>,
+                                  public llvm::FoldingSetNode {
+
+  // The constant value of this global.
+  APValue Value;
+
+  void anchor() override;
+
+  UnnamedGlobalConstantDecl(DeclContext *DC, QualType T, const APValue &Val);
+
+  static UnnamedGlobalConstantDecl *Create(const ASTContext &C, QualType T,
+                                           const APValue &APVal);
+  static UnnamedGlobalConstantDecl *CreateDeserialized(ASTContext &C,
+                                                       unsigned ID);
+
+  // Only ASTContext::getUnnamedGlobalConstantDecl and deserialization create
+  // these.
+  friend class ASTContext;
+  friend class ASTReader;
+  friend class ASTDeclReader;
+
+public:
+  /// Print this in a human-readable format.
+  void printName(llvm::raw_ostream &OS) const override;
+
+  const APValue &getValue() const { return Value; }
+
+  static void Profile(llvm::FoldingSetNodeID &ID, QualType Ty,
+                      const APValue &APVal) {
+    Ty.Profile(ID);
+    APVal.Profile(ID);
+  }
+  void Profile(llvm::FoldingSetNodeID &ID) {
+    Profile(ID, getType(), getValue());
+  }
+
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) { return K == Decl::UnnamedGlobalConstant; }
+};
+
 /// Insertion operator for diagnostics.  This allows sending an AccessSpecifier
 /// into a diagnostic with <<.
 const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
                                       AccessSpecifier AS);
 
 } // namespace clang
 
 #endif // LLVM_CLANG_AST_DECLCXX_H

clang/include/clang/AST/Expr.h

public:
   // Iterators
   child_range children() { return child_range(&Val, &Val+1); }
   const_child_range children() const {
     return const_child_range(&Val, &Val + 1);
   }
 };
 
 /// Represents a function call to one of __builtin_LINE(), __builtin_COLUMN(),
-/// __builtin_FUNCTION(), or __builtin_FILE().
+/// __builtin_FUNCTION(), __builtin_FILE(), or __builtin_source_location().
 class SourceLocExpr final : public Expr {
   SourceLocation BuiltinLoc, RParenLoc;
   DeclContext *ParentContext;
 
 public:
-  enum IdentKind { Function, File, Line, Column };
+  enum IdentKind { Function, File, Line, Column, SourceLocStruct };
 
-  SourceLocExpr(const ASTContext &Ctx, IdentKind Type, SourceLocation BLoc,
-                SourceLocation RParenLoc, DeclContext *Context);
+  SourceLocExpr(const ASTContext &Ctx, IdentKind Type, QualType ResultTy,
+                SourceLocation BLoc, SourceLocation RParenLoc,
+                DeclContext *Context);
 
   /// Build an empty call expression.
   explicit SourceLocExpr(EmptyShell Empty) : Expr(SourceLocExprClass, Empty) {}
 
   /// Return the result of evaluating this SourceLocExpr in the specified
   /// (and possibly null) default argument or initialization context.
   APValue EvaluateInContext(const ASTContext &Ctx,
                             const Expr *DefaultExpr) const;
 
   /// Return a string representing the name of the specific builtin function.
   StringRef getBuiltinStr() const;
 
   IdentKind getIdentKind() const {
     return static_cast<IdentKind>(SourceLocExprBits.Kind);
   }
 
-  bool isStringType() const {
+  bool isIntType() const {
     switch (getIdentKind()) {
     case File:
     case Function:
-      return true;
+    case SourceLocStruct:
+      return false;
     case Line:
     case Column:
-      return false;
+      return true;
     }
     llvm_unreachable("unknown source location expression kind");
   }
-  bool isIntType() const LLVM_READONLY { return !isStringType(); }
 
   /// If the SourceLocExpr has been resolved return the subexpression
   /// representing the resolved value. Otherwise return null.
   const DeclContext *getParentContext() const { return ParentContext; }
   DeclContext *getParentContext() { return ParentContext; }
 
   SourceLocation getLocation() const { return BuiltinLoc; }
   SourceLocation getBeginLoc() const { return BuiltinLoc; }

clang/include/clang/AST/RecursiveASTVisitor.h

 DEF_TRAVERSE_DECL(BindingDecl, {
   if (getDerived().shouldVisitImplicitCode())
     TRY_TO(TraverseStmt(D->getBinding()));
 })
 
 DEF_TRAVERSE_DECL(MSPropertyDecl, { TRY_TO(TraverseDeclaratorHelper(D)); })
 
 DEF_TRAVERSE_DECL(MSGuidDecl, {})
+DEF_TRAVERSE_DECL(UnnamedGlobalConstantDecl, {})
 
 DEF_TRAVERSE_DECL(TemplateParamObjectDecl, {})
 
 DEF_TRAVERSE_DECL(FieldDecl, {
   TRY_TO(TraverseDeclaratorHelper(D));
   if (D->isBitField())
     TRY_TO(TraverseStmt(D->getBitWidth()));
   else if (D->hasInClassInitializer())

clang/include/clang/AST/Stmt.h

protected:
   class SourceLocExprBitfields {
     friend class ASTStmtReader;
     friend class SourceLocExpr;
 
     unsigned : NumExprBits;
 
     /// The kind of source location builtin represented by the SourceLocExpr.
     /// Ex. __builtin_LINE, __builtin_FUNCTION, ect.
-    unsigned Kind : 2;
+    unsigned Kind : 3;
   };
 
   class StmtExprBitfields {
     friend class ASTStmtReader;
     friend class StmtExpr;
 
     unsigned : NumExprBits;
 

clang/include/clang/Basic/DeclNodes.td

def Named : DeclNode<Decl, "named declarations", 1>;
   def Value : DeclNode<Named, "value declarations", 1>;
     def EnumConstant : DeclNode<Value, "enumerators">;
     def UnresolvedUsingValue : DeclNode<Value>;
     def IndirectField : DeclNode<Value>;
     def Binding : DeclNode<Value>;
     def OMPDeclareReduction : DeclNode<Value>, DeclContext;
     def OMPDeclareMapper : DeclNode<Value>, DeclContext;
     def MSGuid : DeclNode<Value>;
+    def UnnamedGlobalConstant : DeclNode<Value>;
     def TemplateParamObject : DeclNode<Value>;
     def Declarator : DeclNode<Value, "declarators", 1>;
       def Field : DeclNode<Declarator, "non-static data members">;
         def ObjCIvar : DeclNode<Field>;
         def ObjCAtDefsField : DeclNode<Field>;
       def MSProperty : DeclNode<Declarator>;
       def Function : DeclNode<Declarator, "functions">, DeclContext;
         def CXXDeductionGuide : DeclNode<Function>;

clang/include/clang/Basic/DiagnosticSemaKinds.td

def warn_tcb_enforcement_violation : Warning<
   "calling %0 is a violation of trusted computing base '%1'">,
   InGroup<DiagGroup<"tcb-enforcement">>;
 
 // RISC-V builtin required extension warning
 def err_riscv_builtin_requires_extension : Error<
   "builtin requires at least one of the following extensions support to be enabled : %0">;
 def err_riscv_builtin_invalid_lmul : Error<
   "LMUL argument must be in the range [0,3] or [5,7]">;
+
+def err_std_source_location_impl_not_found : Error<
+  "'std::source_location::__impl' was not found; it must be defined before '__builtin_source_location' is called">;
+def err_std_source_location_impl_malformed : Error<
+  "'std::source_location::__impl' must be standard-layout and have only two 'const char *' fields '_M_file_name' and '_M_function_name', and two integral fields '_M_line' and '_M_column'">;
 } // end of sema component.

clang/include/clang/Basic/TokenKinds.def

 UNARY_EXPR_OR_TYPE_TRAIT(__alignof, PreferredAlignOf, KEYALL)
 KEYWORD(__attribute                 , KEYALL)
 KEYWORD(__builtin_choose_expr       , KEYALL)
 KEYWORD(__builtin_offsetof          , KEYALL)
 KEYWORD(__builtin_FILE              , KEYALL)
 KEYWORD(__builtin_FUNCTION          , KEYALL)
 KEYWORD(__builtin_LINE              , KEYALL)
 KEYWORD(__builtin_COLUMN            , KEYALL)
+KEYWORD(__builtin_source_location   , KEYCXX)
 
 // __builtin_types_compatible_p is a GNU C extension that we handle like a C++
 // type trait.
 TYPE_TRAIT_2(__builtin_types_compatible_p, TypeCompatible, KEYNOCXX)
 KEYWORD(__builtin_va_arg            , KEYALL)
 KEYWORD(__extension__               , KEYALL)
 KEYWORD(__float128                  , KEYALL)
 KEYWORD(__ibm128                    , KEYALL)

clang/include/clang/Sema/Sema.h

public:
   NamespaceDecl *CoroTraitsNamespaceCache;
 
   /// The C++ "type_info" declaration, which is defined in \<typeinfo>.
   RecordDecl *CXXTypeInfoDecl;
 
   /// The MSVC "_GUID" struct, which is defined in MSVC header files.
   RecordDecl *MSVCGuidDecl;
 
+  /// The C++ "std::source_location::__impl" struct, defined in
+  /// \<source_location>.
+  RecordDecl *StdSourceLocationImplDecl;
+
   /// Caches identifiers/selectors for NSFoundation APIs.
   std::unique_ptr<NSAPI> NSAPIObj;
 
   /// The declaration of the Objective-C NSNumber class.
   ObjCInterfaceDecl *NSNumberDecl;
 
   /// The declaration of the Objective-C NSValue class.
   ObjCInterfaceDecl *NSValueDecl;
public:
 
   // __builtin_va_arg(expr, type)
   ExprResult ActOnVAArg(SourceLocation BuiltinLoc, Expr *E, ParsedType Ty,
                         SourceLocation RPLoc);
   ExprResult BuildVAArgExpr(SourceLocation BuiltinLoc, Expr *E,
                             TypeSourceInfo *TInfo, SourceLocation RPLoc);
 
   // __builtin_LINE(), __builtin_FUNCTION(), __builtin_FILE(),
-  // __builtin_COLUMN()
+  // __builtin_COLUMN(), __builtin_source_location()
   ExprResult ActOnSourceLocExpr(SourceLocExpr::IdentKind Kind,
                                 SourceLocation BuiltinLoc,
                                 SourceLocation RPLoc);
 
   // Build a potentially resolved SourceLocExpr.
   ExprResult BuildSourceLocExpr(SourceLocExpr::IdentKind Kind,
-                                SourceLocation BuiltinLoc, SourceLocation RPLoc,
+                                QualType ResultTy, SourceLocation BuiltinLoc,
+                                SourceLocation RPLoc,
                                 DeclContext *ParentContext);
 
   // __null
   ExprResult ActOnGNUNullExpr(SourceLocation TokenLoc);
 
   bool CheckCaseExpression(Expr *E);
 
   /// Describes the result of an "if-exists" condition check.

clang/include/clang/Serialization/ASTBitCodes.h

 /// Whenever the AST file format changes in a way that makes it
 /// incompatible with previous versions (such that a reader
 /// designed for the previous version could not support reading
 /// the new version), this number should be increased.
 ///
 /// Version 4 of AST files also requires that the version control branch and
 /// revision match exactly, since there is no backward compatibility of
 /// AST files at this time.
-const unsigned VERSION_MAJOR = 16;
+const unsigned VERSION_MAJOR = 17;
 
 /// AST file minor version number supported by this version of
 /// Clang.
 ///
 /// Whenever the AST format changes in a way that is still
 /// compatible with previous versions (such that a reader designed
 /// for the previous version could still support reading the new
 /// version by ignoring new kinds of subblocks), this number
enum DeclCode {
   DECL_PRAGMA_DETECT_MISMATCH,
 
   /// An OMPDeclareMapperDecl record.
   DECL_OMP_DECLARE_MAPPER,
 
   /// An OMPDeclareReductionDecl record.
   DECL_OMP_DECLARE_REDUCTION,
 
-  DECL_LAST = DECL_OMP_DECLARE_REDUCTION
+  /// A UnnamedGlobalConstantDecl record.
+  DECL_UNNAMED_GLOBAL_CONSTANT,
+
+  DECL_LAST = DECL_UNNAMED_GLOBAL_CONSTANT
 };
 
