[llvm] DLLExport llvm::dbgs (PR #127854)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: Andrew Rogers (andrurogerz)

<details>
<summary>Changes</summary>

## Overview
Annotate the `llvm::dbgs` function so it is explicitly included in LLVM's public interface. When building LLVM as a Windows DLL, this annotation exports it from the DLL.

## Background
This change is required as part of the overall project to build LLVM as a Windows DLL described in #<!-- -->109483. Without this change, LLVM tools fail to link.

## Validation
Built LLVM with MSVC on Windows 11:
```
cmake -B build -S llvm -G Ninja -DCMAKE_BUILD_TYPE=Debug -DLLVM_ENABLE_PROJECTS="clang" -DLLVM_OPTIMIZED_TABLEGEN -DLLVM_BUILD_LLVM_DYLIB=ON -DLLVM_BUILD_LLVM_DYLIB_VIS=ON -DLLVM_LINK_LLVM_DYLIB=ON -DCLANG_LINK_CLANG_DYLIB=ON
ninja -C build llvm-rc llvm-ar
```
Verified the annotated interface no longer appears in the list of unresolved external symbols.

---
Full diff: https://github.com/llvm/llvm-project/pull/127854.diff


1 Files Affected:

- (modified) llvm/include/llvm/Support/Debug.h (+3-1) 


``````````diff
diff --git a/llvm/include/llvm/Support/Debug.h b/llvm/include/llvm/Support/Debug.h
index 23c54ac9bb4b1..9eef747d7496d 100644
--- a/llvm/include/llvm/Support/Debug.h
+++ b/llvm/include/llvm/Support/Debug.h
@@ -28,6 +28,8 @@
 #ifndef LLVM_SUPPORT_DEBUG_H
 #define LLVM_SUPPORT_DEBUG_H
 
+#include "llvm/Support/Compiler.h"
+
 namespace llvm {
 
 class raw_ostream;
@@ -94,7 +96,7 @@ extern bool EnableDebugBuffering;
 /// dbgs() - This returns a reference to a raw_ostream for debugging
 /// messages.  If debugging is disabled it returns errs().  Use it
 /// like: dbgs() << "foo" << "bar";
-raw_ostream &dbgs();
+LLVM_ABI raw_ostream &dbgs();
 
 // DEBUG macro - This macro should be used by passes to emit debug information.
 // If the '-debug' option is specified on the commandline, and if this is a

``````````

</details>


https://github.com/llvm/llvm-project/pull/127854