[llvm] [llvm] revisions to export annotation macros to avoid compiler warnings (PR #135995)
Andrew Rogers via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 16 10:57:32 PDT 2025
https://github.com/andrurogerz created https://github.com/llvm/llvm-project/pull/135995
## Purpose
Revise the `LLVM_ABI` family of macros defined in `llvm/Support/Compiler.h` to eliminate GCC compiler warnings that appear when more of the codebase is annotated.
## Overview
This patch changes the annotation behavior in two ways:
1. Switches the macros to explicitly use the `__annotation__((visibility("default")))` syntax rather than rely on the pre-existing `LLVM_ATTRIBUTE_VISIBILITY_DEFAULT`. The `LLVM_ATTRIBUTE_VISIBILITY_DEFAULT` macro resolves to `[[gnu::visibility("default")]]` on most compiler versions, which is permitted in fewer locations (such as annotating `friend` function declarations) and produces warnings.
2. Defines `LLVM_TEMPLATE_ABI` to nothing when compiling with GCC. This avoids compiler warnings about redefined attributes on explicitly instantiated template types.
## Background
Additional context on the effort to annotate LLVM's public interface is in [this discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307).
Without this change, compiling LLVM with GCC produces `-Wattributes` warnings in a number of cases when more of the codebase has been annotated. None of these warnings are present when compiling with Clang.
>From 7aeebfd91857b18e5335edf00728d3c71339835f Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Tue, 15 Apr 2025 17:07:27 -0700
Subject: [PATCH 1/4] [llvm] use __attribute__ for export visibility macros
---
llvm/include/llvm/Support/Compiler.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index d265d864228ca..7b490d7db4dcf 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -199,15 +199,15 @@
#define LLVM_ABI_EXPORT __declspec(dllexport)
#elif defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
defined(__MVS__)
-#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
-#define LLVM_TEMPLATE_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI __attribute__((visibility("default")))
+#define LLVM_TEMPLATE_ABI __attribute__((visibility("default")))
#define LLVM_EXPORT_TEMPLATE
-#define LLVM_ABI_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
#elif defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)
-#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI __attribute__((visibility("default")))
#define LLVM_TEMPLATE_ABI
#define LLVM_EXPORT_TEMPLATE
-#define LLVM_ABI_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
#endif
#else
#define LLVM_ABI
>From c57be05d0a7613f91837fd124108bb6819d252f4 Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Tue, 15 Apr 2025 17:07:54 -0700
Subject: [PATCH 2/4] [llvm] do not define LLVM_TEMPLATE_ABI for GCC builds
---
llvm/include/llvm/Support/Compiler.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index 7b490d7db4dcf..fd103ea72e55c 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -200,7 +200,12 @@
#elif defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
defined(__MVS__)
#define LLVM_ABI __attribute__((visibility("default")))
+#if defined(__GNUC__) && !defined(__clang__)
+// GCC produces warnings on visibility attributes applied to templates.
+#define LLVM_TEMPLATE_ABI
+#else
#define LLVM_TEMPLATE_ABI __attribute__((visibility("default")))
+#endif
#define LLVM_EXPORT_TEMPLATE
#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
#elif defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)
>From 3d62cf05b5ac87c3a2cd4560b67c7155bb6b83ae Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Wed, 16 Apr 2025 09:15:22 -0700
Subject: [PATCH 3/4] [llvm] check for visibility attribute
---
llvm/include/llvm/Support/Compiler.h | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index fd103ea72e55c..5dfac827e615c 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -197,8 +197,8 @@
#define LLVM_EXPORT_TEMPLATE
#endif
#define LLVM_ABI_EXPORT __declspec(dllexport)
-#elif defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
- defined(__MVS__)
+#elif (defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
+ defined(__MVS__)) && __has_attribute(visibililty)
#define LLVM_ABI __attribute__((visibility("default")))
#if defined(__GNUC__) && !defined(__clang__)
// GCC produces warnings on visibility attributes applied to templates.
@@ -208,11 +208,17 @@
#endif
#define LLVM_EXPORT_TEMPLATE
#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
-#elif defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)
+#elif (defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)) && \
+ __has_attribute(visibility)
#define LLVM_ABI __attribute__((visibility("default")))
#define LLVM_TEMPLATE_ABI
#define LLVM_EXPORT_TEMPLATE
#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
+#else
+#define LLVM_ABI
+#define LLVM_TEMPLATE_ABI
+#define LLVM_EXPORT_TEMPLATE
+#define LLVM_ABI_EXPORT
#endif
#else
#define LLVM_ABI
>From 74ed68fcb6cfc3b804ce21b79c35282edb484278 Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Wed, 16 Apr 2025 10:33:48 -0700
Subject: [PATCH 4/4] [llvm] additional comments
---
llvm/include/llvm/Support/Compiler.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index 5dfac827e615c..d24d78a5b3c1d 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -199,9 +199,12 @@
#define LLVM_ABI_EXPORT __declspec(dllexport)
#elif (defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
defined(__MVS__)) && __has_attribute(visibililty)
+// Use __attribute__((visibility(""))) syntax for visibility rather than
+// [[gnu::visibility("")]] because compilers are more permissive with its
+// placement.
#define LLVM_ABI __attribute__((visibility("default")))
#if defined(__GNUC__) && !defined(__clang__)
-// GCC produces warnings on visibility attributes applied to templates.
+// GCC produces warnings on visibility attributes applied to some templates.
#define LLVM_TEMPLATE_ABI
#else
#define LLVM_TEMPLATE_ABI __attribute__((visibility("default")))
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