 /// Record codes for each kind of statement or expression.
 ///
 /// These constants describe the records that describe statements
 /// or expressions. These records  occur within type and declarations
 /// block, so they begin with record values of 128.  Each constant
 /// describes a record for a specific statement or expression class in the

clang/lib/AST/ASTContext.cpp

if (MSGuidDecl *Existing = MSGuidDecls.FindNodeOrInsertPos(ID, InsertPos))
     return Existing;
 
   QualType GUIDType = getMSGuidType().withConst();
   MSGuidDecl *New = MSGuidDecl::Create(*this, GUIDType, Parts);
   MSGuidDecls.InsertNode(New, InsertPos);
   return New;
 }
 
+UnnamedGlobalConstantDecl *
+ASTContext::getUnnamedGlobalConstantDecl(QualType Ty,
+                                         const APValue &APVal) const {
+  llvm::FoldingSetNodeID ID;
+  UnnamedGlobalConstantDecl::Profile(ID, Ty, APVal);
+
+  void *InsertPos;
+  if (UnnamedGlobalConstantDecl *Existing =
+          UnnamedGlobalConstantDecls.FindNodeOrInsertPos(ID, InsertPos))
+    return Existing;
+
+  UnnamedGlobalConstantDecl *New =
+      UnnamedGlobalConstantDecl::Create(*this, Ty, APVal);
+  UnnamedGlobalConstantDecls.InsertNode(New, InsertPos);
+  return New;
+}
+
 TemplateParamObjectDecl *
 ASTContext::getTemplateParamObjectDecl(QualType T, const APValue &V) const {
   assert(T->isRecordType() && "template param object of unexpected type");
 
   // C++ [temp.param]p8:
   //   [...] a static storage duration object of type 'const T' [...]
   T.addConst();
 

clang/lib/AST/ASTImporter.cpp

 ExpectedStmt ASTNodeImporter::VisitExpr(Expr *E) {
   Importer.FromDiag(E->getBeginLoc(), diag::err_unsupported_ast_node)
       << E->getStmtClassName();
   return make_error<ImportError>(ImportError::UnsupportedConstruct);
 }
 
 ExpectedStmt ASTNodeImporter::VisitSourceLocExpr(SourceLocExpr *E) {
   Error Err = Error::success();
+  auto ToType = importChecked(Err, E->getType());
   auto BLoc = importChecked(Err, E->getBeginLoc());
   auto RParenLoc = importChecked(Err, E->getEndLoc());
   if (Err)
     return std::move(Err);
   auto ParentContextOrErr = Importer.ImportContext(E->getParentContext());
   if (!ParentContextOrErr)
     return ParentContextOrErr.takeError();
 
   return new (Importer.getToContext())
-      SourceLocExpr(Importer.getToContext(), E->getIdentKind(), BLoc, RParenLoc,
-                    *ParentContextOrErr);
+      SourceLocExpr(Importer.getToContext(), E->getIdentKind(), ToType, BLoc,
+                    RParenLoc, *ParentContextOrErr);
 }
 
 ExpectedStmt ASTNodeImporter::VisitVAArgExpr(VAArgExpr *E) {
 
   Error Err = Error::success();
   auto ToBuiltinLoc = importChecked(Err, E->getBuiltinLoc());
   auto ToSubExpr = importChecked(Err, E->getSubExpr());
   auto ToWrittenTypeInfo = importChecked(Err, E->getWrittenTypeInfo());

clang/lib/AST/DeclBase.cpp

switch (DeclKind) {
     case PragmaComment:
     case PragmaDetectMismatch:
     case Block:
     case Captured:
     case TranslationUnit:
     case ExternCContext:
     case Decomposition:
     case MSGuid:
+    case UnnamedGlobalConstant:
     case TemplateParamObject:
 
     case UsingDirective:
     case BuiltinTemplate:
     case ClassTemplateSpecialization:
     case ClassTemplatePartialSpecialization:
     case ClassScopeFunctionSpecialization:
     case VarTemplateSpecialization:

clang/lib/AST/DeclCXX.cpp

if (APVal.isAbsent() && isValidStructGUID(getASTContext(), getType())) {
     // Register this APValue to be destroyed if necessary. (Note that the
     // MSGuidDecl destructor is never run.)
     getASTContext().addDestruction(&APVal);
   }
 
   return APVal;
 }
 
+void UnnamedGlobalConstantDecl::anchor() {}
+
+UnnamedGlobalConstantDecl::UnnamedGlobalConstantDecl(DeclContext *DC,
+                                                     QualType Ty,
+                                                     const APValue &Value)
+    : ValueDecl(Decl::UnnamedGlobalConstant, DC, SourceLocation(),
+                DeclarationName(), Ty),
+      Value(Value) {}
+
+UnnamedGlobalConstantDecl *
+UnnamedGlobalConstantDecl::Create(const ASTContext &C, QualType T,
+                                  const APValue &Value) {
+  DeclContext *DC = C.getTranslationUnitDecl();
+  return new (C, DC) UnnamedGlobalConstantDecl(DC, T, Value);
+}
+
+UnnamedGlobalConstantDecl *
+UnnamedGlobalConstantDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
+  return new (C, ID) UnnamedGlobalConstantDecl(nullptr, QualType(), APValue());
+}
+
+void UnnamedGlobalConstantDecl::printName(llvm::raw_ostream &OS) const {
+  OS << "unnamed-global-constant";
+}
+
 static const char *getAccessName(AccessSpecifier AS) {
   switch (AS) {
     case AS_none:
       llvm_unreachable("Invalid access specifier!");
     case AS_public:
       return "public";
     case AS_private:
       return "private";

clang/lib/AST/Expr.cpp

bool BinaryOperator::isNullPointerArithmeticExtension(ASTContext &Ctx,
   // Check that the pointee type is char-sized.
   const PointerType *PTy = PExp->getType()->getAs<PointerType>();
   if (!PTy || !PTy->getPointeeType()->isCharType())
     return false;
 
   return true;
 }
 
-static QualType getDecayedSourceLocExprType(const ASTContext &Ctx,
-                                            SourceLocExpr::IdentKind Kind) {
-  switch (Kind) {
-  case SourceLocExpr::File:
-  case SourceLocExpr::Function: {
-    QualType ArrTy = Ctx.getStringLiteralArrayType(Ctx.CharTy, 0);
-    return Ctx.getPointerType(ArrTy->getAsArrayTypeUnsafe()->getElementType());
-  }
-  case SourceLocExpr::Line:
-  case SourceLocExpr::Column:
-    return Ctx.UnsignedIntTy;
-  }
-  llvm_unreachable("unhandled case");
-}
-
 SourceLocExpr::SourceLocExpr(const ASTContext &Ctx, IdentKind Kind,
-                             SourceLocation BLoc, SourceLocation RParenLoc,
+                             QualType ResultTy, SourceLocation BLoc,
+                             SourceLocation RParenLoc,
                              DeclContext *ParentContext)
-    : Expr(SourceLocExprClass, getDecayedSourceLocExprType(Ctx, Kind),
-           VK_PRValue, OK_Ordinary),
+    : Expr(SourceLocExprClass, ResultTy, VK_PRValue, OK_Ordinary),
       BuiltinLoc(BLoc), RParenLoc(RParenLoc), ParentContext(ParentContext) {
   SourceLocExprBits.Kind = Kind;
   setDependence(ExprDependence::None);
 }
 
 StringRef SourceLocExpr::getBuiltinStr() const {
   switch (getIdentKind()) {
   case File:
     return "__builtin_FILE";
   case Function:
     return "__builtin_FUNCTION";
   case Line:
     return "__builtin_LINE";
   case Column:
     return "__builtin_COLUMN";
+  case SourceLocStruct:
+    return "__builtin_source_location";
   }
   llvm_unreachable("unexpected IdentKind!");
 }
 
 APValue SourceLocExpr::EvaluateInContext(const ASTContext &Ctx,
                                          const Expr *DefaultExpr) const {
   SourceLocation Loc;
   const DeclContext *Context;
APValue SourceLocExpr::EvaluateInContext(const ASTContext &Ctx,
 
   switch (getIdentKind()) {
   case SourceLocExpr::File: {
     SmallString<256> Path(PLoc.getFilename());
     Ctx.getLangOpts().remapPathPrefix(Path);
     return MakeStringLiteral(Path);
   }
   case SourceLocExpr::Function: {
-    const Decl *CurDecl = dyn_cast_or_null<Decl>(Context);
+    const auto *CurDecl = dyn_cast<Decl>(Context);
     return MakeStringLiteral(
         CurDecl ? PredefinedExpr::ComputeName(PredefinedExpr::Function, CurDecl)
                 : std::string(""));
   }
   case SourceLocExpr::Line:
   case SourceLocExpr::Column: {
     llvm::APSInt IntVal(Ctx.getIntWidth(Ctx.UnsignedIntTy),
                         /*isUnsigned=*/true);
     IntVal = getIdentKind() == SourceLocExpr::Line ? PLoc.getLine()
                                                    : PLoc.getColumn();
     return APValue(IntVal);
   }
+  case SourceLocExpr::SourceLocStruct: {
+    // Fill in a std::source_location::__impl structure, by creating an
+    // artificial file-scoped CompoundLiteralExpr, and returning a pointer to
+    // that.
+    const CXXRecordDecl *ImplDecl = getType()->getPointeeCXXRecordDecl();
+    assert(ImplDecl);
+
+    // Construct an APValue for the __impl struct, and get or create a Decl
+    // corresponding to that. Note that we've already verified that the shape of
+    // the ImplDecl type is as expected.
+
+    APValue Value(APValue::UninitStruct(), 0, 4);
+    for (FieldDecl *F : ImplDecl->fields()) {
+      StringRef Name = F->getName();
+      if (Name == "_M_file_name") {
+        SmallString<256> Path(PLoc.getFilename());
+        Ctx.getLangOpts().remapPathPrefix(Path);
+        Value.getStructField(F->getFieldIndex()) = MakeStringLiteral(Path);
+      } else if (Name == "_M_function_name") {
+        // Note: this emits the PrettyFunction name -- different than what
+        // __builtin_FUNCTION() above returns!
+        const auto *CurDecl = dyn_cast<Decl>(Context);
+        Value.getStructField(F->getFieldIndex()) = MakeStringLiteral(
+            CurDecl && !isa<TranslationUnitDecl>(CurDecl)
+                ? StringRef(PredefinedExpr::ComputeName(
+                      PredefinedExpr::PrettyFunction, CurDecl))
+                : "");
+      } else if (Name == "_M_line") {
+        QualType Ty = F->getType();
+        llvm::APSInt IntVal(Ctx.getIntWidth(Ty),
+                            Ty->hasUnsignedIntegerRepresentation());
+        IntVal = PLoc.getLine();
+        Value.getStructField(F->getFieldIndex()) = APValue(IntVal);
+      } else if (Name == "_M_column") {
+        QualType Ty = F->getType();
+        llvm::APSInt IntVal(Ctx.getIntWidth(Ty),
+                            Ty->hasUnsignedIntegerRepresentation());
+        IntVal = PLoc.getColumn();
+        Value.getStructField(F->getFieldIndex()) = APValue(IntVal);
+      }
+    }
+
+    UnnamedGlobalConstantDecl *GV =
+        Ctx.getUnnamedGlobalConstantDecl(getType()->getPointeeType(), Value);
+
+    return APValue(GV, CharUnits::Zero(), ArrayRef<APValue::LValuePathEntry>{},
+                   false);
+  }
   }
   llvm_unreachable("unhandled case");
 }
 
