Add __attribute__((retain)) to LLVM_DUMP_METHOD

[MatzeB]

Without the retain attribute the dump functions will be stripped when
LLVM is compiled with -ffunction-section -Wl,--gc-sections on
ELF-based systems.

[MatzeB]

Some of our internal builds use -ffunction-sections -Wl,--gc-sections and I just noticed that we need an additional __attribute__((retain)) to keep the LLVM dump functions around.

Is there any downside to using this attribute in LLVM?

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Matthias Braun (MatzeB)

Changes

Without the retain attribute the dump functions will be stripped when
LLVM is compiled with -ffunction-section -Wl,--gc-sections on
ELF-based systems.

---

Full diff: https://github.com/llvm/llvm-project/pull/133025.diff

1 Files Affected:

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

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

[MaskRay]

Some of our internal builds use -ffunction-sections -Wl,--gc-sections and I just noticed that we need an additional __attribute__((retain)) to keep the LLVM dump functions around.

Is there any downside to using this attribute in LLVM?

Perhaps we should just add retained to LLVM_DUMP_METHOD?

This will enable USED functions to be garbage-collectable on ELF platforms, where this behavior has been consistently present.

[MatzeB]

Are you saying you rather have a separate macro for retain? Updated the PR to do that.

[MaskRay]

LGTM, the title needs an adjustment now.