[llvm] revisions to LLVM_ABI export macro definitions (#144598)

## Purpose

Simplify the logic used to define `LLVM_ABI` and related macros,
eliminate the `LLVM_ABI_FRIEND` macro, and update the `LLVM_ABI` macro
to always resolve to `__attribute__((visibility("default")))` when
building LLVM as a shared library for ELF or Mach-O targets.

## Background

Previously, `LLVM_ABI` was defined to the C++ style attribute
`[[gnu::visibility("default")]]` when compiling with gcc, which has more
restrictions on its placement. Of note, the C++ style attributes cannot
decorate `friend` functions and must not appear after `extern` on
variable declarations.

Documentation for `LLVM_ABI` and related annotations is found in the
LLVM repo
[here](https://github.com/llvm/llvm-project/blob/main/llvm/docs/InterfaceExportAnnotations.rst).

## Overview
- Define a new CMake config value,
`LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS`, which is implicitly set whenever
`LLVM_BUILD_LLVM_DYLIB`, `LLVM_BUILD_SHARED_LIBS`, or
`LLVM_ENABLE_PLUGINS` is set. Add it as a `#cmakedefine` to
llvm-config.h so its definition is available to projects building
against LLVM as required so clients see `__declspec(dllimport)` on
Windows.
- Gate the `LLVM_ABI` macro definitions in Compiler.h behind the new
`LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS` definition. This is
simpler/cleaner, but should be equivalent to the previous logic.
- Maintain `LLVM_BUILD_STATIC` as an override to be used by specific
targets that don't want to build against the DLL/shared library, such as
tablegen.
- For ELF and Mach-O targets, directly define `LLVM_ABI` as
`__attribute__((visibility("default")))` instead of
`LLVM_ATTRIBUTE_VISIBILITY_DEFAULT`, which resolves to C++ style
`[[gnu::visibility("default")]]` when compiling with gcc.
- Remove the `LLVM_ABI_FRIEND` macro and replace all usages of it with
`LLVM_ABI`.
- Update the documentation for exporting friend functions to no longer
reference `LLVM_ABI_FRIEND`.

## Validation
- Built as static lib with clang and gcc on Linux.
- Built as static with clang-cl and MSVC on Windows.
- Built as shared lib with clang and gcc on Linux (+ additional local
changes not yet merged).
- Built as DLL with clang-cl and MSVC on Windows (+ additional local
changes not yet merged).

---------

Co-authored-by: SquallATF <squallatf@gmail.com>

llvm/CMakeLists.txt

@@ -942,6 +942,13 @@ if (LLVM_LINK_LLVM_DYLIB AND BUILD_SHARED_LIBS)
   message(FATAL_ERROR "Cannot enable BUILD_SHARED_LIBS with LLVM_LINK_LLVM_DYLIB.  We recommend disabling BUILD_SHARED_LIBS.")
 endif()
 
+set(LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS OFF)
+if (LLVM_BUILD_LLVM_DYLIB OR LLVM_BUILD_SHARED_LIBS OR LLVM_ENABLE_PLUGINS)
+  # Export annotations for LLVM must be enabled if building as a shared lib or
+  # enabling plugins.
+  set(LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS ON)
+endif()
+
 option(LLVM_OPTIMIZED_TABLEGEN "Force TableGen to be built with optimization" OFF)
 if(CMAKE_CROSSCOMPILING OR (LLVM_OPTIMIZED_TABLEGEN AND (LLVM_ENABLE_ASSERTIONS OR CMAKE_CONFIGURATION_TYPES)))
   set(LLVM_USE_HOST_TOOLS ON)