 InitListExpr::InitListExpr(const ASTContext &C, SourceLocation lbraceloc,
                            ArrayRef<Expr *> initExprs, SourceLocation rbraceloc)
     : Expr(InitListExprClass, QualType(), VK_PRValue, OK_Ordinary),
       InitExprs(C, initExprs.size()), LBraceLoc(lbraceloc),

clang/lib/AST/ExprClassification.cpp

static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
 
   if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
     return Cl::CL_MemberFunction;
 
   bool islvalue;
   if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
     islvalue = NTTParm->getType()->isReferenceType() ||
                NTTParm->getType()->isRecordType();
   else
-    islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
-               isa<IndirectFieldDecl>(D) ||
-               isa<BindingDecl>(D) ||
-               isa<MSGuidDecl>(D) ||
-               isa<TemplateParamObjectDecl>(D) ||
-               (Ctx.getLangOpts().CPlusPlus &&
-                (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
-                 isa<FunctionTemplateDecl>(D)));
+    islvalue =
+        isa<VarDecl, FieldDecl, IndirectFieldDecl, BindingDecl, MSGuidDecl,
+            UnnamedGlobalConstantDecl, TemplateParamObjectDecl>(D) ||
+         (isa<FunctionDecl, MSPropertyDecl, FunctionTemplateDecl>(D)));
 
   return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
 }
 
 /// ClassifyUnnamed - Return the classification of an expression yielding an
 /// unnamed value of the given type. This applies in particular to function
 /// calls and casts.
 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {

clang/lib/AST/ExprConstant.cpp

static bool IsGlobalLValue(APValue::LValueBase B) {
   if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>()) {
     // ... the address of an object with static storage duration,
     if (const VarDecl *VD = dyn_cast<VarDecl>(D))
       return VD->hasGlobalStorage();
     if (isa<TemplateParamObjectDecl>(D))
       return true;
     // ... the address of a function,
     // ... the address of a GUID [MS extension],
-    return isa<FunctionDecl>(D) || isa<MSGuidDecl>(D);
+    // ... the address of an unnamed global constant
+    return isa<FunctionDecl, MSGuidDecl, UnnamedGlobalConstantDecl>(D);
   }
 
   if (B.is<TypeInfoLValue>() || B.is<DynamicAllocLValue>())
     return true;
 
   const Expr *E = B.get<const Expr*>();
   switch (E->getStmtClass()) {
   default:
     return false;
case Expr::CallExprClass:
     return IsConstantCall(cast<CallExpr>(E));
   // For GCC compatibility, &&label has static storage duration.
   case Expr::AddrLabelExprClass:
     return true;
   // A Block literal expression may be used as the initialization value for
   // Block variables at global or local static scope.
   case Expr::BlockExprClass:
     return !cast<BlockExpr>(E)->getBlockDecl()->hasCaptures();
+  // The APValue generated from a __builtin_source_location will be emitted as a
+  // literal.
+  case Expr::SourceLocExprClass:
+    return true;
   case Expr::ImplicitValueInitExprClass:
     // FIXME:
     // We can never form an lvalue with an implicit value initialization as its
     // base through expression evaluation, so these only appear in one case: the
     // implicit variable declaration we invent when checking whether a constexpr
     // constructor can produce a constant expression. We must assume that such
     // an expression might be a global lvalue.
     return true;
if (auto *GD = dyn_cast<MSGuidDecl>(D)) {
       if (V.isAbsent()) {
         Info.FFDiag(E, diag::note_constexpr_unsupported_layout)
             << GD->getType();
         return CompleteObject();
       }
       return CompleteObject(LVal.Base, &V, GD->getType());
     }
 
+    // Allow reading the APValue from an UnnamedGlobalConstantDecl.
+    if (auto *GCD = dyn_cast<UnnamedGlobalConstantDecl>(D)) {
+      if (isModification(AK)) {
+        Info.FFDiag(E, diag::note_constexpr_modify_global);
+        return CompleteObject();
+      }
+      return CompleteObject(LVal.Base, const_cast<APValue *>(&GCD->getValue()),
+                            GCD->getType());
+    }
+
     // Allow reading from template parameter objects.
     if (auto *TPO = dyn_cast<TemplateParamObjectDecl>(D)) {
       if (isModification(AK)) {
         Info.FFDiag(E, diag::note_constexpr_modify_global);
         return CompleteObject();
       }
       return CompleteObject(LVal.Base, const_cast<APValue *>(&TPO->getValue()),
                             TPO->getType());
static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info,
   assert(!E->isValueDependent());
   assert(E->isGLValue() || E->getType()->isFunctionType() ||
          E->getType()->isVoidType() || isa<ObjCSelectorExpr>(E));
   return LValueExprEvaluator(Info, Result, InvalidBaseOK).Visit(E);
 }
 
 bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
   const NamedDecl *D = E->getDecl();
-  if (isa<FunctionDecl, MSGuidDecl, TemplateParamObjectDecl>(D))
+  if (isa<FunctionDecl, MSGuidDecl, TemplateParamObjectDecl,
+          UnnamedGlobalConstantDecl>(D))
     return Success(cast<ValueDecl>(D));
   if (const VarDecl *VD = dyn_cast<VarDecl>(D))
     return VisitVarDecl(E, VD);
   if (const BindingDecl *BD = dyn_cast<BindingDecl>(D))
     return Visit(BD->getBinding());
   return Error(E);
 }
 
if (isLambdaCallOperator(Info.CurrentCall->Callee)) {
       }
     }
     return true;
   }
 
   bool VisitCXXNewExpr(const CXXNewExpr *E);
 
   bool VisitSourceLocExpr(const SourceLocExpr *E) {
-    assert(E->isStringType() && "SourceLocExpr isn't a pointer type?");
+    assert(!E->isIntType() && "SourceLocExpr isn't a pointer type?");
     APValue LValResult = E->EvaluateInContext(
         Info.Ctx, Info.CurrentCall->CurSourceLocExprScope.getDefaultExpr());
     Result.setFrom(Info.Ctx, LValResult);
     return true;
   }
 
   bool VisitSYCLUniqueStableNameExpr(const SYCLUniqueStableNameExpr *E) {
     std::string ResultStr = E->ComputeName(Info.Ctx);
bool PointerExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
   QualType Pointee = PExp->getType()->castAs<PointerType>()->getPointeeType();
   return HandleLValueArrayAdjustment(Info, E, Result, Pointee, Offset);
 }
 
 bool PointerExprEvaluator::VisitUnaryAddrOf(const UnaryOperator *E) {
   return evaluateLValue(E->getSubExpr(), Result);
 }
 
+// Is the provided decl 'std::source_location::current'?
+static bool IsDeclSourceLocationCurrent(const FunctionDecl *FD) {
+  if (!FD)
+    return false;
+  const IdentifierInfo *FnII = FD->getIdentifier();
+  if (!FnII || !FnII->isStr("current"))
+    return false;
+
+  const auto *RD = dyn_cast<RecordDecl>(FD->getParent());
+  if (!RD)
+    return false;
+
+  const IdentifierInfo *ClassII = RD->getIdentifier();
+  return RD->isInStdNamespace() && ClassII && ClassII->isStr("source_location");
+}
+
 bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
   const Expr *SubExpr = E->getSubExpr();
 
   switch (E->getCastKind()) {
   default:
     break;
   case CK_BitCast:
   case CK_CPointerToObjCPointerCast:
   case CK_BlockPointerToObjCPointerCast:
   case CK_AnyPointerToBlockPointerCast:
   case CK_AddressSpaceConversion:
     if (!Visit(SubExpr))
       return false;
     // Bitcasts to cv void* are static_casts, not reinterpret_casts, so are
     // permitted in constant expressions in C++11. Bitcasts from cv void* are
     // also static_casts, but we disallow them as a resolution to DR1312.
     if (!E->getType()->isVoidPointerType()) {
-      if (!Result.InvalidBase && !Result.Designator.Invalid &&
+      // In some circumstances, we permit casting from void* to cv1 T*, when the
+      // actual pointee object is actually a cv2 T.
+      bool VoidPtrCastMaybeOK =
+          !Result.InvalidBase && !Result.Designator.Invalid &&
           !Result.IsNullPtr &&
           Info.Ctx.hasSameUnqualifiedType(Result.Designator.getType(Info.Ctx),
-                                          E->getType()->getPointeeType()) &&
-          Info.getStdAllocatorCaller("allocate")) {
-        // Inside a call to std::allocator::allocate and friends, we permit
-        // casting from void* back to cv1 T* for a pointer that points to a
-        // cv2 T.
+                                          E->getType()->getPointeeType());
+      // 1. We'll allow it in std::allocator::allocate, and anything which that
+      //    calls.
+      // 2. We'll allow it in the body of std::source_location:current.  This is
+      //    necessary for libstdc++'s <source_location>, which gave its
+      //    parameter the type void*, and cast from that back to `const __impl*`
+      //    in the body. (Fixed for new versions in gcc.gnu.org/PR104602).
+      if (VoidPtrCastMaybeOK &&
+          (Info.getStdAllocatorCaller("allocate") ||
+           IsDeclSourceLocationCurrent(Info.CurrentCall->Callee))) {
+        // Permitted.
       } else {
         Result.Designator.setInvalid();
         if (SubExpr->getType()->isVoidPointerType())
           CCEDiag(E, diag::note_constexpr_invalid_cast)
             << 3 << SubExpr->getType();
         else
           CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
       }

clang/lib/CodeGen/CGDecl.cpp

if (CGDebugInfo *DI = getDebugInfo())
         DI->EmitAndRetainType(getContext().getEnumType(cast<EnumDecl>(&D)));
     return;
   case Decl::Function:     // void X();
   case Decl::EnumConstant: // enum ? { X = ? }
   case Decl::StaticAssert: // static_assert(X, ""); [C++0x]
   case Decl::Label:        // __label__ x;
   case Decl::Import:
   case Decl::MSGuid:    // __declspec(uuid("..."))
+  case Decl::UnnamedGlobalConstant:
   case Decl::TemplateParamObject:
   case Decl::OMPThreadPrivate:
   case Decl::OMPAllocate:
   case Decl::OMPCapturedExpr:
   case Decl::OMPRequires:
   case Decl::Empty:
   case Decl::Concept:
   case Decl::LifetimeExtendedTemporary:

clang/lib/CodeGen/CGExprConstant.cpp

if (auto VD = dyn_cast<VarDecl>(D)) {
               *VD, CGM.getLLVMLinkageVarDefinition(VD, /*IsConstant=*/false));
         }
       }
     }
 
     if (auto *GD = dyn_cast<MSGuidDecl>(D))
       return CGM.GetAddrOfMSGuidDecl(GD);
 
+    if (auto *GCD = dyn_cast<UnnamedGlobalConstantDecl>(D))
+      return CGM.GetAddrOfUnnamedGlobalConstantDecl(GCD);
+
     if (auto *TPO = dyn_cast<TemplateParamObjectDecl>(D))
       return CGM.GetAddrOfTemplateParamObject(TPO);
 
     return nullptr;
   }
 
   // Handle typeid(T).
   if (TypeInfoLValue TI = base.dyn_cast<TypeInfoLValue>()) {

clang/lib/CodeGen/CodeGenModule.h

private:
   llvm::StringMap<llvm::Constant*> AnnotationStrings;
 
   /// Used for uniquing of annotation arguments.
   llvm::DenseMap<unsigned, llvm::Constant *> AnnotationArgs;
 
   llvm::StringMap<llvm::GlobalVariable *> CFConstantStringMap;
 
   llvm::DenseMap<llvm::Constant *, llvm::GlobalVariable *> ConstantStringMap;
+  llvm::DenseMap<const UnnamedGlobalConstantDecl *, llvm::GlobalVariable *>
+      UnnamedGlobalConstantDeclMap;
   llvm::DenseMap<const Decl*, llvm::Constant *> StaticLocalDeclMap;
   llvm::DenseMap<const Decl*, llvm::GlobalVariable*> StaticLocalDeclGuardMap;
   llvm::DenseMap<const Expr*, llvm::Constant *> MaterializedGlobalTemporaryMap;
 
   llvm::DenseMap<QualType, llvm::Constant *> AtomicSetterHelperFnMap;
   llvm::DenseMap<QualType, llvm::Constant *> AtomicGetterHelperFnMap;
 
   /// Map used to get unique type descriptor constants for sanitizers.
public:
   llvm::Constant *GetFunctionStart(const ValueDecl *Decl);
 
   /// Get the address of the RTTI descriptor for the given type.
   llvm::Constant *GetAddrOfRTTIDescriptor(QualType Ty, bool ForEH = false);
 
   /// Get the address of a GUID.
   ConstantAddress GetAddrOfMSGuidDecl(const MSGuidDecl *GD);
 
