[llvm] revisions to LLVM_ABI export macro definitions (llvm#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 <[email protected]>

Author: 2 people

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 @@ class IEEEFloat final {
   /// 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 @@ class IEEEFloat final {
   ///   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 @@ class DoubleAPFloat final {
   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,
-                                              roundingMode);
-  LLVM_ABI_FRIEND friend DoubleAPFloat frexp(const DoubleAPFloat &X, int &Exp,
-                                             roundingMode);
-  LLVM_ABI_FRIEND friend hash_code hash_value(const DoubleAPFloat &Arg);
+  LLVM_ABI friend DoubleAPFloat scalbn(const DoubleAPFloat &X, int Exp,
+                                       roundingMode);
+  LLVM_ABI friend DoubleAPFloat frexp(const DoubleAPFloat &X, int &Exp,
+                                      roundingMode);
+  LLVM_ABI friend hash_code hash_value(const DoubleAPFloat &Arg);
 };
 
 LLVM_ABI hash_code hash_value(const DoubleAPFloat &Arg);
@@ -1518,7 +1517,7 @@ class APFloat : public APFloatBase {
     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 @@ class SlowDynamicAPInt {
   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,
-                                                  const SlowDynamicAPInt &RHS);
-  LLVM_ABI_FRIEND friend SlowDynamicAPInt floorDiv(const SlowDynamicAPInt &LHS,
-                                                   const SlowDynamicAPInt &RHS);
+  LLVM_ABI friend SlowDynamicAPInt abs(const SlowDynamicAPInt &X);
+  LLVM_ABI friend SlowDynamicAPInt ceilDiv(const SlowDynamicAPInt &LHS,
+                                           const SlowDynamicAPInt &RHS);
+  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,
-                                              const SlowDynamicAPInt &B);
+  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 @@ class MachineOperand {
   /// 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 @@ class LLVM_ABI PseudoSourceValue {
 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

@@ -36,8 +36,8 @@ class SymbolStringPool {
   friend class SymbolStringPoolEntryUnsafe;
 
   // Implemented in DebugUtils.h.
-  LLVM_ABI_FRIEND friend raw_ostream &operator<<(raw_ostream &OS,
-                                                 const SymbolStringPool &SSP);
+  LLVM_ABI friend raw_ostream &operator<<(raw_ostream &OS,
+                                          const SymbolStringPool &SSP);
 
 public:
   /// Destroy a SymbolStringPool.
@@ -94,8 +94,8 @@ class SymbolStringPtrBase {
     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