[ASan][libc++] Refactor of ASan annotation functions

[AdvenamTacet]

This commit refactors the ASan annotation functions in libc++ to reduce unnecessary code duplication. Additionally it adds a small optimization.

• Eliminates two redundant function versions by utilizing the [[maybe_unused]] attribute and guarding function bodies with #ifndef _LIBCPP_HAS_NO_ASAN.
• Introduces an additional guard to an auxiliary function, allowing the removal of a no-ops function body. This approach avoids relying on the optimizer for code elimination.

Suggested by @ldionne in #73043

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Tacet (AdvenamTacet)

Changes

This commit refactors the ASan annotation functions in libc++ to reduce unnecessary code duplication.

• Eliminates two redundant function versions by utilizing the [[maybe_unused]] attribute and guarding function bodies with #ifndef _LIBCPP_HAS_NO_ASAN.
• Introduces an additional guard to an auxiliary function, allowing the removal of a no-ops function body. This approach avoids relying on the optimizer for code elimination.

Suggested by @ldionne in #73043

---

Full diff: https://github.com/llvm/llvm-project/pull/74023.diff

2 Files Affected:

• (modified) libcxx/include/deque (+15-12)
• (modified) libcxx/include/vector (+8-9)

diff --git a/libcxx/include/deque b/libcxx/include/deque
index 1438f1e992e203f..5fd7b25cc81220a 100644
--- a/libcxx/include/deque
+++ b/libcxx/include/deque
@@ -966,25 +966,27 @@ public:
 // __asan_annotate_container_with_allocator to false.
 // For more details, see the "Using libc++" documentation page or
 // the documentation for __sanitizer_annotate_contiguous_container.
-#if !defined(_LIBCPP_HAS_NO_ASAN)
     _LIBCPP_HIDE_FROM_ABI void __annotate_double_ended_contiguous_container(
-        const void* __beg,
-        const void* __end,
-        const void* __old_con_beg,
-        const void* __old_con_end,
-        const void* __new_con_beg,
-        const void* __new_con_end) const {
+       [[__maybe_unused__]] const void* __beg,
+       [[__maybe_unused__]] const void* __end,
+       [[__maybe_unused__]] const void* __old_con_beg,
+       [[__maybe_unused__]] const void* __old_con_end,
+       [[__maybe_unused__]] const void* __new_con_beg,
+       [[__maybe_unused__]] const void* __new_con_end) const {
+#ifndef _LIBCPP_HAS_NO_ASAN
         if (__beg != nullptr && __asan_annotate_container_with_allocator<_Allocator>::value)
             __sanitizer_annotate_double_ended_contiguous_container(
                 __beg, __end, __old_con_beg, __old_con_end, __new_con_beg, __new_con_end);
+#endif
     }
-#else
-    _LIBCPP_HIDE_FROM_ABI void __annotate_double_ended_contiguous_container(
-        const void*, const void*, const void*, const void*, const void*, const void*) const _NOEXCEPT {}
-#endif // !defined(_LIBCPP_HAS_NO_ASAN)
 
     _LIBCPP_HIDE_FROM_ABI
-    void __annotate_from_to(size_type __beg, size_type __end, __asan_annotation_type __annotation_type, __asan_annotation_place __place) const _NOEXCEPT {
+    void __annotate_from_to(
+            [[__maybe_unused__]] size_type __beg,
+            [[__maybe_unused__]] size_type __end,
+            [[__maybe_unused__]] __asan_annotation_type __annotation_type,
+            [[__maybe_unused__]] __asan_annotation_place __place) const _NOEXCEPT {
+#ifndef _LIBCPP_HAS_NO_ASAN
         // __beg - index of the first item to annotate
         // __end - index behind the last item to annotate (so last item + 1)
         // __annotation_type - __asan_unposion or __asan_poison
@@ -1075,6 +1077,7 @@ public:
 
             __annotate_double_ended_contiguous_container(__mem_beg, __mem_end, __old_beg, __old_end, __new_beg, __new_end);
         }
+#endif
     }
 
     _LIBCPP_HIDE_FROM_ABI
diff --git a/libcxx/include/vector b/libcxx/include/vector
index 4ec6b602371eaee..fe3d3895be979a7 100644
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -846,20 +846,19 @@ private:
     // __asan_annotate_container_with_allocator to false.
     // For more details, see the "Using libc++" documentation page or
     // the documentation for __sanitizer_annotate_contiguous_container.
-#ifndef _LIBCPP_HAS_NO_ASAN
+
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    void __annotate_contiguous_container(const void *__beg, const void *__end,
-                                         const void *__old_mid,
-                                         const void *__new_mid) const
+    void __annotate_contiguous_container([[__maybe_unused__]] const void *__beg,
+                                         [[__maybe_unused__]] const void *__end,
+                                         [[__maybe_unused__]] const void *__old_mid,
+                                         [[__maybe_unused__]] const void *__new_mid) const
     {
+#ifndef _LIBCPP_HAS_NO_ASAN
       if (!__libcpp_is_constant_evaluated() && __beg != nullptr && __asan_annotate_container_with_allocator<_Allocator>::value)
         __sanitizer_annotate_contiguous_container(__beg, __end, __old_mid, __new_mid);
-    }
-#else
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
-    void __annotate_contiguous_container(const void*, const void*, const void*,
-                                         const void*) const _NOEXCEPT {}
 #endif
+    }
+
     _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
     void __annotate_new(size_type __current_size) const _NOEXCEPT {
       __annotate_contiguous_container(data(), data() + capacity(),

[ldionne]

LGTM, thanks for the patch. I think this makes it clearer that this code is really not used when asan is disabled.