llvm/docs/InterfaceExportAnnotations.rst

@@ -222,7 +222,7 @@ method in a C++ class, it may be annotated for export.
 Friend Functions
 ~~~~~~~~~~~~~~~~
 Friend functions declared in a class, struct or union must be annotated with
-``LLVM_ABI_FRIEND`` if the corresponding function declaration is annotated with
+``LLVM_ABI`` if the corresponding function declaration is annotated with
 ``LLVM_ABI``. This requirement applies even when the class containing the friend
 declaration is annotated with ``LLVM_ABI``.
 
@@ -236,14 +236,13 @@ declaration is annotated with ``LLVM_ABI``.
    class ExampleClass {
      // Friend declaration of a function must be annotated the same as the actual
      // function declaration.
-     LLVM_ABI_FRIEND friend int friend_function(ExampleClass &obj);
+     LLVM_ABI friend int friend_function(ExampleClass &obj);
    };
 
 .. note::
 
    Annotating the friend declaration avoids an “inconsistent dll linkage”
-   compiler error when building a DLL for Windows. The ``LLVM_ABI_FRIEND``
-   annotation is a no-op when building ELF or Mach-O shared libraries.
+   compiler error when building a DLL for Windows.
 
 Virtual Table and Type Info
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~

llvm/include/llvm/ADT/APFloat.h

@@ -572,7 +572,7 @@ public:
   /// emphasizes producing different codes for different inputs in order to
   /// be used in canonicalization and memoization. As such, equality is
   /// bitwiseIsEqual, and 0 != -0.
-  LLVM_ABI_FRIEND friend hash_code hash_value(const IEEEFloat &Arg);
+  LLVM_ABI friend hash_code hash_value(const IEEEFloat &Arg);
 
   /// Converts this value into a decimal string.
   ///
@@ -629,13 +629,12 @@ public:
   ///   0   -> \c IEK_Zero
   ///   Inf -> \c IEK_Inf
   ///
-  LLVM_ABI_FRIEND friend int ilogb(const IEEEFloat &Arg);
+  LLVM_ABI friend int ilogb(const IEEEFloat &Arg);
 
   /// Returns: X * 2^Exp for integral exponents.
-  LLVM_ABI_FRIEND friend IEEEFloat scalbn(IEEEFloat X, int Exp, roundingMode);
+  LLVM_ABI friend IEEEFloat scalbn(IEEEFloat X, int Exp, roundingMode);
 
-  LLVM_ABI_FRIEND friend IEEEFloat frexp(const IEEEFloat &X, int &Exp,
-                                         roundingMode);
+  LLVM_ABI friend IEEEFloat frexp(const IEEEFloat &X, int &Exp, roundingMode);
 
   /// \name Special value setters.
   /// @{
@@ -906,11 +905,11 @@ public:
   LLVM_ABI LLVM_READONLY int getExactLog2() const;
   LLVM_ABI LLVM_READONLY int getExactLog2Abs() const;
 
-  LLVM_ABI_FRIEND friend DoubleAPFloat scalbn(const DoubleAPFloat &X, int Exp,
+  LLVM_ABI friend DoubleAPFloat scalbn(const DoubleAPFloat &X, int Exp,
                                        roundingMode);
-  LLVM_ABI_FRIEND friend DoubleAPFloat frexp(const DoubleAPFloat &X, int &Exp,
+  LLVM_ABI friend DoubleAPFloat frexp(const DoubleAPFloat &X, int &Exp,
                                       roundingMode);
-  LLVM_ABI_FRIEND friend hash_code hash_value(const DoubleAPFloat &Arg);
+  LLVM_ABI friend hash_code hash_value(const DoubleAPFloat &Arg);
 };
 
 LLVM_ABI hash_code hash_value(const DoubleAPFloat &Arg);
@@ -1518,7 +1517,7 @@ public:
     APFLOAT_DISPATCH_ON_SEMANTICS(getExactLog2());
   }
 
-  LLVM_ABI_FRIEND friend hash_code hash_value(const APFloat &Arg);
+  LLVM_ABI friend hash_code hash_value(const APFloat &Arg);
