Andrew Rogers 0580563299
[llvm] annotate interfaces in llvm-c for DLL export (#141701)
## Purpose

This patch is one in a series of code-mods that annotate LLVM’s public
interface for export. This patch annotates the `llvm-c` interface with a
new `LLVM_C_ABI` annotation, which behaves like the `LLVM_ABI`. This
annotation currently has no meaningful impact on the LLVM build;
however, it is a prerequisite to support an LLVM Windows DLL (shared
library) build.

## Overview

1. Add a new `llvm-c/Visibility.h` header file that defines a new
`LLVM_C_ABI` macro. The macro resolves to the proper DLL export/import
annotation on Windows and a "default" visibility annotation elsewhere.
2. Add a new `LLVM_ENABLE_LLVM_C_EXPORT_ANNOTATIONS` `#cmakedefine` that
is used to gate the definition of `LLVM_C_ABI`.
3. Remove the existing `LLVM_C_ABI` definition from
`llvm/Support/Compiler.h`. Update the small number of `LLVM_C_ABI`
references to get it from the new `llvm-c/Visibility.h` header.
4. Code-mod annotate the public `llvm-c` interface using the [Interface
Definition Scanner (IDS)](https://github.com/compnerd/ids) tool.
5. Format the changes with `clang-format`.

## Background

This effort is tracked in #109483. Additional context is provided in
[this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307),
and 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).

## Validation

Local builds and tests to validate cross-platform compatibility. This
included llvm, clang, and lldb on the following configurations:

- Windows with MSVC
- Windows with Clang
- Linux with GCC
- Linux with Clang
- Darwin with Clang
2025-07-08 08:50:21 -07:00

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/*===-- llvm-c/Linker.h - Module Linker C Interface -------------*- C++ -*-===*\
|* *|
|* Part of the LLVM Project, under the Apache License v2.0 with LLVM *|
|* Exceptions. *|
|* See https://llvm.org/LICENSE.txt for license information. *|
|* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception *|
|* *|
|*===----------------------------------------------------------------------===*|
|* *|
|* This file defines the C interface to the module/file/archive linker. *|
|* *|
\*===----------------------------------------------------------------------===*/
#ifndef LLVM_C_LINKER_H
#define LLVM_C_LINKER_H
#include "llvm-c/ExternC.h"
#include "llvm-c/Types.h"
#include "llvm-c/Visibility.h"
LLVM_C_EXTERN_C_BEGIN
/**
* @defgroup LLVMCCoreLinker Linker
* @ingroup LLVMCCore
*
* @{
*/
/* This enum is provided for backwards-compatibility only. It has no effect. */
typedef enum {
LLVMLinkerDestroySource = 0, /* This is the default behavior. */
LLVMLinkerPreserveSource_Removed = 1 /* This option has been deprecated and
should not be used. */
} LLVMLinkerMode;
/* Links the source module into the destination module. The source module is
* destroyed.
* The return value is true if an error occurred, false otherwise.
* Use the diagnostic handler to get any diagnostic message.
*/
LLVM_C_ABI LLVMBool LLVMLinkModules2(LLVMModuleRef Dest, LLVMModuleRef Src);
LLVM_C_EXTERN_C_END
/**
* @}
*/
#endif