[libc++] Remove unnecessary includes from <atomic>

[philnik777]

This reduces the include time of <atomic> from 135ms to 88ms.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

This reduces the include time of <atomic> from 135ms to 88ms.

---

Full diff: https://github.com/llvm/llvm-project/pull/82880.diff

6 Files Affected:

• (modified) libcxx/include/__atomic/aliases.h (-1)
• (modified) libcxx/include/__config (+4)
• (modified) libcxx/include/__thread/support/pthread.h (+3-1)
• (modified) libcxx/include/atomic (+1)
• (modified) libcxx/test/libcxx/transitive_includes/cxx23.csv (-1)
• (modified) libcxx/test/libcxx/transitive_includes/cxx26.csv (-1)

diff --git a/libcxx/include/__atomic/aliases.h b/libcxx/include/__atomic/aliases.h
index 0fa289de54b0f1..a87099802737aa 100644
--- a/libcxx/include/__atomic/aliases.h
+++ b/libcxx/include/__atomic/aliases.h
@@ -18,7 +18,6 @@
 #include <__type_traits/make_unsigned.h>
 #include <cstddef>
 #include <cstdint>
-#include <cstdlib>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
diff --git a/libcxx/include/__config b/libcxx/include/__config
index 0797880cb2f5da..d9291bc4e185b4 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -460,6 +460,10 @@ _LIBCPP_HARDENING_MODE_DEBUG
 #    define __has_constexpr_builtin(x) 0
 #  endif
 
+#  ifndef __building_module
+#    define __building_module(...) 0
+#  endif
+
 // '__is_identifier' returns '0' if '__x' is a reserved identifier provided by
 // the compiler and '1' otherwise.
 #  ifndef __is_identifier
diff --git a/libcxx/include/__thread/support/pthread.h b/libcxx/include/__thread/support/pthread.h
index d0b8367e448f48..e82e8152f44007 100644
--- a/libcxx/include/__thread/support/pthread.h
+++ b/libcxx/include/__thread/support/pthread.h
@@ -30,7 +30,9 @@
 // so libc++'s <math.h> usually absorbs atomic_wide_counter.h into the
 // module with <math.h> and makes atomic_wide_counter.h invisible.
 // Include <math.h> here to work around that.
-#include <math.h>
+#if __building_module(std)
+#  include <math.h>
+#endif
 
 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
 #  pragma GCC system_header
diff --git a/libcxx/include/atomic b/libcxx/include/atomic
index 2e8f5b521a55eb..2dac69377b77f0 100644
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -620,6 +620,7 @@ template <class T>
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #  include <cmath>
 #  include <compare>
+#  include <cstdlib>
 #  include <cstring>
 #  include <type_traits>
 #endif
diff --git a/libcxx/test/libcxx/transitive_includes/cxx23.csv b/libcxx/test/libcxx/transitive_includes/cxx23.csv
index 44b5f78beea48b..49b3ac265487d7 100644
--- a/libcxx/test/libcxx/transitive_includes/cxx23.csv
+++ b/libcxx/test/libcxx/transitive_includes/cxx23.csv
@@ -30,7 +30,6 @@ array stdexcept
 array version
 atomic cstddef
 atomic cstdint
-atomic cstdlib
 atomic cstring
 atomic ctime
 atomic limits
diff --git a/libcxx/test/libcxx/transitive_includes/cxx26.csv b/libcxx/test/libcxx/transitive_includes/cxx26.csv
index 44b5f78beea48b..49b3ac265487d7 100644
--- a/libcxx/test/libcxx/transitive_includes/cxx26.csv
+++ b/libcxx/test/libcxx/transitive_includes/cxx26.csv
@@ -30,7 +30,6 @@ array stdexcept
 array version
 atomic cstddef
 atomic cstdint
-atomic cstdlib
 atomic cstring
 atomic ctime
 atomic limits

[mordante]

LGTM after addressing the review comments.

[mordante]

Please add comments to this #ifdef the name is very unfortunate, this seems to be about clang modules and not C++20 modules.

[mordante]

Please add comment about the module here too. __building_module(std) gives very strong vibes of being about the C++23 std module.