   friend int ilogb(const APFloat &Arg) { return ilogb(Arg.getIEEE()); }
   friend APFloat scalbn(APFloat X, int Exp, roundingMode RM);
   friend APFloat frexp(const APFloat &X, int &Exp, roundingMode RM);

llvm/include/llvm/ADT/SlowDynamicAPInt.h

@@ -62,18 +62,17 @@ public:
   LLVM_ABI SlowDynamicAPInt &operator++();
   LLVM_ABI SlowDynamicAPInt &operator--();
 
-  LLVM_ABI_FRIEND friend SlowDynamicAPInt abs(const SlowDynamicAPInt &X);
-  LLVM_ABI_FRIEND friend SlowDynamicAPInt ceilDiv(const SlowDynamicAPInt &LHS,
+  LLVM_ABI friend SlowDynamicAPInt abs(const SlowDynamicAPInt &X);
+  LLVM_ABI friend SlowDynamicAPInt ceilDiv(const SlowDynamicAPInt &LHS,
                                            const SlowDynamicAPInt &RHS);
-  LLVM_ABI_FRIEND friend SlowDynamicAPInt floorDiv(const SlowDynamicAPInt &LHS,
+  LLVM_ABI friend SlowDynamicAPInt floorDiv(const SlowDynamicAPInt &LHS,
                                             const SlowDynamicAPInt &RHS);
   /// The operands must be non-negative for gcd.
-  LLVM_ABI_FRIEND friend SlowDynamicAPInt gcd(const SlowDynamicAPInt &A,
+  LLVM_ABI friend SlowDynamicAPInt gcd(const SlowDynamicAPInt &A,
                                        const SlowDynamicAPInt &B);
 
   /// Overload to compute a hash_code for a SlowDynamicAPInt value.
-  LLVM_ABI_FRIEND friend hash_code
-  hash_value(const SlowDynamicAPInt &X); // NOLINT
+  LLVM_ABI friend hash_code hash_value(const SlowDynamicAPInt &X); // NOLINT
 
   // Make DynamicAPInt a friend so it can access Val directly.
   friend DynamicAPInt;

llvm/include/llvm/Bitcode/BitcodeReader.h

@@ -120,7 +120,7 @@ struct ParserCallbacks {
           IdentificationBit(IdentificationBit), ModuleBit(ModuleBit) {}
 
     // Calls the ctor.
-    LLVM_ABI_FRIEND friend Expected<BitcodeFileContents>
+    LLVM_ABI friend Expected<BitcodeFileContents>
     getBitcodeFileContents(MemoryBufferRef Buffer);
 
     Expected<std::unique_ptr<Module>>

llvm/include/llvm/CodeGen/MachineOperand.h

@@ -764,7 +764,7 @@ public:
   /// isIdenticalTo uses for comparison. It is thus suited for use in hash
   /// tables which use that function for equality comparisons only. This must
   /// stay exactly in sync with isIdenticalTo above.
-  LLVM_ABI_FRIEND friend hash_code hash_value(const MachineOperand &MO);
+  LLVM_ABI friend hash_code hash_value(const MachineOperand &MO);
 
   /// ChangeToImmediate - Replace this operand with a new immediate operand of
   /// the specified value.  If an operand is known to be an immediate already,

llvm/include/llvm/CodeGen/PseudoSourceValue.h

@@ -46,8 +46,8 @@ public:
 private:
   unsigned Kind;
   unsigned AddressSpace;
-  LLVM_ABI_FRIEND friend raw_ostream &
-  llvm::operator<<(raw_ostream &OS, const PseudoSourceValue *PSV);
+  LLVM_ABI friend raw_ostream &llvm::operator<<(raw_ostream &OS,
+                                                const PseudoSourceValue *PSV);
 
   friend class MachineMemOperand; // For printCustom().
   friend class MIRFormatter;      // For printCustom().

llvm/include/llvm/Config/llvm-config.h.cmake

@@ -110,6 +110,9 @@
 /* Define if building LLVM with BUILD_SHARED_LIBS */
 #cmakedefine LLVM_BUILD_SHARED_LIBS
 
+/* Define if exporting LLVM public interface for shared library */
+#cmakedefine LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS
+
 /* Define if building LLVM with LLVM_FORCE_USE_OLD_TOOLCHAIN_LIBS */
 #cmakedefine LLVM_FORCE_USE_OLD_TOOLCHAIN ${LLVM_FORCE_USE_OLD_TOOLCHAIN}
 

llvm/include/llvm/ExecutionEngine/Orc/LLJIT.h

@@ -42,8 +42,7 @@ class ExecutorProcessControl;
 class LLVM_ABI LLJIT {
   template <typename, typename, typename> friend class LLJITBuilderSetters;
 
-  LLVM_ABI_FRIEND friend Expected<JITDylibSP>
-  setUpGenericLLVMIRPlatform(LLJIT &J);
+  LLVM_ABI friend Expected<JITDylibSP> setUpGenericLLVMIRPlatform(LLJIT &J);
 
 public:
   /// Initializer support for LLJIT.

llvm/include/llvm/ExecutionEngine/Orc/SymbolStringPool.h

@@ -36,7 +36,7 @@ class SymbolStringPool {
   friend class SymbolStringPoolEntryUnsafe;
 
   // Implemented in DebugUtils.h.
-  LLVM_ABI_FRIEND friend raw_ostream &operator<<(raw_ostream &OS,
+  LLVM_ABI friend raw_ostream &operator<<(raw_ostream &OS,
                                           const SymbolStringPool &SSP);
 
 public:
@@ -94,8 +94,8 @@ public:
     return LHS.S < RHS.S;
   }
 
-  LLVM_ABI_FRIEND friend raw_ostream &
-  operator<<(raw_ostream &OS, const SymbolStringPtrBase &Sym);
+  LLVM_ABI friend raw_ostream &operator<<(raw_ostream &OS,
+                                          const SymbolStringPtrBase &Sym);
 
 #ifndef NDEBUG
   // Returns true if the pool entry's ref count is above zero (or if the entry

llvm/include/llvm/ExecutionEngine/RuntimeDyld.h

@@ -287,7 +287,7 @@ public:
   LLVM_ABI void finalizeWithMemoryManagerLocking();
 
 private:
-  LLVM_ABI_FRIEND friend void jitLinkForORC(
+  LLVM_ABI friend void jitLinkForORC(
       object::OwningBinary<object::ObjectFile> O,
       RuntimeDyld::MemoryManager &MemMgr, JITSymbolResolver &Resolver,
       bool ProcessAllSections,

llvm/include/llvm/IR/Function.h

@@ -783,9 +783,8 @@ public:
 
 private:
   // These need access to the underlying BB list.
-  LLVM_ABI_FRIEND friend void BasicBlock::removeFromParent();
-  LLVM_ABI_FRIEND friend iplist<BasicBlock>::iterator
-  BasicBlock::eraseFromParent();
+  LLVM_ABI friend void BasicBlock::removeFromParent();
+  LLVM_ABI friend iplist<BasicBlock>::iterator BasicBlock::eraseFromParent();
   template <class BB_t, class BB_i_t, class BI_t, class II_t>
   friend class InstIterator;
   friend class llvm::SymbolTableListTraits<llvm::BasicBlock>;

llvm/include/llvm/ProfileData/SampleProfWriter.h

@@ -193,7 +193,7 @@ private:
   /// cannot be skipped.
   bool MarkFlatProfiles = false;
 
-  LLVM_ABI_FRIEND friend ErrorOr<std::unique_ptr<SampleProfileWriter>>
+  LLVM_ABI friend ErrorOr<std::unique_ptr<SampleProfileWriter>>
   SampleProfileWriter::create(std::unique_ptr<raw_ostream> &OS,
                               SampleProfileFormat Format);
 };
@@ -225,7 +225,7 @@ protected:
   void addNames(const FunctionSamples &S);
 
 private:
-  LLVM_ABI_FRIEND friend ErrorOr<std::unique_ptr<SampleProfileWriter>>
+  LLVM_ABI friend ErrorOr<std::unique_ptr<SampleProfileWriter>>
   SampleProfileWriter::create(std::unique_ptr<raw_ostream> &OS,
                               SampleProfileFormat Format);
 };

llvm/include/llvm/Support/Compiler.h

@@ -171,11 +171,6 @@
 /// for both functions and classes. On windows its turned in to dllimport for
 /// library consumers, for other platforms its a default visibility attribute.
 ///
