[llvm] Add __attribute__((__retain__)) to LLVM_ATTRIBUTE_USED (PR #133025)

[Matthias Braun via llvm-commits]

https://github.com/MatzeB updated https://github.com/llvm/llvm-project/pull/133025

>From 619901e8163c9f7e9691d1215ca263ece7afdb22 Mon Sep 17 00:00:00 2001
From: Matthias Braun <matze at braunis.de>
Date: Tue, 25 Mar 2025 18:16:27 -0700
Subject: [PATCH 1/2] Add __attribute__((__retain__)) to LLVM_ATTRIBUTE_USED

Without the retain attribute the dump functions will be stripped when
LLVM is compiled with `-ffunction-section -Wl,--gc-sections` on
ELF-based systems.
---
 llvm/include/llvm/Support/Compiler.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index dc8b5389069eb..b6d06238f8d83 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -224,7 +224,9 @@
 #define LLVM_PREFETCH(addr, rw, locality)
 #endif
 
-#if __has_attribute(used)
+#if __has_attribute(used) && __has_attribute(retain)
+#define LLVM_ATTRIBUTE_USED __attribute__((__used__, __retain__))
+#elif __has_attribute(used)
 #define LLVM_ATTRIBUTE_USED __attribute__((__used__))
 #else
 #define LLVM_ATTRIBUTE_USED

>From 584a2db08aaf66dffd9be66a47257107e16acc20 Mon Sep 17 00:00:00 2001
From: Matthias Braun <matze at braunis.de>
Date: Wed, 26 Mar 2025 09:58:08 -0700
Subject: [PATCH 2/2] Add separate LLVM_ATTRIBUTE_RETAIN macro

---
 llvm/include/llvm/Support/Compiler.h | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index b6d06238f8d83..ff6f5e44ae2f1 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -224,14 +224,18 @@
 #define LLVM_PREFETCH(addr, rw, locality)
 #endif
 
-#if __has_attribute(used) && __has_attribute(retain)
-#define LLVM_ATTRIBUTE_USED __attribute__((__used__, __retain__))
-#elif __has_attribute(used)
+#if __has_attribute(used)
 #define LLVM_ATTRIBUTE_USED __attribute__((__used__))
 #else
 #define LLVM_ATTRIBUTE_USED
 #endif
 
+#if __has_attribute(retain)
+#define LLVM_ATTRIBUTE_RETAIN __attribute__((__retain__))
+#else
+#define LLVM_ATTRIBUTE_RETAIN
+#endif
+
 #if defined(__clang__)
 #define LLVM_DEPRECATED(MSG, FIX) __attribute__((deprecated(MSG, FIX)))
 #else
@@ -621,7 +625,8 @@ void AnnotateIgnoreWritesEnd(const char *file, int line);
 /// get stripped in release builds.
 // FIXME: Move this to a private config.h as it's not usable in public headers.
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-#define LLVM_DUMP_METHOD LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED
+#define LLVM_DUMP_METHOD                                                       \
+  LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED LLVM_ATTRIBUTE_RETAIN
 #else
 #define LLVM_DUMP_METHOD LLVM_ATTRIBUTE_NOINLINE
 #endif