+  /// Get the address of a UnnamedGlobalConstant
+  ConstantAddress
+  GetAddrOfUnnamedGlobalConstantDecl(const UnnamedGlobalConstantDecl *GCD);
+
   /// Get the address of a template parameter object.
   ConstantAddress
   GetAddrOfTemplateParamObject(const TemplateParamObjectDecl *TPO);
 
   /// Get the address of the thunk for the given global decl.
   llvm::Constant *GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
                                  GlobalDecl GD);
 

clang/lib/CodeGen/CodeGenModule.cpp

ConstantAddress CodeGenModule::GetAddrOfMSGuidDecl(const MSGuidDecl *GD) {
   }
 
   llvm::Type *Ty = getTypes().ConvertTypeForMem(GD->getType());
   llvm::Constant *Addr = llvm::ConstantExpr::getBitCast(
       GV, Ty->getPointerTo(GV->getAddressSpace()));
   return ConstantAddress(Addr, Ty, Alignment);
 }
 
+ConstantAddress CodeGenModule::GetAddrOfUnnamedGlobalConstantDecl(
+    const UnnamedGlobalConstantDecl *GCD) {
+  CharUnits Alignment = getContext().getTypeAlignInChars(GCD->getType());
+
+  llvm::GlobalVariable **Entry = nullptr;
+  Entry = &UnnamedGlobalConstantDeclMap[GCD];
+  if (*Entry)
+    return ConstantAddress(*Entry, (*Entry)->getValueType(), Alignment);
+
+  ConstantEmitter Emitter(*this);
+  llvm::Constant *Init;
+
+  const APValue &V = GCD->getValue();
+
+  assert(!V.isAbsent());
+  Init = Emitter.emitForInitializer(V, GCD->getType().getAddressSpace(),
+                                    GCD->getType());
+
+  auto *GV = new llvm::GlobalVariable(getModule(), Init->getType(),
+                                      /*isConstant=*/true,
+                                      llvm::GlobalValue::PrivateLinkage, Init,
+                                      ".constant");
+  GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
+  GV->setAlignment(Alignment.getAsAlign());
+
+  Emitter.finalize(GV);
+
+  *Entry = GV;
+  return ConstantAddress(GV, GV->getValueType(), Alignment);
+}
+
 ConstantAddress CodeGenModule::GetAddrOfTemplateParamObject(
     const TemplateParamObjectDecl *TPO) {
   StringRef Name = getMangledName(TPO);
   CharUnits Alignment = getNaturalTypeAlignment(TPO->getType());
 
   if (llvm::GlobalVariable *GV = getModule().getNamedGlobal(Name))
     return ConstantAddress(GV, GV->getValueType(), Alignment);
 

clang/lib/Parse/ParseExpr.cpp

 /// [GNU]   '__builtin_va_arg' '(' assignment-expression ',' type-name ')'
 /// [GNU]   '__builtin_offsetof' '(' type-name ',' offsetof-member-designator')'
 /// [GNU]   '__builtin_choose_expr' '(' assign-expr ',' assign-expr ','
 ///                                     assign-expr ')'
 /// [GNU]   '__builtin_FILE' '(' ')'
 /// [GNU]   '__builtin_FUNCTION' '(' ')'
 /// [GNU]   '__builtin_LINE' '(' ')'
 /// [CLANG] '__builtin_COLUMN' '(' ')'
+/// [GNU]   '__builtin_source_location' '(' ')'
 /// [GNU]   '__builtin_types_compatible_p' '(' type-name ',' type-name ')'
 /// [GNU]   '__null'
 /// [OBJC]  '[' objc-message-expr ']'
 /// [OBJC]  '\@selector' '(' objc-selector-arg ')'
 /// [OBJC]  '\@protocol' '(' identifier ')'
 /// [OBJC]  '\@encode' '(' type-name ')'
 /// [OBJC]  objc-string-literal
 /// [C++]   simple-type-specifier '(' expression-list[opt] ')'      [C++ 5.2.3]
#undef RTT_JOIN
   case tok::kw___builtin_offsetof:
   case tok::kw___builtin_choose_expr:
   case tok::kw___builtin_astype: // primary-expression: [OCL] as_type()
   case tok::kw___builtin_convertvector:
   case tok::kw___builtin_COLUMN:
   case tok::kw___builtin_FILE:
   case tok::kw___builtin_FUNCTION:
   case tok::kw___builtin_LINE:
+  case tok::kw___builtin_source_location:
     if (NotPrimaryExpression)
       *NotPrimaryExpression = true;
     // This parses the complete suffix; we can return early.
     return ParseBuiltinPrimaryExpression();
   case tok::kw___null:
     Res = Actions.ActOnGNUNullExpr(ConsumeToken());
     break;
 

 /// [GNU]   '__builtin_offsetof' '(' type-name ',' offsetof-member-designator')'
 /// [GNU]   '__builtin_choose_expr' '(' assign-expr ',' assign-expr ','
 ///                                     assign-expr ')'
 /// [GNU]   '__builtin_types_compatible_p' '(' type-name ',' type-name ')'
 /// [GNU]   '__builtin_FILE' '(' ')'
 /// [GNU]   '__builtin_FUNCTION' '(' ')'
 /// [GNU]   '__builtin_LINE' '(' ')'
 /// [CLANG] '__builtin_COLUMN' '(' ')'
+/// [GNU]   '__builtin_source_location' '(' ')'
 /// [OCL]   '__builtin_astype' '(' assignment-expression ',' type-name ')'
 ///
 /// [GNU] offsetof-member-designator:
 /// [GNU]   identifier
 /// [GNU]   offsetof-member-designator '.' identifier
 /// [GNU]   offsetof-member-designator '[' expression ']'
 /// \endverbatim
 ExprResult Parser::ParseBuiltinPrimaryExpression() {
case tok::kw___builtin_convertvector: {
 
     Res = Actions.ActOnConvertVectorExpr(Expr.get(), DestTy.get(), StartLoc,
                                          ConsumeParen());
     break;
   }
   case tok::kw___builtin_COLUMN:
   case tok::kw___builtin_FILE:
   case tok::kw___builtin_FUNCTION:
-  case tok::kw___builtin_LINE: {
+  case tok::kw___builtin_LINE:
+  case tok::kw___builtin_source_location: {
     // Attempt to consume the r-paren.
     if (Tok.isNot(tok::r_paren)) {
       Diag(Tok, diag::err_expected) << tok::r_paren;
       SkipUntil(tok::r_paren, StopAtSemi);
       return ExprError();
     }
     SourceLocExpr::IdentKind Kind = [&] {
       switch (T) {
       case tok::kw___builtin_FILE:
         return SourceLocExpr::File;
       case tok::kw___builtin_FUNCTION:
         return SourceLocExpr::Function;
       case tok::kw___builtin_LINE:
         return SourceLocExpr::Line;
       case tok::kw___builtin_COLUMN:
         return SourceLocExpr::Column;
+      case tok::kw___builtin_source_location:
+        return SourceLocExpr::SourceLocStruct;
       default:
         llvm_unreachable("invalid keyword");
       }
     }();
     Res = Actions.ActOnSourceLocExpr(Kind, StartLoc, ConsumeParen());
     break;
   }
   }

clang/lib/Sema/Sema.cpp

: ExternalSource(nullptr), isMultiplexExternalSource(false),
       DataSegStack(nullptr), BSSSegStack(nullptr), ConstSegStack(nullptr),
       CodeSegStack(nullptr), FpPragmaStack(FPOptionsOverride()),
       CurInitSeg(nullptr), VisContext(nullptr),
       PragmaAttributeCurrentTargetDecl(nullptr),
       IsBuildingRecoveryCallExpr(false), LateTemplateParser(nullptr),
       LateTemplateParserCleanup(nullptr), OpaqueParser(nullptr), IdResolver(pp),
       StdExperimentalNamespaceCache(nullptr), StdInitializerList(nullptr),
       StdCoroutineTraitsCache(nullptr), CXXTypeInfoDecl(nullptr),
-      MSVCGuidDecl(nullptr), NSNumberDecl(nullptr), NSValueDecl(nullptr),
-      NSStringDecl(nullptr), StringWithUTF8StringMethod(nullptr),
+      MSVCGuidDecl(nullptr), StdSourceLocationImplDecl(nullptr),
+      NSNumberDecl(nullptr), NSValueDecl(nullptr), NSStringDecl(nullptr),
+      StringWithUTF8StringMethod(nullptr),
       ValueWithBytesObjCTypeMethod(nullptr), NSArrayDecl(nullptr),
       ArrayWithObjectsMethod(nullptr), NSDictionaryDecl(nullptr),
       DictionaryWithObjectsMethod(nullptr), GlobalNewDeleteDeclared(false),
       TUKind(TUKind), NumSFINAEErrors(0),
       FullyCheckedComparisonCategories(
           static_cast<unsigned>(ComparisonCategoryType::Last) + 1),
       SatisfactionCache(Context), AccessCheckingSFINAE(false),
       InNonInstantiationSFINAEContext(false), NonInstantiationEntries(0),

clang/lib/Sema/SemaExpr.cpp

 #define DECL(type, base) case Decl::type:
 #include "clang/AST/DeclNodes.inc"
     llvm_unreachable("invalid value decl kind");
 
   // These shouldn't make it here.
   case Decl::ObjCAtDefsField:
     llvm_unreachable("forming non-member reference to ivar?");
 
   // Enum constants are always r-values and never references.
   // Unresolved using declarations are dependent.
   case Decl::EnumConstant:
   case Decl::UnresolvedUsingValue:
   case Decl::OMPDeclareReduction:
   case Decl::OMPDeclareMapper:
     valueKind = VK_PRValue;
     break;
 
#include "clang/AST/DeclNodes.inc"
   case Decl::MSProperty:
   case Decl::MSGuid:
   case Decl::TemplateParamObject:
     // FIXME: Should MSGuidDecl and template parameter objects be subject to
     // capture in OpenMP, or duplicated between host and device?
     valueKind = VK_LValue;
     break;
 
+  case Decl::UnnamedGlobalConstant:
+    valueKind = VK_LValue;
+    break;
+
   case Decl::CXXMethod:
     // If we're referring to a method with an __unknown_anytype
     // result type, make the entire expression __unknown_anytype.
     // This should only be possible with a type written directly.
     if (const FunctionProtoType *proto =
             dyn_cast<FunctionProtoType>(VD->getType()))
       if (proto->getReturnType() == Context.UnknownAnyTy) {
         type = Context.UnknownAnyTy;
if (const VarDecl *vd = dyn_cast<VarDecl>(dcl)) {
           QualType MPTy = Context.getMemberPointerType(
               op->getType(),
               Context.getTypeDeclType(cast<RecordDecl>(Ctx)).getTypePtr());
           // Under the MS ABI, lock down the inheritance model now.
           if (Context.getTargetInfo().getCXXABI().isMicrosoft())
             (void)isCompleteType(OpLoc, MPTy);
           return MPTy;
         }
       }
-    } else if (!isa<FunctionDecl>(dcl) && !isa<NonTypeTemplateParmDecl>(dcl) &&
-               !isa<BindingDecl>(dcl) && !isa<MSGuidDecl>(dcl))
+    } else if (!isa<FunctionDecl, NonTypeTemplateParmDecl, BindingDecl,
+                    MSGuidDecl, UnnamedGlobalConstantDecl>(dcl))
       llvm_unreachable("Unknown/unexpected decl type");
   }
 
   if (AddressOfError != AO_No_Error) {
     diagnoseAddressOfInvalidType(*this, OpLoc, op, AddressOfError);
     return QualType();
   }
 
   if (lval == Expr::LV_IncompleteVoidType) {
else if (pw == Context.getTargetInfo().getLongLongWidth())
     Ty = Context.LongLongTy;
   else {
     llvm_unreachable("I don't know size of pointer!");
   }
 