-/// LLVM_ABI_FRIEND is for annotating friend function declarations when the
-/// target function's original declaration is annotated with LLVM_ABI. This
-/// macro matches the LLVM_ABI macro on Windows, on other platforms it does
-/// nothing.
-///
 /// LLVM_C_ABI is used to annotated functions and data that need to be exported
 /// for the libllvm-c API. This used both for the llvm-c headers and for the
 /// functions declared in the different Target's c++ source files that don't
@@ -184,19 +179,10 @@
 // Marker to add to classes or functions in public headers that should not have
 // export macros added to them by the clang tool
 #define LLVM_ABI_NOT_EXPORTED
-#if defined(LLVM_BUILD_LLVM_DYLIB) || defined(LLVM_BUILD_SHARED_LIBS) ||       \
-    defined(LLVM_ENABLE_PLUGINS)
-// Some libraries like those for tablegen are linked in to tools that used
-// in the build so can't depend on the llvm shared library. If export macros
-// were left enabled when building these we would get duplicate or
-// missing symbol linker errors on windows.
-#if defined(LLVM_BUILD_STATIC)
-#define LLVM_ABI
-#define LLVM_ABI_FRIEND
-#define LLVM_TEMPLATE_ABI
-#define LLVM_EXPORT_TEMPLATE
-#define LLVM_ABI_EXPORT
-#elif defined(_WIN32) && !defined(__MINGW32__)
+// TODO(https://github.com/llvm/llvm-project/issues/145406): eliminate need for
+// two preprocessor definitions to gate LLVM_ABI macro definitions.
+#if defined(LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS) && !defined(LLVM_BUILD_STATIC)
+#if defined(_WIN32) && !defined(__MINGW32__)
 #if defined(LLVM_EXPORTS)
 #define LLVM_ABI __declspec(dllexport)
 #define LLVM_TEMPLATE_ABI
@@ -206,25 +192,24 @@
 #define LLVM_TEMPLATE_ABI __declspec(dllimport)
 #define LLVM_EXPORT_TEMPLATE
 #endif
-#define LLVM_ABI_FRIEND LLVM_ABI
 #define LLVM_ABI_EXPORT __declspec(dllexport)
-#elif defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) ||             \
+#elif __has_attribute(visibility)
+#if defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) ||               \
     defined(__MVS__) || defined(__CYGWIN__)
-#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
-#define LLVM_ABI_FRIEND
-#define LLVM_TEMPLATE_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI __attribute__((visibility("default")))
+#define LLVM_TEMPLATE_ABI LLVM_ABI
 #define LLVM_EXPORT_TEMPLATE
-#define LLVM_ABI_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI_EXPORT LLVM_ABI
 #elif defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)
-#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
-#define LLVM_ABI_FRIEND
+#define LLVM_ABI __attribute__((visibility("default")))
 #define LLVM_TEMPLATE_ABI
 #define LLVM_EXPORT_TEMPLATE
-#define LLVM_ABI_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI_EXPORT LLVM_ABI
 #endif
-#else
+#endif
+#endif
+#if !defined(LLVM_ABI)
 #define LLVM_ABI
-#define LLVM_ABI_FRIEND
 #define LLVM_TEMPLATE_ABI
 #define LLVM_EXPORT_TEMPLATE
 #define LLVM_ABI_EXPORT

llvm/include/llvm/Support/Error.h

@@ -1191,7 +1191,7 @@ private:
 /// (or Expected) and you want to call code that still returns
 /// std::error_codes.
 class LLVM_ABI ECError : public ErrorInfo<ECError> {
-  LLVM_ABI_FRIEND friend Error errorCodeToError(std::error_code);
+  LLVM_ABI friend Error errorCodeToError(std::error_code);
 
   void anchor() override;
 