   return new (Context) GNUNullExpr(Ty, TokenLoc);
 }
 
+static CXXRecordDecl *LookupStdSourceLocationImpl(Sema &S, SourceLocation Loc) {
+  CXXRecordDecl *ImplDecl = nullptr;
+
+  // Fetch the std::source_location::__impl decl.
+  if (NamespaceDecl *Std = S.getStdNamespace()) {
+    LookupResult ResultSL(S, &S.PP.getIdentifierTable().get("source_location"),
+                          Loc, Sema::LookupOrdinaryName);
+    if (S.LookupQualifiedName(ResultSL, Std)) {
+      if (auto *SLDecl = ResultSL.getAsSingle<RecordDecl>()) {
+        LookupResult ResultImpl(S, &S.PP.getIdentifierTable().get("__impl"),
+                                Loc, Sema::LookupOrdinaryName);
+        if ((SLDecl->isCompleteDefinition() || SLDecl->isBeingDefined()) &&
+            S.LookupQualifiedName(ResultImpl, SLDecl)) {
+          ImplDecl = ResultImpl.getAsSingle<CXXRecordDecl>();
+        }
+      }
+    }
+  }
+
+  if (!ImplDecl || !ImplDecl->isCompleteDefinition()) {
+    S.Diag(Loc, diag::err_std_source_location_impl_not_found);
+    return nullptr;
+  }
+
+  // Verify that __impl is a trivial struct type, with no base classes, and with
+  // only the four expected fields.
+  if (ImplDecl->isUnion() || !ImplDecl->isStandardLayout() ||
+      ImplDecl->getNumBases() != 0) {
+    S.Diag(Loc, diag::err_std_source_location_impl_malformed);
+    return nullptr;
+  }
+
+  unsigned Count = 0;
+  for (FieldDecl *F : ImplDecl->fields()) {
+    StringRef Name = F->getName();
+
+    if (Name == "_M_file_name") {
+      if (F->getType() !=
+          S.Context.getPointerType(S.Context.CharTy.withConst()))
+        break;
+      Count++;
+    } else if (Name == "_M_function_name") {
+      if (F->getType() !=
+          S.Context.getPointerType(S.Context.CharTy.withConst()))
+        break;
+      Count++;
+    } else if (Name == "_M_line") {
+      if (!F->getType()->isIntegerType())
+        break;
+      Count++;
+    } else if (Name == "_M_column") {
+      if (!F->getType()->isIntegerType())
+        break;
+      Count++;
+    } else {
+      Count = 100; // invalid
+      break;
+    }
+  }
+  if (Count != 4) {
+    S.Diag(Loc, diag::err_std_source_location_impl_malformed);
+    return nullptr;
+  }
+
+  return ImplDecl;
+}
+
 ExprResult Sema::ActOnSourceLocExpr(SourceLocExpr::IdentKind Kind,
                                     SourceLocation BuiltinLoc,
                                     SourceLocation RPLoc) {
-  return BuildSourceLocExpr(Kind, BuiltinLoc, RPLoc, CurContext);
+  QualType ResultTy;
+  switch (Kind) {
+  case SourceLocExpr::File:
+  case SourceLocExpr::Function: {
+    QualType ArrTy = Context.getStringLiteralArrayType(Context.CharTy, 0);
+    ResultTy =
+        Context.getPointerType(ArrTy->getAsArrayTypeUnsafe()->getElementType());
+    break;
+  }
+  case SourceLocExpr::Line:
+  case SourceLocExpr::Column:
+    ResultTy = Context.UnsignedIntTy;
+    break;
+  case SourceLocExpr::SourceLocStruct:
+    if (!StdSourceLocationImplDecl) {
+      StdSourceLocationImplDecl =
+          LookupStdSourceLocationImpl(*this, BuiltinLoc);
+      if (!StdSourceLocationImplDecl)
+        return ExprError();
+    }
+    ResultTy = Context.getPointerType(
+        Context.getRecordType(StdSourceLocationImplDecl).withConst());
+    break;
+  }
+
+  return BuildSourceLocExpr(Kind, ResultTy, BuiltinLoc, RPLoc, CurContext);
 }
 
 ExprResult Sema::BuildSourceLocExpr(SourceLocExpr::IdentKind Kind,
+                                    QualType ResultTy,
                                     SourceLocation BuiltinLoc,
                                     SourceLocation RPLoc,
                                     DeclContext *ParentContext) {
   return new (Context)
-      SourceLocExpr(Context, Kind, BuiltinLoc, RPLoc, ParentContext);
+      SourceLocExpr(Context, Kind, ResultTy, BuiltinLoc, RPLoc, ParentContext);
 }
 
 bool Sema::CheckConversionToObjCLiteral(QualType DstType, Expr *&Exp,
                                         bool Diagnose) {
   if (!getLangOpts().ObjC)
     return false;
 
   const ObjCObjectPointerType *PT = DstType->getAs<ObjCObjectPointerType>();

clang/lib/Sema/SemaTemplate.cpp

case APValue::LValue: {
       assert(ParamType->isPointerType() || ParamType->isReferenceType() ||
              ParamType->isNullPtrType());
       // -- a temporary object
       // -- a string literal
       // -- the result of a typeid expression, or
       // -- a predefined __func__ variable
       APValue::LValueBase Base = Value.getLValueBase();
       auto *VD = const_cast<ValueDecl *>(Base.dyn_cast<const ValueDecl *>());
-      if (Base && (!VD || isa<LifetimeExtendedTemporaryDecl>(VD))) {
+      if (Base &&
+          (!VD ||
+           isa<LifetimeExtendedTemporaryDecl, UnnamedGlobalConstantDecl>(VD))) {
         Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
             << Arg->getSourceRange();
         return ExprError();
       }
       // -- a subobject
       // FIXME: Until C++20
       if (Value.hasLValuePath() && Value.getLValuePath().size() == 1 &&
           VD && VD->getType()->isArrayType() &&
           Value.getLValuePath()[0].getAsArrayIndex() == 0 &&

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

 TemplateDeclInstantiator::VisitExternCContextDecl(ExternCContextDecl *D) {
   llvm_unreachable("extern \"C\" context cannot be instantiated");
 }
 
 Decl *TemplateDeclInstantiator::VisitMSGuidDecl(MSGuidDecl *D) {
   llvm_unreachable("GUID declaration cannot be instantiated");
 }
 
+Decl *TemplateDeclInstantiator::VisitUnnamedGlobalConstantDecl(
+    UnnamedGlobalConstantDecl *D) {
+  llvm_unreachable("UnnamedGlobalConstantDecl cannot be instantiated");
+}
+
 Decl *TemplateDeclInstantiator::VisitTemplateParamObjectDecl(
     TemplateParamObjectDecl *D) {
   llvm_unreachable("template parameter objects cannot be instantiated");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitLabelDecl(LabelDecl *D) {
   LabelDecl *Inst = LabelDecl::Create(SemaRef.Context, Owner, D->getLocation(),

clang/lib/Sema/TreeTransform.h

   }
 
   /// Build a new expression representing a call to a source location
   ///  builtin.
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide different behavior.
   ExprResult RebuildSourceLocExpr(SourceLocExpr::IdentKind Kind,
-                                  SourceLocation BuiltinLoc,
+                                  QualType ResultTy, SourceLocation BuiltinLoc,
                                   SourceLocation RPLoc,
                                   DeclContext *ParentContext) {
-    return getSema().BuildSourceLocExpr(Kind, BuiltinLoc, RPLoc, ParentContext);
+    return getSema().BuildSourceLocExpr(Kind, ResultTy, BuiltinLoc, RPLoc,
+                                        ParentContext);
   }
 
   /// Build a new Objective-C boxed expression.
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide different behavior.
   ExprResult RebuildConceptSpecializationExpr(NestedNameSpecifierLoc NNS,
       SourceLocation TemplateKWLoc, DeclarationNameInfo ConceptNameInfo,

 template <typename Derived>
 ExprResult TreeTransform<Derived>::TransformSourceLocExpr(SourceLocExpr *E) {
   bool NeedRebuildFunc = E->getIdentKind() == SourceLocExpr::Function &&
                          getSema().CurContext != E->getParentContext();
 
   if (!getDerived().AlwaysRebuild() && !NeedRebuildFunc)
     return E;
 
-  return getDerived().RebuildSourceLocExpr(E->getIdentKind(), E->getBeginLoc(),
-                                           E->getEndLoc(),
+  return getDerived().RebuildSourceLocExpr(E->getIdentKind(), E->getType(),
+                                           E->getBeginLoc(), E->getEndLoc(),
                                            getSema().CurContext);
 }
 
 template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformCUDAKernelCallExpr(CUDAKernelCallExpr *E) {
   // Transform the callee.
   ExprResult Callee = getDerived().TransformExpr(E->getCallee());

clang/lib/Serialization/ASTCommon.cpp

bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::UnresolvedUsingTypename:
   case Decl::TemplateTypeParm:
   case Decl::EnumConstant:
   case Decl::UnresolvedUsingValue:
   case Decl::IndirectField:
   case Decl::Field:
   case Decl::MSProperty:
   case Decl::MSGuid:
+  case Decl::UnnamedGlobalConstant:
   case Decl::TemplateParamObject:
   case Decl::ObjCIvar:
   case Decl::ObjCAtDefsField:
   case Decl::NonTypeTemplateParm:
   case Decl::TemplateTemplateParm:
   case Decl::Using:
   case Decl::UsingEnum:
   case Decl::UsingPack:

clang/lib/Serialization/ASTReaderDecl.cpp

public:
     void VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *GD);
     void VisitCXXMethodDecl(CXXMethodDecl *D);
     void VisitCXXConstructorDecl(CXXConstructorDecl *D);
     void VisitCXXDestructorDecl(CXXDestructorDecl *D);
     void VisitCXXConversionDecl(CXXConversionDecl *D);
     void VisitFieldDecl(FieldDecl *FD);
     void VisitMSPropertyDecl(MSPropertyDecl *FD);
     void VisitMSGuidDecl(MSGuidDecl *D);
+    void VisitUnnamedGlobalConstantDecl(UnnamedGlobalConstantDecl *D);
     void VisitTemplateParamObjectDecl(TemplateParamObjectDecl *D);
     void VisitIndirectFieldDecl(IndirectFieldDecl *FD);
     RedeclarableResult VisitVarDeclImpl(VarDecl *D);
     void VisitVarDecl(VarDecl *VD) { VisitVarDeclImpl(VD); }
     void VisitImplicitParamDecl(ImplicitParamDecl *PD);
     void VisitParmVarDecl(ParmVarDecl *PD);
     void VisitDecompositionDecl(DecompositionDecl *DD);
     void VisitBindingDecl(BindingDecl *BD);
void ASTDeclReader::VisitMSGuidDecl(MSGuidDecl *D) {
   for (auto &C : D->PartVal.Part4And5)
     C = Record.readInt();
 
   // Add this GUID to the AST context's lookup structure, and merge if needed.
   if (MSGuidDecl *Existing = Reader.getContext().MSGuidDecls.GetOrInsertNode(D))
     Reader.getContext().setPrimaryMergedDecl(D, Existing->getCanonicalDecl());
 }
 
+void ASTDeclReader::VisitUnnamedGlobalConstantDecl(
+    UnnamedGlobalConstantDecl *D) {
+  VisitValueDecl(D);
+  D->Value = Record.readAPValue();
+
+  // Add this to the AST context's lookup structure, and merge if needed.
+  if (UnnamedGlobalConstantDecl *Existing =
+          Reader.getContext().UnnamedGlobalConstantDecls.GetOrInsertNode(D))
+    Reader.getContext().setPrimaryMergedDecl(D, Existing->getCanonicalDecl());
+}
+
 void ASTDeclReader::VisitTemplateParamObjectDecl(TemplateParamObjectDecl *D) {
   VisitValueDecl(D);
   D->Value = Record.readAPValue();
 
   // Add this template parameter object to the AST context's lookup structure,
   // and merge if needed.
   if (TemplateParamObjectDecl *Existing =
           Reader.getContext().TemplateParamObjectDecls.GetOrInsertNode(D))
case DECL_BLOCK:
     D = BlockDecl::CreateDeserialized(Context, ID);
     break;
   case DECL_MS_PROPERTY:
     D = MSPropertyDecl::CreateDeserialized(Context, ID);
     break;
   case DECL_MS_GUID:
     D = MSGuidDecl::CreateDeserialized(Context, ID);
     break;
+  case DECL_UNNAMED_GLOBAL_CONSTANT:
+    D = UnnamedGlobalConstantDecl::CreateDeserialized(Context, ID);
+    break;
   case DECL_TEMPLATE_PARAM_OBJECT:
     D = TemplateParamObjectDecl::CreateDeserialized(Context, ID);
     break;
   case DECL_CAPTURED:
     D = CapturedDecl::CreateDeserialized(Context, ID, Record.readInt());
     break;
   case DECL_CXX_BASE_SPECIFIERS:
     Error("attempt to read a C++ base-specifier record as a declaration");

clang/lib/Serialization/ASTWriterDecl.cpp

public:
     void VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *D);
     void VisitCXXMethodDecl(CXXMethodDecl *D);
     void VisitCXXConstructorDecl(CXXConstructorDecl *D);
     void VisitCXXDestructorDecl(CXXDestructorDecl *D);
     void VisitCXXConversionDecl(CXXConversionDecl *D);
     void VisitFieldDecl(FieldDecl *D);
     void VisitMSPropertyDecl(MSPropertyDecl *D);
     void VisitMSGuidDecl(MSGuidDecl *D);
+    void VisitUnnamedGlobalConstantDecl(UnnamedGlobalConstantDecl *D);
     void VisitTemplateParamObjectDecl(TemplateParamObjectDecl *D);
     void VisitIndirectFieldDecl(IndirectFieldDecl *D);
     void VisitVarDecl(VarDecl *D);
     void VisitImplicitParamDecl(ImplicitParamDecl *D);
     void VisitParmVarDecl(ParmVarDecl *D);
     void VisitDecompositionDecl(DecompositionDecl *D);
     void VisitBindingDecl(BindingDecl *D);
     void VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);
void ASTDeclWriter::VisitMSGuidDecl(MSGuidDecl *D) {
   MSGuidDecl::Parts Parts = D->getParts();
   Record.push_back(Parts.Part1);
   Record.push_back(Parts.Part2);
   Record.push_back(Parts.Part3);
   Record.append(std::begin(Parts.Part4And5), std::end(Parts.Part4And5));
   Code = serialization::DECL_MS_GUID;
 }
 
+void ASTDeclWriter::VisitUnnamedGlobalConstantDecl(
+    UnnamedGlobalConstantDecl *D) {
+  VisitValueDecl(D);
+  Record.AddAPValue(D->getValue());
+  Code = serialization::DECL_UNNAMED_GLOBAL_CONSTANT;
+}
+
 void ASTDeclWriter::VisitTemplateParamObjectDecl(TemplateParamObjectDecl *D) {
   VisitValueDecl(D);
   Record.AddAPValue(D->getValue());
   Code = serialization::DECL_TEMPLATE_PARAM_OBJECT;
 }
 
 void ASTDeclWriter::VisitIndirectFieldDecl(IndirectFieldDecl *D) {
   VisitValueDecl(D);

clang/test/CodeGenCXX/builtin-source-location.cpp

 // RUN: %clang_cc1 -std=c++2a -fblocks %s -triple x86_64-unknown-unknown -emit-llvm -o %t.ll
 
 // This needs to be performed before #line directives which alter filename
 // RUN: %clang_cc1 -fmacro-prefix-map=%p=/UNLIKELY/PATH -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-PREFIX-MAP
 //
 // CHECK-PREFIX-MAP: /UNLIKELY/PATH{{/|\\\\}}builtin-source-location.cpp
 void testRemap() {
   const char *file = __builtin_FILE();
 }
 
 #line 8 "builtin-source-location.cpp"
 
-struct source_location {
-private:
-  unsigned int __m_line = 0;
-  unsigned int __m_col = 0;
-  const char *__m_file = nullptr;
-  const char *__m_func = nullptr;
-
+namespace std {
+class source_location {
 public:
-  constexpr void set(unsigned l, unsigned c, const char *f, const char *func) {
-    __m_line = l;
-    __m_col = c;
-    __m_file = f;
-    __m_func = func;
-  }
-  static constexpr source_location current(
-      unsigned int __line = __builtin_LINE(),
-      unsigned int __col = __builtin_COLUMN(),
-      const char *__file = __builtin_FILE(),
-      const char *__func = __builtin_FUNCTION()) noexcept {
+  static constexpr source_location current(const void *__p = __builtin_source_location()) noexcept {
     source_location __loc;
-    __loc.set(__line, __col, __file, __func);
+    __loc.__m_impl = static_cast<const __impl *>(__p);
     return __loc;
   }
-  static source_location bad_current(
-      unsigned int __line = __builtin_LINE(),
-      unsigned int __col = __builtin_COLUMN(),
-      const char *__file = __builtin_FILE(),
-      const char *__func = __builtin_FUNCTION()) noexcept {
-    source_location __loc;
-    __loc.set(__line, __col, __file, __func);
-    return __loc;
+  static source_location bad_current(const void *__p = __builtin_source_location()) noexcept {
+    return current(__p);
   }
   constexpr source_location() = default;
   constexpr source_location(source_location const &) = default;
-  constexpr unsigned int line() const noexcept { return __m_line; }
-  constexpr unsigned int column() const noexcept { return __m_col; }
-  constexpr const char *file() const noexcept { return __m_file; }
-  constexpr const char *function() const noexcept { return __m_func; }
+  constexpr unsigned int line() const noexcept { return __m_impl->_M_line; }
+  constexpr unsigned int column() const noexcept { return __m_impl->_M_column; }
+  constexpr const char *file() const noexcept { return __m_impl->_M_file_name; }
+  constexpr const char *function() const noexcept { return __m_impl->_M_function_name; }
+
+private:
+  // Note: The type name "std::source_location::__impl", and its constituent
+  // field-names are required by __builtin_source_location().
+  struct __impl {
+    const char *_M_file_name;
+    const char *_M_function_name;
+    unsigned _M_line;
+    unsigned _M_column;
+  };
+  const __impl *__m_impl = nullptr;
 };
+} // namespace std
 
-using SL = source_location;
+using SL = std::source_location;
 
 extern "C" int sink(...);
 
-
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-GLOBAL-ONE
 //
 // CHECK-GLOBAL-ONE-DAG: @[[FILE:.*]] = {{.*}}c"test_const_init.cpp\00"
 // CHECK-GLOBAL-ONE-DAG: @[[FUNC:.*]] = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
-//
-// CHECK-GLOBAL-ONE: @const_init_global ={{.*}} global %struct.source_location { i32 1000, i32 {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]]
+// CHECK-GLOBAL-ONE-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 1000, i32 {{[0-9]+}} }, align 8
+// CHECK-GLOBAL-ONE: @const_init_global ={{.*}} global %"class.std::source_location" { %"struct.std::source_location::__impl"* @[[IMPL]] }, align 8
 #line 1000 "test_const_init.cpp"
 SL const_init_global = SL::current();
 
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-GLOBAL-TWO
 //
-// CHECK-GLOBAL-TWO-DAG: @runtime_init_global ={{.*}} global %struct.source_location zeroinitializer, align 8
+// CHECK-GLOBAL-TWO-DAG: @runtime_init_global ={{.*}} global %"class.std::source_location" zeroinitializer, align 8
 //
 // CHECK-GLOBAL-TWO-DAG: @[[FILE:.*]] = {{.*}}c"test_runtime_init.cpp\00"
 // CHECK-GLOBAL-TWO-DAG: @[[FUNC:.*]] = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+// CHECK-GLOBAL-TWO-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 1100, i32 {{[0-9]+}} }, align 8
 //
 // CHECK-GLOBAL-TWO: define internal void @__cxx_global_var_init()
 // CHECK-GLOBAL-TWO-NOT: ret
-// CHECK-GLOBAL-TWO: call void @_ZN15source_location11bad_currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 @runtime_init_global,
-// CHECK-GLOBAL-TWO-SAME: i32 noundef 1100, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]],
+// CHECK-GLOBAL-TWO: %call = call %"struct.std::source_location::__impl"* @_ZNSt15source_location11bad_currentEPKv({{.*}} @[[IMPL]]
+// CHECK-GLOBAL-TWO: store %"struct.std::source_location::__impl"* %call, {{.*}} @runtime_init_global
+
 #line 1100 "test_runtime_init.cpp"
 SL runtime_init_global = SL::bad_current();
 
 #line 2000 "test_function.cpp"
 extern "C" void test_function() {
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-LOCAL-ONE
 //
 // CHECK-LOCAL-ONE-DAG: @[[FILE:.*]] = {{.*}}c"test_current.cpp\00"
-// CHECK-LOCAL-ONE-DAG: @[[FUNC:.*]] = {{.*}}c"test_function\00"
+// CHECK-LOCAL-ONE-DAG: @[[FUNC:.*]] = {{.*}}c"void test_function()\00"
+// CHECK-LOCAL-ONE-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 2100, i32 {{[0-9]+}} }, align 8
 //
-// CHECK-LOCAL-ONE:  call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %local,
-// CHECK-LOCAL-ONE-SAME: i32 noundef 2100, i32 noundef {{[0-9]+}},
-// CHECK-LOCAL-ONE-SAME: {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]],
+// CHECK-LOCAL-ONE:  define {{.*}} @test_function
+// CHECK-LOCAL-ONE:  call %"struct.std::source_location::__impl"* @_ZNSt15source_location7currentEPKv({{.*}} @[[IMPL]]
 #line 2100 "test_current.cpp"
   SL local = SL::current();
 }
 
 #line 3000 "TestInitClass.cpp"
 struct TestInit {
   SL info = SL::current();
   SL arg_info;
 
 #line 3100 "TestInitCtor.cpp"
   TestInit(SL arg_info = SL::current()) : arg_info(arg_info) {}
 };
 
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-CTOR-GLOBAL
 //
 // CHECK-CTOR-GLOBAL-DAG: @GlobalInitVal ={{.*}} global %struct.TestInit zeroinitializer, align 8
 // CHECK-CTOR-GLOBAL-DAG: @[[FILE:.*]] = {{.*}}c"GlobalInitVal.cpp\00"
 // CHECK-CTOR-GLOBAL-DAG: @[[FUNC:.*]] = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+// CHECK-CTOR-GLOBAL-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 3400, i32 {{[0-9]+}} }, align 8
 //
 // CHECK-CTOR-GLOBAL: define internal void @__cxx_global_var_init.{{[0-9]+}}()
 // CHECK-CTOR-GLOBAL-NOT: ret
 //
-// CHECK-CTOR-GLOBAL: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[TMP_ONE:[^,]*]],
-// CHECK-CTOR-GLOBAL-SAME: i32 noundef 3400, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]],
-// CHECK-CTOR-GLOBAL-NEXT: call void @_ZN8TestInitC1E15source_location(%struct.TestInit* {{[^,]*}} @GlobalInitVal, %struct.source_location* {{.*}}%[[TMP_ONE]])
+// CHECK-CTOR-GLOBAL: call %"struct.std::source_location::__impl"* @_ZNSt15source_location7currentEPKv({{.*}} @[[IMPL]]
+// CHECK-CTOR-GLOBAL-NOT: ret
+// CHECK-CTOR-GLOBAL: call void @_ZN8TestInitC1ESt15source_location(%struct.TestInit* {{[^,]*}} @GlobalInitVal, %"struct.std::source_location::__impl"*
 #line 3400 "GlobalInitVal.cpp"
 TestInit GlobalInitVal;
 
 extern "C" void test_init_function() {
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-CTOR-LOCAL
 //
 // CHECK-CTOR-LOCAL-DAG: @[[FILE:.*]] = {{.*}}c"LocalInitVal.cpp\00"
-// CHECK-CTOR-LOCAL-DAG: @[[FUNC:.*]] = {{.*}}c"test_init_function\00"
+// CHECK-CTOR-LOCAL-DAG: @[[FUNC:.*]] = {{.*}}c"void test_init_function()\00"
+// CHECK-CTOR-LOCAL-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 3500, i32 {{[0-9]+}} }, align 8
 //
 // CHECK-CTOR-LOCAL: define{{.*}} void @test_init_function()
 // CHECK-CTOR-LOCAL-NOT: ret
 //
-// CHECK-CTOR-LOCAL: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[TMP:[^,]*]],
-// CHECK-CTOR-LOCAL-SAME: i32 noundef 3500, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]],
-// CHECK-CTOR-LOCAL-NEXT: call void @_ZN8TestInitC1E15source_location(%struct.TestInit* {{[^,]*}} %init_local, %struct.source_location* {{.*}}%[[TMP]])
+// CHECK-CTOR-LOCAL: call %"struct.std::source_location::__impl"* @_ZNSt15source_location7currentEPKv({{.*}} @[[IMPL]]
+// CHECK-CTOR-LOCAL-NOT: ret
+// CHECK-CTOR-LOCAL: call void @_ZN8TestInitC1ESt15source_location(%struct.TestInit* {{[^,]*}} %init_local, %"struct.std::source_location::__impl"*
+
 #line 3500 "LocalInitVal.cpp"
   TestInit init_local;
   sink(init_local);
 }
 