llvm/include/llvm/Support/FileSystem.h

@@ -220,7 +220,7 @@ public:
 
 /// Represents the result of a call to sys::fs::status().
 class file_status : public basic_file_status {
-  LLVM_ABI_FRIEND friend bool equivalent(file_status A, file_status B);
+  LLVM_ABI friend bool equivalent(file_status A, file_status B);
 
 #if defined(LLVM_ON_UNIX)
   dev_t fs_st_dev = 0;

llvm/include/llvm/Support/JSON.h

@@ -531,7 +531,7 @@ private:
                                       llvm::StringRef, std::string, json::Array,
                                       json::Object>
       Union;
-  LLVM_ABI_FRIEND friend bool operator==(const Value &, const Value &);
+  LLVM_ABI friend bool operator==(const Value &, const Value &);
 };
 
 LLVM_ABI bool operator==(const Value &, const Value &);
@@ -713,7 +713,7 @@ class Path::Root {
   llvm::StringLiteral ErrorMessage;
   std::vector<Path::Segment> ErrorPath; // Only valid in error state. Reversed.
 
-  LLVM_ABI_FRIEND friend void Path::report(llvm::StringLiteral Message);
+  LLVM_ABI friend void Path::report(llvm::StringLiteral Message);
 
 public:
   Root(llvm::StringRef Name = "") : Name(Name), ErrorMessage("") {}

llvm/include/llvm/Support/Path.h

@@ -80,8 +80,8 @@ class const_iterator
   Style S = Style::native; ///< The path style to use.
 
   // An end iterator has Position = Path.size() + 1.
-  LLVM_ABI_FRIEND friend const_iterator begin(StringRef path, Style style);
-  LLVM_ABI_FRIEND friend const_iterator end(StringRef path);
+  LLVM_ABI friend const_iterator begin(StringRef path, Style style);
+  LLVM_ABI friend const_iterator end(StringRef path);
 
 public:
   reference operator*() const { return Component; }
@@ -105,8 +105,8 @@ class reverse_iterator
   size_t    Position = 0;  ///< The iterators current position within Path.
   Style S = Style::native; ///< The path style to use.
 
-  LLVM_ABI_FRIEND friend reverse_iterator rbegin(StringRef path, Style style);
-  LLVM_ABI_FRIEND friend reverse_iterator rend(StringRef path);
+  LLVM_ABI friend reverse_iterator rbegin(StringRef path, Style style);
+  LLVM_ABI friend reverse_iterator rend(StringRef path);
 
 public:
   reference operator*() const { return Component; }

llvm/include/llvm/Support/PrettyStackTrace.h

@@ -51,7 +51,7 @@ namespace llvm {
   /// constructed and destructed, they will add their symbolic frames to a
   /// virtual stack trace.  This gets dumped out if the program crashes.
   class LLVM_ABI PrettyStackTraceEntry {
-    LLVM_ABI_FRIEND friend PrettyStackTraceEntry *
+    LLVM_ABI friend PrettyStackTraceEntry *
     ReverseStackTrace(PrettyStackTraceEntry *);
 
     PrettyStackTraceEntry *NextEntry;

llvm/include/llvm/XRay/InstrumentationMap.h

@@ -85,7 +85,7 @@ private:
   FunctionAddressMap FunctionAddresses;
   FunctionAddressReverseMap FunctionIds;
 
-  LLVM_ABI_FRIEND friend Expected<InstrumentationMap>
+  LLVM_ABI friend Expected<InstrumentationMap>
       loadInstrumentationMap(StringRef);
 
 public:

llvm/include/llvm/XRay/Trace.h

@@ -51,7 +51,7 @@ class Trace {
 
   typedef std::vector<XRayRecord>::const_iterator citerator;
 
-  LLVM_ABI_FRIEND friend Expected<Trace> loadTrace(const DataExtractor &, bool);
+  LLVM_ABI friend Expected<Trace> loadTrace(const DataExtractor &, bool);
 
 public:
   using size_type = RecordVector::size_type;