 #line 4000 "ConstexprClass.cpp"
 struct TestInitConstexpr {
   SL info = SL::current();
   SL arg_info;
 #line 4200 "ConstexprCtor.cpp"
   constexpr TestInitConstexpr(SL arg_info = SL::current()) : arg_info(arg_info) {}
 };
 
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-CONSTEXPR-T2
 //
 // CHECK-CONSTEXPR-T2-DAG: @[[FILE_INIT:.*]] = {{.*}}c"ConstexprCtor.cpp\00"
-// CHECK-CONSTEXPR-T2-DAG: @[[FUNC_INIT:.*]] = {{.*}}c"TestInitConstexpr\00"
+// CHECK-CONSTEXPR-T2-DAG: @[[FUNC_INIT:.*]] = {{.*}}c"TestInitConstexpr::TestInitConstexpr(SL)\00"
+// CHECK-CONSTEXPR-T2-DAG: @[[IMPL_INIT:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE_INIT]], {{[^@]*}}@[[FUNC_INIT]], {{.*}} i32 4200, i32 {{[0-9]+}} }, align 8
 // CHECK-CONSTEXPR-T2-DAG: @[[FILE_ARG:.*]] = {{.*}}c"ConstexprGlobal.cpp\00"
 // CHECK-CONSTEXPR-T2-DAG: @[[EMPTY:.*]] = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+// CHECK-CONSTEXPR-T2-DAG: @[[IMPL_ARG:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE_ARG]], {{[^@]*}}@[[EMPTY]], {{.*}} i32 4400, i32 {{[0-9]+}} }, align 8
 //
 // CHECK-CONSTEXPR-T2: @ConstexprGlobal ={{.*}} global %struct.TestInitConstexpr {
-// CHECK-CONSTEXPR-T2-SAME: %struct.source_location { i32 4200, i32 {{[0-9]+}}, {{[^@]*}}@[[FILE_INIT]], {{[^@]*}}@[[FUNC_INIT]],
-// CHECK-CONSTEXPR-T2-SAME: {{[^%]*}}%struct.source_location { i32 4400, i32 {{[0-9]+}},  {{[^@]*}}@[[FILE_ARG]], {{[^@]*}}@[[EMPTY]]
+// CHECK-CONSTEXPR-T2-SAME: %"class.std::source_location" { %"struct.std::source_location::__impl"* @[[IMPL_INIT]] },
+// CHECK-CONSTEXPR-T2-SAME: %"class.std::source_location" { %"struct.std::source_location::__impl"* @[[IMPL_ARG]] }
 #line 4400 "ConstexprGlobal.cpp"
 TestInitConstexpr ConstexprGlobal;
 
 extern "C" void test_init_function_constexpr() {
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-CONSTEXPR-LOCAL
 //
-// CHECK-CONSTEXPR-LOCAL-DAG: @[[FUNC:.*]] = {{.*}}c"test_init_function_constexpr\00"
+// CHECK-CONSTEXPR-LOCAL-DAG: @[[FUNC:.*]] = {{.*}}c"void test_init_function_constexpr()\00"
 // CHECK-CONSTEXPR-LOCAL-DAG: @[[FILE:.*]] = {{.*}}c"ConstexprLocal.cpp\00"
+// CHECK-CONSTEXPR-LOCAL-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 4600, i32 {{[0-9]+}} }, align 8
 //
 // CHECK-CONSTEXPR-LOCAL: define{{.*}} void @test_init_function_constexpr()
-// CHECK-CONSTEXPR-LOCAL: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[TMP:[^,]*]],
-// CHECK-CONSTEXPR-LOCAL-SAME: i32 noundef 4600, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]]
-// CHECK-CONSTEXPR-LOCAL: call void @_ZN17TestInitConstexprC1E15source_location(%struct.TestInitConstexpr* {{[^,]*}} %local_val, {{.*}}%[[TMP]])
+// CHECK-CONSTEXPR-LOCAL-NOT: ret
+// CHECK-CONSTEXPR-LOCAL: call %"struct.std::source_location::__impl"* @_ZNSt15source_location7currentEPKv({{.*}} @[[IMPL]]
+// CHECK-CONSTEXPR-LOCAL-NOT: ret
+// CHECK-CONSTEXPR-LOCAL: call void @_ZN17TestInitConstexprC1ESt15source_location(%struct.TestInitConstexpr* {{[^,]*}} %local_val, %"struct.std::source_location::__impl"*
 #line 4600 "ConstexprLocal.cpp"
   TestInitConstexpr local_val;
 }
 
 #line 5000 "TestInitAgg.cpp"
 struct TestInitAgg {
 #line 5100 "i1.cpp"
   SL i1;
 #line 5200 "i2.cpp"
   SL i2 = SL::current();
 #line 5300 "TestInitAggEnd.cpp"
 };
 
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-AGG-DEFAULT
 //
 // CHECK-AGG-DEFAULT-DAG: @[[FILE:.*]] = {{.*}}c"TestInitAgg.cpp\00"
-// CHECK-AGG-DEFAULT-DAG: @[[FUNC:.*]] = {{.*}}c"TestInitAgg\00"
+// CHECK-AGG-DEFAULT-DAG: @[[FUNC:.*]] = {{.*}}c"TestInitAgg::TestInitAgg()\00"
+// CHECK-AGG-DEFAULT-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 5000, i32 {{[0-9]+}} }, align 8
 //
 // CHECK-AGG-DEFAULT: @GlobalAggDefault ={{.*}} global %struct.TestInitAgg {
-// CHECK-AGG-DEFAULT-SAME: %struct.source_location zeroinitializer,
-// CHECK-AGG-DEFAULT-SAME: %struct.source_location { i32 5000, i32 {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]]
+// CHECK-AGG-DEFAULT-SAME: %"class.std::source_location" zeroinitializer,
+// CHECK-AGG-DEFAULT-SAME: %"class.std::source_location" { %"struct.std::source_location::__impl"* @[[IMPL]] }
 #line 5400 "GlobalAggDefault.cpp"
 TestInitAgg GlobalAggDefault;
 
 #line 5500 "test_agg_init_test.cpp"
 extern "C" void test_agg_init() {
-// RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-AGG-BRACE
-//
-// CHECK-AGG-BRACE-DAG: @[[FILE:.*]] = {{.*}}c"BraceInitEnd.cpp\00"
-// CHECK-AGG-BRACE-DAG: @[[FUNC:.*]] = {{.*}}c"test_agg_init\00"
-//
-// CHECK-AGG-BRACE: define{{.*}} void @test_agg_init()
-// CHECK-AGG-BRACE: %[[I2:.*]] = getelementptr inbounds %struct.TestInitAgg, %struct.TestInitAgg* %local_brace_init, i32 0, i32 1
-// CHECK-AGG-BRACE-NEXT: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[I2]],
-// CHECK-AGG-BRACE-SAME: i32 noundef 5700, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]]
+// RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-AGG-INIT
+
+// CHECK-AGG-INIT-DAG: @[[FUNC:.*]] = {{.*}}c"void test_agg_init()\00"
+
+// CHECK-AGG-INIT-DAG: @[[FILE:.*]] = {{.*}}c"BraceInitEnd.cpp\00"
+// CHECK-AGG-INIT-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 5700, i32 {{[0-9]+}} }, align 8
+
 #line 5600 "BraceInitStart.cpp"
   TestInitAgg local_brace_init{
 #line 5700 "BraceInitEnd.cpp"
   };
 
-// RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-AGG-EQUAL
-//
-// CHECK-AGG-EQUAL-DAG: @[[FILE:.*]] = {{.*}}c"EqualInitEnd.cpp\00"
-// CHECK-AGG-EQUAL-DAG: @[[FUNC:.*]] = {{.*}}c"test_agg_init\00"
-//
-// CHECK-AGG-EQUAL: define{{.*}} void @test_agg_init()
-// CHECK-AGG-EQUAL: %[[I2:.*]] = getelementptr inbounds %struct.TestInitAgg, %struct.TestInitAgg* %local_equal_init, i32 0, i32 1
-// CHECK-AGG-EQUAL-NEXT: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[I2]],
-// CHECK-AGG-EQUAL-SAME: i32 noundef 5900, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]]
+// CHECK-AGG-INIT-DAG: @[[FILE:.*]] = {{.*}}c"EqualInitEnd.cpp\00"
+// CHECK-AGG-INIT-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 5900, i32 {{[0-9]+}} }, align 8
+
 #line 5800 "EqualInitStart.cpp"
   TestInitAgg local_equal_init =
       {
 #line 5900 "EqualInitEnd.cpp"
       };
 
-// RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-AGG-LIST
-//
-// CHECK-AGG-LIST-DAG: @[[FILE_DEFAULT:.*]] = {{.*}}c"InitListEnd.cpp\00"
-// CHECK-AGG-LIST-DAG: @[[FILE_ELEM:.*]] = {{.*}}c"ListElem.cpp\00"
-// CHECK-AGG-LIST-DAG: @[[FUNC:.*]] = {{.*}}c"test_agg_init\00"
-//
-// CHECK-AGG-LIST: define{{.*}} void @test_agg_init()
-//
-// CHECK-AGG-LIST: %[[I1:.*]] =  getelementptr inbounds %struct.TestInitAgg, %struct.TestInitAgg* %local_list_init, i32 0, i32 0
-// CHECK-AGG-LIST-NEXT: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[I1]],
-// CHECK-AGG-LIST-SAME: i32 noundef 6100, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE_ELEM]], {{[^@]*}}@[[FUNC]]
-//
-// CHECK-AGG-LIST: %[[I2:.*]] = getelementptr inbounds %struct.TestInitAgg, %struct.TestInitAgg* %local_list_init, i32 0, i32 1
-// CHECK-AGG-LIST-NEXT: call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[I2]],
-// CHECK-AGG-LIST-SAME: i32 noundef 6200, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE_DEFAULT]], {{[^@]*}}@[[FUNC]]
+
+// CHECK-AGG-INIT-DAG: @[[FILE_DEFAULT:.*]] = {{.*}}c"InitListEnd.cpp\00"
+// CHECK-AGG-INIT-DAG: @[[FILE_ELEM:.*]] = {{.*}}c"ListElem.cpp\00"
+// CHECK-AGG-INIT-DAG: @[[IMPL_DEFAULT:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE_ELEM]], {{[^@]*}}@[[FUNC]], {{.*}} i32 6100, i32 {{[0-9]+}} }, align 8
+// CHECK-AGG-INIT-DAG: @[[IMPL_ELEM:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE_DEFAULT]], {{[^@]*}}@[[FUNC]], {{.*}} i32 6200, i32 {{[0-9]+}} }, align 8
+
 #line 6000 "InitListStart.cpp"
   TestInitAgg local_list_init =
       {
 #line 6100 "ListElem.cpp"
           {SL::current()}
 #line 6200 "InitListEnd.cpp"
       };
 }

 #line 7200 "test_template.cpp"
 template <class T, int V>
 void test_template() {
 
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-TEMPL -DINT_ID=0
 // RUN: FileCheck --input-file %t.ll %s --check-prefix=CHECK-TEMPL -DINT_ID=1
 //
 // CHECK-TEMPL-DAG: @[[FILE:.*]] = {{.*}}c"local_templ.cpp\00"
-// CHECK-TEMPL-DAG: @[[FUNC:.*]] = {{.*}}c"test_template\00"
-//
-// CHECK-TEMPL: define weak_odr void @_Z13test_templateI15source_locationLi[[INT_ID]]EEvv()
-// CHECK-TEMPL-NEXT: entry:
-// CHECK-TEMPL-NOT: ret
-//
-// CHECK-TEMPL:  call void @_ZN15source_location7currentEjjPKcS1_(%struct.source_location* sret(%struct.source_location) align 8 %[[TMP:[^,]*]],
-// CHECK-TEMPL-SAME: i32 noundef 7300, i32 noundef {{[0-9]+}}, {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]]
+// CHECK-TEMPL-DAG: @[[FUNC:.*]] = {{.*}}c"void test_template() [T = std::source_location, V = [[INT_ID]]]\00"
+// CHECK-TEMPL-DAG: @[[IMPL:.*]] = private unnamed_addr constant %"struct.std::source_location::__impl" { {{[^@]*}}@[[FILE]], {{[^@]*}}@[[FUNC]], {{.*}} i32 7300, i32 {{[0-9]+}} }, align 8
 #line 7300 "local_templ.cpp"
   TestTemplate<T, V> local_templ;
 }
 #line 7400 "EndTestTemplate.cpp"
 template void test_template<SL, 0>();
 template void test_template<SL, 1>();

clang/test/SemaCXX/source_location.cpp

 // RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify %s
 // expected-no-diagnostics
 
 #define assert(...) ((__VA_ARGS__) ? ((void)0) : throw 42)
 #define CURRENT_FROM_MACRO() SL::current()
 #define FORWARD(...) __VA_ARGS__
 
 template <unsigned>
 struct Printer;
 
 namespace std {
-namespace experimental {
-struct source_location {
-private:
-  unsigned int __m_line = 0;
-  unsigned int __m_col = 0;
-  const char *__m_file = nullptr;
-  const char *__m_func = nullptr;
+class source_location {
+  struct __impl;
+
 public:
-  static constexpr source_location current(
-      const char *__file = __builtin_FILE(),
-      const char *__func = __builtin_FUNCTION(),
-      unsigned int __line = __builtin_LINE(),
-      unsigned int __col = __builtin_COLUMN()) noexcept {
+  static constexpr source_location current(const __impl *__p = __builtin_source_location()) noexcept {
     source_location __loc;
-    __loc.__m_line = __line;
-    __loc.__m_col = __col;
-    __loc.__m_file = __file;
-    __loc.__m_func = __func;
+    __loc.__m_impl = __p;
     return __loc;
   }
   constexpr source_location() = default;
   constexpr source_location(source_location const &) = default;
-  constexpr unsigned int line() const noexcept { return __m_line; }
-  constexpr unsigned int column() const noexcept { return __m_col; }
-  constexpr const char *file() const noexcept { return __m_file; }
-  constexpr const char *function() const noexcept { return __m_func; }
+  constexpr unsigned int line() const noexcept { return __m_impl ? __m_impl->_M_line : 0; }
+  constexpr unsigned int column() const noexcept { return __m_impl ? __m_impl->_M_column : 0; }
+  constexpr const char *file() const noexcept { return __m_impl ? __m_impl->_M_file_name : ""; }
+  constexpr const char *function() const noexcept { return __m_impl ? __m_impl->_M_function_name : ""; }
+
+private:
+  // Note: The type name "std::source_location::__impl", and its constituent
+  // field-names are required by __builtin_source_location().
+  struct __impl {
+    const char *_M_file_name;
+    const char *_M_function_name;
+    unsigned _M_line;
+    unsigned _M_column;
+  };
+  const __impl *__m_impl = nullptr;
+
+public:
+  using public_impl_alias = __impl;
 };
-} // namespace experimental
 } // namespace std
 
-using SL = std::experimental::source_location;
+using SL = std::source_location;
 
 #include "Inputs/source-location-file.h"
 namespace SLF = source_location_file;
 
 constexpr bool is_equal(const char *LHS, const char *RHS) {
   while (*LHS != 0 && *RHS != 0) {
     if (*LHS != *RHS)
       return false;

 template <class T>
 constexpr bool is_same<T, T> = true;
 
 // test types
 static_assert(is_same<decltype(__builtin_LINE()), unsigned>);
 static_assert(is_same<decltype(__builtin_COLUMN()), unsigned>);
 static_assert(is_same<decltype(__builtin_FILE()), const char *>);
 static_assert(is_same<decltype(__builtin_FUNCTION()), const char *>);
+static_assert(is_same<decltype(__builtin_source_location()), const std::source_location::public_impl_alias *>);
 
 // test noexcept
 static_assert(noexcept(__builtin_LINE()));
 static_assert(noexcept(__builtin_COLUMN()));
 static_assert(noexcept(__builtin_FILE()));
 static_assert(noexcept(__builtin_FUNCTION()));
+static_assert(noexcept(__builtin_source_location()));
 
 //===----------------------------------------------------------------------===//
 //                            __builtin_LINE()
 //===----------------------------------------------------------------------===//
 
 namespace test_line {
 static_assert(SL::current().line() == __LINE__);
 static_assert(SL::current().line() == CURRENT_FROM_MACRO().line());

 constexpr bool test_function() {
   return is_equal(__func__, test_func_simple()) &&
          !is_equal(get_function(), test_func_simple());
 }
 static_assert(test_function());
 
 template <class T, class U = SL>
 constexpr Pair<U, U> test_func_template(T, U u = U::current()) {
-  static_assert(is_equal(__func__, U::current().function()));
+  static_assert(is_equal(__PRETTY_FUNCTION__, U::current().function()));
   return {u, U::current()};
 }
 template <class T>
 void func_template_tests() {
   constexpr auto P = test_func_template(42);
   //static_assert(is_equal(P.first.function(), __func__), "");
   //static_assert(!is_equal(P.second.function(), __func__), "");
 }
 template void func_template_tests<int>();
 
 template <class = int, class T = SL>
 struct TestCtor {
   T info = T::current();
   T ctor_info;
   TestCtor() = default;
   template <class U = SL>
   constexpr TestCtor(int, U u = U::current()) : ctor_info(u) {}
 };
 void ctor_tests() {
   constexpr TestCtor<> Default;
   constexpr TestCtor<> Template{42};
-  static_assert(!is_equal(Default.info.function(), __func__));
-  static_assert(is_equal(Default.info.function(), "TestCtor"));
-  static_assert(is_equal(Template.info.function(), "TestCtor"));
-  static_assert(is_equal(Template.ctor_info.function(), __func__));
+  static const char *XYZZY = Template.info.function();
+  static_assert(is_equal(Default.info.function(), "test_func::TestCtor<>::TestCtor() [T = std::source_location]"));
+  static_assert(is_equal(Default.ctor_info.function(), ""));
+  static_assert(is_equal(Template.info.function(), "test_func::TestCtor<>::TestCtor(int, U) [T = std::source_location, U = std::source_location]"));
+  static_assert(is_equal(Template.ctor_info.function(), __PRETTY_FUNCTION__));
 }
 
 constexpr SL global_sl = SL::current();
 static_assert(is_equal(global_sl.function(), ""));
 
 } // namespace test_func
 
 //===----------------------------------------------------------------------===//
 //                            __builtin_COLUMN()
#line 4400 "test_func_passed.cpp"
   static_assert(b.a.n == 4400, "");
   static_assert(b.a.n2 == 4400, "");
   static_assert(b.a.info.line() == 4400, "");
   static_assert(is_equal(b.a.f, "test_func_passed.cpp"));
   static_assert(is_equal(b.a.f2, "test_func_passed.cpp"));
   static_assert(is_equal(b.a.info.file(), "test_func_passed.cpp"));
   static_assert(is_equal(b.a.func, "test_in_func"));
   static_assert(is_equal(b.a.func2, "test_in_func"));
-  static_assert(is_equal(b.a.info.function(), "test_in_func"));
+  static_assert(is_equal(b.a.info.function(), "bool test_out_of_line_init::test_in_func()"));
   return true;
 }
 static_assert(test_in_func());
 
 } // end namespace test_out_of_line_init
 
 namespace test_global_scope {
 #line 5000 "test_global_scope.cpp"

clang/test/SemaCXX/source_location_err.cpp

+// RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify -DTEST=1 %s
+// RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify -DTEST=2 %s
+// RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify -DTEST=3 %s
+// RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify -DTEST=4 %s
+// RUN: %clang_cc1 -std=c++1z -fcxx-exceptions -fexceptions -verify -DTEST=5 %s
+
+#if TEST == 1
+auto test1a = __builtin_source_location(); // expected-error {{'std::source_location::__impl' was not found}}
+
+namespace std {
+inline namespace NS {
+  struct source_location;
+}
+}
+
+auto test1b = __builtin_source_location(); // expected-error {{'std::source_location::__impl' was not found}}
+
+namespace std {
+inline namespace NS {
+  struct source_location {
+    struct __impl;
+  };
+}
+}
+auto test1c = __builtin_source_location(); // expected-error {{'std::source_location::__impl' was not found}}
+
+#elif TEST == 2
+auto test2a = __builtin_source_location(); // expected-error {{'std::source_location::__impl' was not found}}
+
+namespace std {
+inline namespace NS {
+struct source_location {
+  struct __impl { int x; };
+};
+}
+}
+auto test2b = __builtin_source_location(); // expected-error {{'std::source_location::__impl' must be standard-layout and have only two 'const char *' fields '_M_file_name' and '_M_function_name', and two integral fields '_M_line' and '_M_column'}}
+
+#elif TEST == 3
+namespace std {
+struct source_location {
+  struct __impl {
+    int other_member;
+    char _M_line;
+    const char *_M_file_name;
+    char _M_column;
+    const char *_M_function_name;
+  };
+};
+}
+auto test3 = __builtin_source_location(); // expected-error {{'std::source_location::__impl' must be standard-layout and have only two 'const char *' fields '_M_file_name' and '_M_function_name', and two integral fields '_M_line' and '_M_column'}}
+
+#elif TEST == 4
+namespace std {
+struct source_location {
+  struct parent {};
+  struct __impl : public parent {
+    char _M_line;
+    const char *_M_file_name;
+    char _M_column;
+    const char *_M_function_name;
+  };
+};
+}
+auto test4 = __builtin_source_location(); // expected-error {{'std::source_location::__impl' must be standard-layout and have only two 'const char *' fields '_M_file_name' and '_M_function_name', and two integral fields '_M_line' and '_M_column'}}
+
+
+#elif TEST == 5
+namespace std {
+struct source_location {
+  struct __impl {
+    signed char _M_line; // odd integral type to choose, but ok!
+    const char *_M_file_name;
+    signed char _M_column;
+    const char *_M_function_name;
+    static int other_member; // static members are OK
+  };
+  using BuiltinT = decltype(__builtin_source_location()); // OK.
+};
+}
+
+// Verify that the address cannot be used as a non-type template argument.
+template <auto X = __builtin_source_location()>
+auto fn1() {return X;} // expected-note {{candidate template ignored: substitution failure: non-type template argument does not refer to any declaration}}
+auto test5a = fn1<>(); // expected-error {{no matching function for call to 'fn1'}}
+
+// (But using integer subobjects by value is okay.)
+template <auto X = __builtin_source_location()->_M_column>
+auto fn2() {return X;}
+auto test5b = fn2<>();
+
+// While it's not semantically required, for efficiency, we ensure that two
+// source-locations with the same content will point to the same object. Given
+// the odd definition of the struct used here (using 'signed char'), any
+// line-number modulo 256 will thus have the same content, and be deduplicated.
+#line 128
+constexpr auto sl1 = __builtin_source_location();
+#line 384
+constexpr auto sl2 = __builtin_source_location();
+constexpr auto sl3 = __builtin_source_location();
+static_assert(sl1 == sl2);
+static_assert(sl1 != sl3);
+static_assert(sl1->_M_line == -128);
+
+#endif

clang/tools/libclang/CIndex.cpp

CXCursor clang_getCursorDefinition(CXCursor C) {
   case Decl::TypeAlias:
   case Decl::TypeAliasTemplate:
   case Decl::TemplateTypeParm:
   case Decl::EnumConstant:
   case Decl::Field:
   case Decl::Binding:
   case Decl::MSProperty:
   case Decl::MSGuid:
+  case Decl::UnnamedGlobalConstant:
   case Decl::TemplateParamObject:
   case Decl::IndirectField:
   case Decl::ObjCIvar:
   case Decl::ObjCAtDefsField:
   case Decl::ImplicitParam:
   case Decl::ParmVar:
   case Decl::NonTypeTemplateParm:
   case Decl::TemplateTemplateParm: