Add cold attribute to one time construction APIs

Add cold attribute to one time construction APIs

[Aditya K]

This would help compiler optimize local static objects.

```
commit e2f299679ddf56a6d6d71ea9d589cd76b2ca107b
Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
Date:   Thu Aug 13 09:41:34 2020 -0700

    Add cold attribute to one time construction APIs
    
    __cxa_guard_acquire is used for only one purpose,
    namely guarding local static variable initialization,
    and since that purpose is definitionally cold, it should be attributed as cold.
    Similarly for __cxa_guard_release and __cxa_guard_abort

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index b1fad59d4..359e955a7 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -39,20 +39,24 @@
 // Macros for various attributes.
 //   _GLIBCXX_PURE
 //   _GLIBCXX_CONST
 //   _GLIBCXX_NORETURN
 //   _GLIBCXX_NOTHROW
 //   _GLIBCXX_VISIBILITY
 #ifndef _GLIBCXX_PURE
 # define _GLIBCXX_PURE __attribute__ ((__pure__))
 #endif
 
+#ifndef _GLIBCXX_COLD
+# define _GLIBCXX_COLD __attribute__ ((cold))
+#endif
+
 #ifndef _GLIBCXX_CONST
 # define _GLIBCXX_CONST __attribute__ ((__const__))
 #endif
 
 #ifndef _GLIBCXX_NORETURN
 # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
 #endif
 
 // See below for C++
 #ifndef _GLIBCXX_NOTHROW
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 000713ecd..24c1366e2 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -108,27 +108,27 @@ namespace __cxxabiv1
   __cxa_vec_delete2(void* __array_address, size_t __element_size,
 		    size_t __padding_size, __cxa_cdtor_type __destructor,
 		    void (*__dealloc) (void*));
 
   void
   __cxa_vec_delete3(void* __array_address, size_t __element_size,
 		    size_t __padding_size, __cxa_cdtor_type __destructor,
 		    void (*__dealloc) (void*, size_t));
 
   int
-  __cxa_guard_acquire(__guard*);
+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
 
   void
-  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   void
-  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   // DSO destruction.
   int
   __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
 
   void
   __cxa_finalize(void*);
 
   // TLS destruction.
   int
```

Re: Add cold attribute to one time construction APIs

[Aditya K]

Revised patch with _GLIBCXX_COLD added at the end.

```
commit 3dc9f9a8461b1c88e991ceb517e5fdd81f268d1e
Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
Date:   Thu Aug 13 09:41:34 2020 -0700

    Add cold attribute to one time construction APIs
    
    __cxa_guard_acquire is used for only one purpose,
    namely guarding local static variable initialization,
    and since that purpose is definitionally cold, it should be attributed as cold.
    Similarly for __cxa_guard_release and __cxa_guard_abort

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index b1fad59d4..f6f954eef 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -35,20 +35,21 @@
 
 // The datestamp of the C++ library in compressed ISO date format.
 #define __GLIBCXX__
 
 // Macros for various attributes.
 //   _GLIBCXX_PURE
 //   _GLIBCXX_CONST
 //   _GLIBCXX_NORETURN
 //   _GLIBCXX_NOTHROW
 //   _GLIBCXX_VISIBILITY
+//   _GLIBCXX_COLD
 #ifndef _GLIBCXX_PURE
 # define _GLIBCXX_PURE __attribute__ ((__pure__))
 #endif
 
 #ifndef _GLIBCXX_CONST
 # define _GLIBCXX_CONST __attribute__ ((__const__))
 #endif
 
 #ifndef _GLIBCXX_NORETURN
 # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
@@ -67,20 +68,24 @@
 #define _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
 
 #if _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
 # define _GLIBCXX_VISIBILITY(V) __attribute__ ((__visibility__ (#V)))
 #else
 // If this is not supplied by the OS-specific or CPU-specific
 // headers included below, it will be defined to an empty default.
 # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
 #endif
 
+#ifndef _GLIBCXX_COLD
+# define _GLIBCXX_COLD __attribute__ ((cold))
+#endif
+
 // Macros for deprecated attributes.
 //   _GLIBCXX_USE_DEPRECATED
 //   _GLIBCXX_DEPRECATED
 //   _GLIBCXX17_DEPRECATED
 //   _GLIBCXX20_DEPRECATED( string-literal )
 #ifndef _GLIBCXX_USE_DEPRECATED
 # define _GLIBCXX_USE_DEPRECATED 1
 #endif
 
 #if defined(__DEPRECATED) && (__cplusplus >= 201103L)
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 000713ecd..24c1366e2 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -108,27 +108,27 @@ namespace __cxxabiv1
   __cxa_vec_delete2(void* __array_address, size_t __element_size,
 		    size_t __padding_size, __cxa_cdtor_type __destructor,
 		    void (*__dealloc) (void*));
 
   void
   __cxa_vec_delete3(void* __array_address, size_t __element_size,
 		    size_t __padding_size, __cxa_cdtor_type __destructor,
 		    void (*__dealloc) (void*, size_t));
 
   int
-  __cxa_guard_acquire(__guard*);
+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
 
   void
-  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   void
-  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   // DSO destruction.
   int
   __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
 
   void
   __cxa_finalize(void*);
 
   // TLS destruction.
   int
```

From: Aditya K
Sent: Thursday, August 13, 2020 10:47 AM
To: Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org>; jwakely.gcc@gmail.com <jwakely.gcc@gmail.com>
Subject: Add cold attribute to one time construction APIs 
 
This would help compiler optimize local static objects.

```
commit e2f299679ddf56a6d6d71ea9d589cd76b2ca107b
Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
Date:   Thu Aug 13 09:41:34 2020 -0700

    Add cold attribute to one time construction APIs
    
    __cxa_guard_acquire is used for only one purpose,
    namely guarding local static variable initialization,
    and since that purpose is definitionally cold, it should be attributed as cold.
    Similarly for __cxa_guard_release and __cxa_guard_abort

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index b1fad59d4..359e955a7 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -39,20 +39,24 @@
 // Macros for various attributes.
 //   _GLIBCXX_PURE
 //   _GLIBCXX_CONST
 //   _GLIBCXX_NORETURN
 //   _GLIBCXX_NOTHROW
 //   _GLIBCXX_VISIBILITY
 #ifndef _GLIBCXX_PURE
 # define _GLIBCXX_PURE __attribute__ ((__pure__))
 #endif
 
+#ifndef _GLIBCXX_COLD
+# define _GLIBCXX_COLD __attribute__ ((cold))
+#endif
+
 #ifndef _GLIBCXX_CONST
 # define _GLIBCXX_CONST __attribute__ ((__const__))
 #endif
 
 #ifndef _GLIBCXX_NORETURN
 # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
 #endif
 
 // See below for C++
 #ifndef _GLIBCXX_NOTHROW
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 000713ecd..24c1366e2 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -108,27 +108,27 @@ namespace __cxxabiv1
   __cxa_vec_delete2(void* __array_address, size_t __element_size,
                     size_t __padding_size, __cxa_cdtor_type __destructor,
                     void (*__dealloc) (void*));
 
   void
   __cxa_vec_delete3(void* __array_address, size_t __element_size,
                     size_t __padding_size, __cxa_cdtor_type __destructor,
                     void (*__dealloc) (void*, size_t));
 
   int
-  __cxa_guard_acquire(__guard*);
+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
 
   void
-  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   void
-  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   // DSO destruction.
   int
   __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
 
   void
   __cxa_finalize(void*);
 
   // TLS destruction.
   int
```

Re: Add cold attribute to one time construction APIs

[Aditya K]

FYI libc++ patch sent for review: https://reviews.llvm.org/D85873

Re: Add cold attribute to one time construction APIs

[Jonathan Wakely]

Please CC the libstdc++ list on all libstdc++ patches.

On Thu, 13 Aug 2020 at 17:51, Aditya K <hiraditya@msn.com> wrote:
>
> Revised patch with _GLIBCXX_COLD added at the end.
>
> ```
> commit 3dc9f9a8461b1c88e991ceb517e5fdd81f268d1e
> Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
> Date:   Thu Aug 13 09:41:34 2020 -0700
>
>     Add cold attribute to one time construction APIs
>
>     __cxa_guard_acquire is used for only one purpose,
>     namely guarding local static variable initialization,
>     and since that purpose is definitionally cold, it should be attributed as cold.
>     Similarly for __cxa_guard_release and __cxa_guard_abort
>
> diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
> index b1fad59d4..f6f954eef 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -35,20 +35,21 @@
>
>  // The datestamp of the C++ library in compressed ISO date format.
>  #define __GLIBCXX__
>
>  // Macros for various attributes.
>  //   _GLIBCXX_PURE
>  //   _GLIBCXX_CONST
>  //   _GLIBCXX_NORETURN
>  //   _GLIBCXX_NOTHROW
>  //   _GLIBCXX_VISIBILITY
> +//   _GLIBCXX_COLD
>  #ifndef _GLIBCXX_PURE
>  # define _GLIBCXX_PURE __attribute__ ((__pure__))
>  #endif
>
>  #ifndef _GLIBCXX_CONST
>  # define _GLIBCXX_CONST __attribute__ ((__const__))
>  #endif
>
>  #ifndef _GLIBCXX_NORETURN
>  # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
> @@ -67,20 +68,24 @@
>  #define _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
>
>  #if _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
>  # define _GLIBCXX_VISIBILITY(V) __attribute__ ((__visibility__ (#V)))
>  #else
>  // If this is not supplied by the OS-specific or CPU-specific
>  // headers included below, it will be defined to an empty default.
>  # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
>  #endif
>
> +#ifndef _GLIBCXX_COLD
> +# define _GLIBCXX_COLD __attribute__ ((cold))
> +#endif
> +
>  // Macros for deprecated attributes.
>  //   _GLIBCXX_USE_DEPRECATED
>  //   _GLIBCXX_DEPRECATED
>  //   _GLIBCXX17_DEPRECATED
>  //   _GLIBCXX20_DEPRECATED( string-literal )
>  #ifndef _GLIBCXX_USE_DEPRECATED
>  # define _GLIBCXX_USE_DEPRECATED 1
>  #endif
>
>  #if defined(__DEPRECATED) && (__cplusplus >= 201103L)
> diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
> index 000713ecd..24c1366e2 100644
> --- a/libstdc++-v3/libsupc++/cxxabi.h
> +++ b/libstdc++-v3/libsupc++/cxxabi.h
> @@ -108,27 +108,27 @@ namespace __cxxabiv1
>    __cxa_vec_delete2(void* __array_address, size_t __element_size,
>                     size_t __padding_size, __cxa_cdtor_type __destructor,
>                     void (*__dealloc) (void*));
>
>    void
>    __cxa_vec_delete3(void* __array_address, size_t __element_size,
>                     size_t __padding_size, __cxa_cdtor_type __destructor,
>                     void (*__dealloc) (void*, size_t));
>
>    int
> -  __cxa_guard_acquire(__guard*);
> +  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    // DSO destruction.
>    int
>    __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
>
>    void
>    __cxa_finalize(void*);
>
>    // TLS destruction.
>    int
> ```
>
> From: Aditya K
> Sent: Thursday, August 13, 2020 10:47 AM
> To: Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org>; jwakely.gcc@gmail.com <jwakely.gcc@gmail.com>
> Subject: Add cold attribute to one time construction APIs
>
> This would help compiler optimize local static objects.
>
> ```
> commit e2f299679ddf56a6d6d71ea9d589cd76b2ca107b
> Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
> Date:   Thu Aug 13 09:41:34 2020 -0700
>
>     Add cold attribute to one time construction APIs
>
>     __cxa_guard_acquire is used for only one purpose,
>     namely guarding local static variable initialization,
>     and since that purpose is definitionally cold, it should be attributed as cold.
>     Similarly for __cxa_guard_release and __cxa_guard_abort
>
> diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
> index b1fad59d4..359e955a7 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -39,20 +39,24 @@
>  // Macros for various attributes.
>  //   _GLIBCXX_PURE
>  //   _GLIBCXX_CONST
>  //   _GLIBCXX_NORETURN
>  //   _GLIBCXX_NOTHROW
>  //   _GLIBCXX_VISIBILITY
>  #ifndef _GLIBCXX_PURE
>  # define _GLIBCXX_PURE __attribute__ ((__pure__))
>  #endif
>
> +#ifndef _GLIBCXX_COLD
> +# define _GLIBCXX_COLD __attribute__ ((cold))
> +#endif
> +
>  #ifndef _GLIBCXX_CONST
>  # define _GLIBCXX_CONST __attribute__ ((__const__))
>  #endif
>
>  #ifndef _GLIBCXX_NORETURN
>  # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
>  #endif
>
>  // See below for C++
>  #ifndef _GLIBCXX_NOTHROW
> diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
> index 000713ecd..24c1366e2 100644
> --- a/libstdc++-v3/libsupc++/cxxabi.h
> +++ b/libstdc++-v3/libsupc++/cxxabi.h
> @@ -108,27 +108,27 @@ namespace __cxxabiv1
>    __cxa_vec_delete2(void* __array_address, size_t __element_size,
>                      size_t __padding_size, __cxa_cdtor_type __destructor,
>                      void (*__dealloc) (void*));
>
>    void
>    __cxa_vec_delete3(void* __array_address, size_t __element_size,
>                      size_t __padding_size, __cxa_cdtor_type __destructor,
>                      void (*__dealloc) (void*, size_t));
>
>    int
> -  __cxa_guard_acquire(__guard*);
> +  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    // DSO destruction.
>    int
>    __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
>
>    void
>    __cxa_finalize(void*);
>
>    // TLS destruction.
>    int
> ```

Re: Add cold attribute to one time construction APIs

[Aditya K]

sure.
--

From: Jonathan Wakely <jwakely.gcc@gmail.com>
Sent: Thursday, August 13, 2020 11:13 AM
To: Aditya K <hiraditya@msn.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>; gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: Add cold attribute to one time construction APIs 
 
Please CC the libstdc++ list on all libstdc++ patches.

On Thu, 13 Aug 2020 at 17:51, Aditya K <hiraditya@msn.com> wrote:
>
> Revised patch with _GLIBCXX_COLD added at the end.
>
> ```
> commit 3dc9f9a8461b1c88e991ceb517e5fdd81f268d1e
> Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
> Date:   Thu Aug 13 09:41:34 2020 -0700
>
>     Add cold attribute to one time construction APIs
>
>     __cxa_guard_acquire is used for only one purpose,
>     namely guarding local static variable initialization,
>     and since that purpose is definitionally cold, it should be attributed as cold.
>     Similarly for __cxa_guard_release and __cxa_guard_abort
>
> diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
> index b1fad59d4..f6f954eef 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -35,20 +35,21 @@
>
>  // The datestamp of the C++ library in compressed ISO date format.
>  #define __GLIBCXX__
>
>  // Macros for various attributes.
>  //   _GLIBCXX_PURE
>  //   _GLIBCXX_CONST
>  //   _GLIBCXX_NORETURN
>  //   _GLIBCXX_NOTHROW
>  //   _GLIBCXX_VISIBILITY
> +//   _GLIBCXX_COLD
>  #ifndef _GLIBCXX_PURE
>  # define _GLIBCXX_PURE __attribute__ ((__pure__))
>  #endif
>
>  #ifndef _GLIBCXX_CONST
>  # define _GLIBCXX_CONST __attribute__ ((__const__))
>  #endif
>
>  #ifndef _GLIBCXX_NORETURN
>  # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
> @@ -67,20 +68,24 @@
>  #define _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
>
>  #if _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
>  # define _GLIBCXX_VISIBILITY(V) __attribute__ ((__visibility__ (#V)))
>  #else
>  // If this is not supplied by the OS-specific or CPU-specific
>  // headers included below, it will be defined to an empty default.
>  # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
>  #endif
>
> +#ifndef _GLIBCXX_COLD
> +# define _GLIBCXX_COLD __attribute__ ((cold))
> +#endif
> +
>  // Macros for deprecated attributes.
>  //   _GLIBCXX_USE_DEPRECATED
>  //   _GLIBCXX_DEPRECATED
>  //   _GLIBCXX17_DEPRECATED
>  //   _GLIBCXX20_DEPRECATED( string-literal )
>  #ifndef _GLIBCXX_USE_DEPRECATED
>  # define _GLIBCXX_USE_DEPRECATED 1
>  #endif
>
>  #if defined(__DEPRECATED) && (__cplusplus >= 201103L)
> diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
> index 000713ecd..24c1366e2 100644
> --- a/libstdc++-v3/libsupc++/cxxabi.h
> +++ b/libstdc++-v3/libsupc++/cxxabi.h
> @@ -108,27 +108,27 @@ namespace __cxxabiv1
>    __cxa_vec_delete2(void* __array_address, size_t __element_size,
>                     size_t __padding_size, __cxa_cdtor_type __destructor,
>                     void (*__dealloc) (void*));
>
>    void
>    __cxa_vec_delete3(void* __array_address, size_t __element_size,
>                     size_t __padding_size, __cxa_cdtor_type __destructor,
>                     void (*__dealloc) (void*, size_t));
>
>    int
> -  __cxa_guard_acquire(__guard*);
> +  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    // DSO destruction.
>    int
>    __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
>
>    void
>    __cxa_finalize(void*);
>
>    // TLS destruction.
>    int
> ```
>
> From: Aditya K
> Sent: Thursday, August 13, 2020 10:47 AM
> To: Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org>; jwakely.gcc@gmail.com <jwakely.gcc@gmail.com>
> Subject: Add cold attribute to one time construction APIs
>
> This would help compiler optimize local static objects.
>
> ```
> commit e2f299679ddf56a6d6d71ea9d589cd76b2ca107b
> Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
> Date:   Thu Aug 13 09:41:34 2020 -0700
>
>     Add cold attribute to one time construction APIs
>
>     __cxa_guard_acquire is used for only one purpose,
>     namely guarding local static variable initialization,
>     and since that purpose is definitionally cold, it should be attributed as cold.
>     Similarly for __cxa_guard_release and __cxa_guard_abort
>
> diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
> index b1fad59d4..359e955a7 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -39,20 +39,24 @@
>  // Macros for various attributes.
>  //   _GLIBCXX_PURE
>  //   _GLIBCXX_CONST
>  //   _GLIBCXX_NORETURN
>  //   _GLIBCXX_NOTHROW
>  //   _GLIBCXX_VISIBILITY
>  #ifndef _GLIBCXX_PURE
>  # define _GLIBCXX_PURE __attribute__ ((__pure__))
>  #endif
>
> +#ifndef _GLIBCXX_COLD
> +# define _GLIBCXX_COLD __attribute__ ((cold))
> +#endif
> +
>  #ifndef _GLIBCXX_CONST
>  # define _GLIBCXX_CONST __attribute__ ((__const__))
>  #endif
>
>  #ifndef _GLIBCXX_NORETURN
>  # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
>  #endif
>
>  // See below for C++
>  #ifndef _GLIBCXX_NOTHROW
> diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
> index 000713ecd..24c1366e2 100644
> --- a/libstdc++-v3/libsupc++/cxxabi.h
> +++ b/libstdc++-v3/libsupc++/cxxabi.h
> @@ -108,27 +108,27 @@ namespace __cxxabiv1
>    __cxa_vec_delete2(void* __array_address, size_t __element_size,
>                      size_t __padding_size, __cxa_cdtor_type __destructor,
>                      void (*__dealloc) (void*));
>
>    void
>    __cxa_vec_delete3(void* __array_address, size_t __element_size,
>                      size_t __padding_size, __cxa_cdtor_type __destructor,
>                      void (*__dealloc) (void*, size_t));
>
>    int
> -  __cxa_guard_acquire(__guard*);
> +  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    void
> -  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
> +  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
>
>    // DSO destruction.
>    int
>    __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
>
>    void
>    __cxa_finalize(void*);
>
>    // TLS destruction.
>    int
> ```

Re: [PATCH] Add cold attribute to one time construction APIs

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 3802 bytes --]

On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote:
>This would help compiler optimize local static objects.
>
>Added changelog.

Please don't :-)

GCC patch policies always said NOT to change the ChangeLog in the
patch, because the ChangeLog files change so rapidly that it means by
the time you've sent the patch, it no longer applies.

Current GCC policies are that NOBODY changes the ChangeLog files, they
are autogenerated from Git commit logs once per day.

So please just include the proposed ChangeLog entry as the Git commit
message in the body of your email.

Patch for libstdc++ need to go to both the libstdc++ list and the
gcc-patches list, in the same email. Not sent once to each list as
separate emails.

>
>```
From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001
>From: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
>Date: Thu, 13 Aug 2020 09:41:34 -0700
>Subject: [PATCH] Add cold attribute to one time construction APIs
>
>__cxa_guard_acquire is used for only one purpose,
>namely guarding local static variable initialization,
>and since that purpose is definitionally cold, it should be attributed as cold.

Definitionally isn't a word. Attributed is a word, but it doesn't mean
marked with an attribute.

>Similarly for __cxa_guard_release and __cxa_guard_abort
>---
> libstdc++-v3/ChangeLog              | 5 +++++
> libstdc++-v3/include/bits/c++config | 5 +++++
> libstdc++-v3/libsupc++/cxxabi.h     | 6 +++---
> 3 files changed, 13 insertions(+), 3 deletions(-)
>
>diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
>index fe6884bf3..86b707ac7 100644
>--- a/libstdc++-v3/ChangeLog
>+++ b/libstdc++-v3/ChangeLog
>@@ -1,3 +1,8 @@
>+2020-08-17  Aditya Kumar  <hiraditya@msn.com>
>+	* libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute
>+	* libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release,
>+	__cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute.

The changelog format is wrong. There should be a blank line after the
date+author line, and you're adding _GLIBCXX_COLD not
_GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above.

> 2020-08-14  Lewis Hyatt  <lhyatt@gmail.com>
>
> 	* testsuite/lib/libstdc++.exp: Use the new option
>diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
>index b1fad59d4..f6f954eef 100644
>--- a/libstdc++-v3/include/bits/c++config
>+++ b/libstdc++-v3/include/bits/c++config
>@@ -42,6 +42,7 @@
> //   _GLIBCXX_NORETURN
> //   _GLIBCXX_NOTHROW
> //   _GLIBCXX_VISIBILITY
>+//   _GLIBCXX_COLD
> #ifndef _GLIBCXX_PURE
> # define _GLIBCXX_PURE __attribute__ ((__pure__))
> #endif
>@@ -74,6 +75,10 @@
> # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
> #endif
>
>+#ifndef _GLIBCXX_COLD
>+# define _GLIBCXX_COLD __attribute__ ((cold))
>+#endif

"cold" is not a reserved name so this needs to be __cold__.

I'm not sure we really need it in <bits/c++config.h> if we only use it
in one file, but maybe we'll find more uses for it later.

>diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
>index 000713ecd..24c1366e2 100644
>--- a/libstdc++-v3/libsupc++/cxxabi.h
>+++ b/libstdc++-v3/libsupc++/cxxabi.h
>@@ -115,13 +115,13 @@ namespace __cxxabiv1
> 		    void (*__dealloc) (void*, size_t));
>
>   int
>-  __cxa_guard_acquire(__guard*);
>+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;

The GCC manual says that functions marked cold will be optimized for
size not for speed. Is that really what we want here?

It makes sense to put them in a cold section, but I think we still
want them to be optimized for speed, don't we?

I've attached a patch addressing the issues above, but I'd like to
know whether the change to how the functions are optimized is
desirable, or even noticable.


[-- Attachment #2: cold.patch.txt --]
[-- Type: text/plain, Size: 2062 bytes --]

commit fadd79179f93c82c2935fdfe17a2ab1586b4e70f
Author: Aditya Kumar <hiraditya@msn.com>
Date:   Tue Aug 18 15:22:24 2020

    libstdc++: Add cold attribute to one time construction APIs
    
    __cxa_guard_acquire is used for only one purpose, namely guarding local
    static variable initialization. Since that purpose happens rarely, it
    should be marked with the 'cold' attribute.
    
    Similarly for __cxa_guard_release and __cxa_guard_abort.
    
    libstdc++-v3/ChangeLog:
    
    2020-08-18  Aditya Kumar  <hiraditya@msn.com>
    
            * include/bits/c++config (_GLIBCXX_COLD): Define.
            * libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release)
            (__cxa_guard_abort): Add _GLIBCXX_COLD.

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index b1fad59d4b3..a135de00a50 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -42,6 +42,7 @@
 //   _GLIBCXX_NORETURN
 //   _GLIBCXX_NOTHROW
 //   _GLIBCXX_VISIBILITY
+//   _GLIBCXX_COLD
 #ifndef _GLIBCXX_PURE
 # define _GLIBCXX_PURE __attribute__ ((__pure__))
 #endif
@@ -74,6 +75,10 @@
 # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
 #endif
 
+#ifndef _GLIBCXX_COLD
+# define _GLIBCXX_COLD __attribute__ ((__cold__))
+#endif
+
 // Macros for deprecated attributes.
 //   _GLIBCXX_USE_DEPRECATED
 //   _GLIBCXX_DEPRECATED
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 000713ecdf8..24c1366e271 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -115,13 +115,13 @@ namespace __cxxabiv1
 		    void (*__dealloc) (void*, size_t));
 
   int
-  __cxa_guard_acquire(__guard*);
+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
 
   void
-  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   void
-  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   // DSO destruction.
   int

Re: [PATCH] Add cold attribute to one time construction APIs

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 3157 bytes --]

On 18/08/20 15:35 +0100, Jonathan Wakely wrote:
>On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote:
>>This would help compiler optimize local static objects.
>>
>>Added changelog.
>
>Please don't :-)
>
>GCC patch policies always said NOT to change the ChangeLog in the
>patch, because the ChangeLog files change so rapidly that it means by
>the time you've sent the patch, it no longer applies.
>
>Current GCC policies are that NOBODY changes the ChangeLog files, they
>are autogenerated from Git commit logs once per day.
>
>So please just include the proposed ChangeLog entry as the Git commit
>message in the body of your email.
>
>Patch for libstdc++ need to go to both the libstdc++ list and the
>gcc-patches list, in the same email. Not sent once to each list as
>separate emails.
>
>>
>>```
>From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001
>>From: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
>>Date: Thu, 13 Aug 2020 09:41:34 -0700
>>Subject: [PATCH] Add cold attribute to one time construction APIs
>>
>>__cxa_guard_acquire is used for only one purpose,
>>namely guarding local static variable initialization,
>>and since that purpose is definitionally cold, it should be attributed as cold.
>
>Definitionally isn't a word. Attributed is a word, but it doesn't mean
>marked with an attribute.
>
>>Similarly for __cxa_guard_release and __cxa_guard_abort
>>---
>>libstdc++-v3/ChangeLog              | 5 +++++
>>libstdc++-v3/include/bits/c++config | 5 +++++
>>libstdc++-v3/libsupc++/cxxabi.h     | 6 +++---
>>3 files changed, 13 insertions(+), 3 deletions(-)
>>
>>diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
>>index fe6884bf3..86b707ac7 100644
>>--- a/libstdc++-v3/ChangeLog
>>+++ b/libstdc++-v3/ChangeLog
>>@@ -1,3 +1,8 @@
>>+2020-08-17  Aditya Kumar  <hiraditya@msn.com>
>>+	* libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute
>>+	* libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release,
>>+	__cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute.
>
>The changelog format is wrong. There should be a blank line after the
>date+author line, and you're adding _GLIBCXX_COLD not
>_GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above.
>
>>2020-08-14  Lewis Hyatt  <lhyatt@gmail.com>
>>
>>	* testsuite/lib/libstdc++.exp: Use the new option
>>diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
>>index b1fad59d4..f6f954eef 100644
>>--- a/libstdc++-v3/include/bits/c++config
>>+++ b/libstdc++-v3/include/bits/c++config
>>@@ -42,6 +42,7 @@
>>//   _GLIBCXX_NORETURN
>>//   _GLIBCXX_NOTHROW
>>//   _GLIBCXX_VISIBILITY
>>+//   _GLIBCXX_COLD
>>#ifndef _GLIBCXX_PURE
>># define _GLIBCXX_PURE __attribute__ ((__pure__))
>>#endif
>>@@ -74,6 +75,10 @@
>># define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
>>#endif
>>
>>+#ifndef _GLIBCXX_COLD
>>+# define _GLIBCXX_COLD __attribute__ ((cold))
>>+#endif
>
>"cold" is not a reserved name so this needs to be __cold__.

I've just pushed the attached patch which ensures we don't use the
non-reserved form of the attribute.

Tested x86_64-linux, committed to trunk.


[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 4210 bytes --]

commit 6c1a58b7fbdaa8ac00957fccfb379af163309311
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 18 15:37:14 2020

    libstdc++: Add "cold" to tests for reserved attribute names
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/17_intro/headers/c++1998/all_attributes.cc: Check
            "cold" isn't used in the library. Also check <cxxabi.h>.
            * testsuite/17_intro/headers/c++2011/all_attributes.cc:
            Likewise.
            * testsuite/17_intro/headers/c++2014/all_attributes.cc:
            Likewise.
            * testsuite/17_intro/headers/c++2017/all_attributes.cc:
            Likewise.
            * testsuite/17_intro/headers/c++2020/all_attributes.cc:
            Likewise.

diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc
index 73a20e346e4..dd28429e1d5 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc
@@ -21,6 +21,7 @@
 // Ensure the library only uses the __name__ form for attributes.
 // Don't test 'const' because it is reserved anyway.
 #define abi_tag 1
+#define cold 1
 #ifndef __APPLE__
 // darwin headers use these, see PR 64883
 # define always_inline 1
@@ -36,6 +37,7 @@
 #endif
 
 #include <bits/extc++.h>
+#include <cxxabi.h>
 
 int
 main()
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc
index c0a79e06ddc..db00a33f6a3 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc
@@ -21,6 +21,7 @@
 // Ensure the library only uses the __name__ form for attributes.
 // Don't test 'const' and 'noreturn' because they are reserved anyway.
 #define abi_tag 1
+#define cold 1
 #ifndef __APPLE__
 // darwin headers use these, see PR 64883
 # define always_inline 1
@@ -35,6 +36,7 @@
 #endif
 
 #include <bits/extc++.h>
+#include <cxxabi.h>
 
 int
 main()
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc
index 1e3ba0888a0..3322c2c1362 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc
@@ -21,6 +21,7 @@
 // Ensure the library only uses the __name__ form for attributes.
 // Don't test 'const' and 'noreturn' because they are reserved anyway.
 #define abi_tag 1
+#define cold 1
 #ifndef __APPLE__
 // darwin headers use these, see PR 64883
 # define always_inline 1
@@ -35,6 +36,7 @@
 #endif
 
 #include <bits/extc++.h>
+#include <cxxabi.h>
 
 int
 main()
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++2017/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++2017/all_attributes.cc
index 035526e24cb..a0d67739d71 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++2017/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++2017/all_attributes.cc
@@ -21,6 +21,7 @@
 // Ensure the library only uses the __name__ form for attributes.
 // Don't test 'const' and 'noreturn' because they are reserved anyway.
 #define abi_tag 1
+#define cold 1
 #ifndef __APPLE__
 // darwin headers use these, see PR 64883
 # define always_inline 1
@@ -34,6 +35,7 @@
 #endif
 
 #include <bits/extc++.h>
+#include <cxxabi.h>
 
 int
 main()
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++2020/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++2020/all_attributes.cc
index 6f5ea460fac..da8f0e415a3 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++2020/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++2020/all_attributes.cc
@@ -21,6 +21,7 @@
 // Ensure the library only uses the __name__ form for attributes.
 // Don't test 'const' and 'noreturn' because they are reserved anyway.
 #define abi_tag 1
+#define cold 1
 #ifndef __APPLE__
 // darwin headers use these, see PR 64883
 # define always_inline 1
@@ -34,6 +35,7 @@
 #endif
 
 #include <bits/extc++.h>
+#include <cxxabi.h>
 
 int
 main()

Re: [PATCH] Add cold attribute to one time construction APIs

[Richard Biener]

On Tue, Aug 18, 2020 at 4:36 PM Jonathan Wakely via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote:
> >This would help compiler optimize local static objects.
> >
> >Added changelog.
>
> Please don't :-)
>
> GCC patch policies always said NOT to change the ChangeLog in the
> patch, because the ChangeLog files change so rapidly that it means by
> the time you've sent the patch, it no longer applies.
>
> Current GCC policies are that NOBODY changes the ChangeLog files, they
> are autogenerated from Git commit logs once per day.
>
> So please just include the proposed ChangeLog entry as the Git commit
> message in the body of your email.
>
> Patch for libstdc++ need to go to both the libstdc++ list and the
> gcc-patches list, in the same email. Not sent once to each list as
> separate emails.
>
> >
> >```
> >From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001
> >From: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
> >Date: Thu, 13 Aug 2020 09:41:34 -0700
> >Subject: [PATCH] Add cold attribute to one time construction APIs
> >
> >__cxa_guard_acquire is used for only one purpose,
> >namely guarding local static variable initialization,
> >and since that purpose is definitionally cold, it should be attributed as cold.
>
> Definitionally isn't a word. Attributed is a word, but it doesn't mean
> marked with an attribute.
>
> >Similarly for __cxa_guard_release and __cxa_guard_abort
> >---
> > libstdc++-v3/ChangeLog              | 5 +++++
> > libstdc++-v3/include/bits/c++config | 5 +++++
> > libstdc++-v3/libsupc++/cxxabi.h     | 6 +++---
> > 3 files changed, 13 insertions(+), 3 deletions(-)
> >
> >diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
> >index fe6884bf3..86b707ac7 100644
> >--- a/libstdc++-v3/ChangeLog
> >+++ b/libstdc++-v3/ChangeLog
> >@@ -1,3 +1,8 @@
> >+2020-08-17  Aditya Kumar  <hiraditya@msn.com>
> >+      * libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute
> >+      * libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release,
> >+      __cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute.
>
> The changelog format is wrong. There should be a blank line after the
> date+author line, and you're adding _GLIBCXX_COLD not
> _GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above.
>
> > 2020-08-14  Lewis Hyatt  <lhyatt@gmail.com>
> >
> >       * testsuite/lib/libstdc++.exp: Use the new option
> >diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
> >index b1fad59d4..f6f954eef 100644
> >--- a/libstdc++-v3/include/bits/c++config
> >+++ b/libstdc++-v3/include/bits/c++config
> >@@ -42,6 +42,7 @@
> > //   _GLIBCXX_NORETURN
> > //   _GLIBCXX_NOTHROW
> > //   _GLIBCXX_VISIBILITY
> >+//   _GLIBCXX_COLD
> > #ifndef _GLIBCXX_PURE
> > # define _GLIBCXX_PURE __attribute__ ((__pure__))
> > #endif
> >@@ -74,6 +75,10 @@
> > # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
> > #endif
> >
> >+#ifndef _GLIBCXX_COLD
> >+# define _GLIBCXX_COLD __attribute__ ((cold))
> >+#endif
>
> "cold" is not a reserved name so this needs to be __cold__.
>
> I'm not sure we really need it in <bits/c++config.h> if we only use it
> in one file, but maybe we'll find more uses for it later.
>
> >diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
> >index 000713ecd..24c1366e2 100644
> >--- a/libstdc++-v3/libsupc++/cxxabi.h
> >+++ b/libstdc++-v3/libsupc++/cxxabi.h
> >@@ -115,13 +115,13 @@ namespace __cxxabiv1
> >                   void (*__dealloc) (void*, size_t));
> >
> >   int
> >-  __cxa_guard_acquire(__guard*);
> >+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>
> The GCC manual says that functions marked cold will be optimized for
> size not for speed. Is that really what we want here?
>
> It makes sense to put them in a cold section, but I think we still
> want them to be optimized for speed, don't we?
>
> I've attached a patch addressing the issues above, but I'd like to
> know whether the change to how the functions are optimized is
> desirable, or even noticable.

Hmm, but the functions are always executed?  The .cold sections
are so they are not paged in and this particular case would defeat
this purpose?

Richard.

>

Re: [PATCH] Add cold attribute to one time construction APIs

[Jan Hubicka]

> On Tue, Aug 18, 2020 at 4:36 PM Jonathan Wakely via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote:
> > >This would help compiler optimize local static objects.
> > >
> > >Added changelog.
> >
> > Please don't :-)
> >
> > GCC patch policies always said NOT to change the ChangeLog in the
> > patch, because the ChangeLog files change so rapidly that it means by
> > the time you've sent the patch, it no longer applies.
> >
> > Current GCC policies are that NOBODY changes the ChangeLog files, they
> > are autogenerated from Git commit logs once per day.
> >
> > So please just include the proposed ChangeLog entry as the Git commit
> > message in the body of your email.
> >
> > Patch for libstdc++ need to go to both the libstdc++ list and the
> > gcc-patches list, in the same email. Not sent once to each list as
> > separate emails.
> >
> > >
> > >```
> > >From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001
> > >From: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
> > >Date: Thu, 13 Aug 2020 09:41:34 -0700
> > >Subject: [PATCH] Add cold attribute to one time construction APIs
> > >
> > >__cxa_guard_acquire is used for only one purpose,
> > >namely guarding local static variable initialization,
> > >and since that purpose is definitionally cold, it should be attributed as cold.
> >
> > Definitionally isn't a word. Attributed is a word, but it doesn't mean
> > marked with an attribute.
> >
> > >Similarly for __cxa_guard_release and __cxa_guard_abort
> > >---
> > > libstdc++-v3/ChangeLog              | 5 +++++
> > > libstdc++-v3/include/bits/c++config | 5 +++++
> > > libstdc++-v3/libsupc++/cxxabi.h     | 6 +++---
> > > 3 files changed, 13 insertions(+), 3 deletions(-)
> > >
> > >diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
> > >index fe6884bf3..86b707ac7 100644
> > >--- a/libstdc++-v3/ChangeLog
> > >+++ b/libstdc++-v3/ChangeLog
> > >@@ -1,3 +1,8 @@
> > >+2020-08-17  Aditya Kumar  <hiraditya@msn.com>
> > >+      * libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute
> > >+      * libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release,
> > >+      __cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute.
> >
> > The changelog format is wrong. There should be a blank line after the
> > date+author line, and you're adding _GLIBCXX_COLD not
> > _GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above.
> >
> > > 2020-08-14  Lewis Hyatt  <lhyatt@gmail.com>
> > >
> > >       * testsuite/lib/libstdc++.exp: Use the new option
> > >diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
> > >index b1fad59d4..f6f954eef 100644
> > >--- a/libstdc++-v3/include/bits/c++config
> > >+++ b/libstdc++-v3/include/bits/c++config
> > >@@ -42,6 +42,7 @@
> > > //   _GLIBCXX_NORETURN
> > > //   _GLIBCXX_NOTHROW
> > > //   _GLIBCXX_VISIBILITY
> > >+//   _GLIBCXX_COLD
> > > #ifndef _GLIBCXX_PURE
> > > # define _GLIBCXX_PURE __attribute__ ((__pure__))
> > > #endif
> > >@@ -74,6 +75,10 @@
> > > # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
> > > #endif
> > >
> > >+#ifndef _GLIBCXX_COLD
> > >+# define _GLIBCXX_COLD __attribute__ ((cold))
> > >+#endif
> >
> > "cold" is not a reserved name so this needs to be __cold__.
> >
> > I'm not sure we really need it in <bits/c++config.h> if we only use it
> > in one file, but maybe we'll find more uses for it later.
> >
> > >diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
> > >index 000713ecd..24c1366e2 100644
> > >--- a/libstdc++-v3/libsupc++/cxxabi.h
> > >+++ b/libstdc++-v3/libsupc++/cxxabi.h
> > >@@ -115,13 +115,13 @@ namespace __cxxabiv1
> > >                   void (*__dealloc) (void*, size_t));
> > >
> > >   int
> > >-  __cxa_guard_acquire(__guard*);
> > >+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
> >
> > The GCC manual says that functions marked cold will be optimized for
> > size not for speed. Is that really what we want here?
> >
> > It makes sense to put them in a cold section, but I think we still
> > want them to be optimized for speed, don't we?
> >
> > I've attached a patch addressing the issues above, but I'd like to
> > know whether the change to how the functions are optimized is
> > desirable, or even noticable.
> 
> Hmm, but the functions are always executed?  The .cold sections
> are so they are not paged in and this particular case would defeat
> this purpose?

We have internal attribute for functions executed at startup and exit.
We could export that via attribute to users if that helps.  Note that
GCC is able to propagate this info in easy enough examples.

But if I am right, this is used for EH and we generally drop EH into
cold section.

Honza
> 
> Richard.
> 
> >

Re: [PATCH] Add cold attribute to one time construction APIs

[Jonathan Wakely]

On 24/08/20 10:09 +0200, Jan Hubicka wrote:
>> On Tue, Aug 18, 2020 at 4:36 PM Jonathan Wakely via Gcc-patches
>> <gcc-patches@gcc.gnu.org> wrote:
>> >
>> > On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote:
>> > >This would help compiler optimize local static objects.
>> > >
>> > >Added changelog.
>> >
>> > Please don't :-)
>> >
>> > GCC patch policies always said NOT to change the ChangeLog in the
>> > patch, because the ChangeLog files change so rapidly that it means by
>> > the time you've sent the patch, it no longer applies.
>> >
>> > Current GCC policies are that NOBODY changes the ChangeLog files, they
>> > are autogenerated from Git commit logs once per day.
>> >
>> > So please just include the proposed ChangeLog entry as the Git commit
>> > message in the body of your email.
>> >
>> > Patch for libstdc++ need to go to both the libstdc++ list and the
>> > gcc-patches list, in the same email. Not sent once to each list as
>> > separate emails.
>> >
>> > >
>> > >```
>> > >From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001
>> > >From: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
>> > >Date: Thu, 13 Aug 2020 09:41:34 -0700
>> > >Subject: [PATCH] Add cold attribute to one time construction APIs
>> > >
>> > >__cxa_guard_acquire is used for only one purpose,
>> > >namely guarding local static variable initialization,
>> > >and since that purpose is definitionally cold, it should be attributed as cold.
>> >
>> > Definitionally isn't a word. Attributed is a word, but it doesn't mean
>> > marked with an attribute.
>> >
>> > >Similarly for __cxa_guard_release and __cxa_guard_abort
>> > >---
>> > > libstdc++-v3/ChangeLog              | 5 +++++
>> > > libstdc++-v3/include/bits/c++config | 5 +++++
>> > > libstdc++-v3/libsupc++/cxxabi.h     | 6 +++---
>> > > 3 files changed, 13 insertions(+), 3 deletions(-)
>> > >
>> > >diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
>> > >index fe6884bf3..86b707ac7 100644
>> > >--- a/libstdc++-v3/ChangeLog
>> > >+++ b/libstdc++-v3/ChangeLog
>> > >@@ -1,3 +1,8 @@
>> > >+2020-08-17  Aditya Kumar  <hiraditya@msn.com>
>> > >+      * libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute
>> > >+      * libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release,
>> > >+      __cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute.
>> >
>> > The changelog format is wrong. There should be a blank line after the
>> > date+author line, and you're adding _GLIBCXX_COLD not
>> > _GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above.
>> >
>> > > 2020-08-14  Lewis Hyatt  <lhyatt@gmail.com>
>> > >
>> > >       * testsuite/lib/libstdc++.exp: Use the new option
>> > >diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
>> > >index b1fad59d4..f6f954eef 100644
>> > >--- a/libstdc++-v3/include/bits/c++config
>> > >+++ b/libstdc++-v3/include/bits/c++config
>> > >@@ -42,6 +42,7 @@
>> > > //   _GLIBCXX_NORETURN
>> > > //   _GLIBCXX_NOTHROW
>> > > //   _GLIBCXX_VISIBILITY
>> > >+//   _GLIBCXX_COLD
>> > > #ifndef _GLIBCXX_PURE
>> > > # define _GLIBCXX_PURE __attribute__ ((__pure__))
>> > > #endif
>> > >@@ -74,6 +75,10 @@
>> > > # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
>> > > #endif
>> > >
>> > >+#ifndef _GLIBCXX_COLD
>> > >+# define _GLIBCXX_COLD __attribute__ ((cold))
>> > >+#endif
>> >
>> > "cold" is not a reserved name so this needs to be __cold__.
>> >
>> > I'm not sure we really need it in <bits/c++config.h> if we only use it
>> > in one file, but maybe we'll find more uses for it later.
>> >
>> > >diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
>> > >index 000713ecd..24c1366e2 100644
>> > >--- a/libstdc++-v3/libsupc++/cxxabi.h
>> > >+++ b/libstdc++-v3/libsupc++/cxxabi.h
>> > >@@ -115,13 +115,13 @@ namespace __cxxabiv1
>> > >                   void (*__dealloc) (void*, size_t));
>> > >
>> > >   int
>> > >-  __cxa_guard_acquire(__guard*);
>> > >+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>> >
>> > The GCC manual says that functions marked cold will be optimized for
>> > size not for speed. Is that really what we want here?
>> >
>> > It makes sense to put them in a cold section, but I think we still
>> > want them to be optimized for speed, don't we?
>> >
>> > I've attached a patch addressing the issues above, but I'd like to
>> > know whether the change to how the functions are optimized is
>> > desirable, or even noticable.
>>
>> Hmm, but the functions are always executed?  The .cold sections

They're not *guaranteed* to be executed. But they're executed every
time control passes over the definition of a local static variable.

So making them cold is probably wrong.

The __cxa_guard_abort function could be cold, because that's only used
if the local static being constructed throws an exception from its
constructor. But guard_acquire and guard_release could theoretically
be called frequently in hot code (though it's not a good idea to make
a hot function use local statics with non-trivial initialization,
precisely because that needs to call these external functions).

>> are so they are not paged in and this particular case would defeat
>> this purpose?
>
>We have internal attribute for functions executed at startup and exit.

These are for local statics, which are not constructed at startup.
They are destroyed at exit though.

>We could export that via attribute to users if that helps.  Note that
>GCC is able to propagate this info in easy enough examples.
>
>But if I am right, this is used for EH and we generally drop EH into
>cold section.

These are for constructing local static variables, not for EH.

Re: [PATCH] Add cold attribute to one time construction APIs

[Jonathan Wakely]

On 24/08/20 09:45 +0100, Jonathan Wakely via Libstdc++ wrote:
>On 24/08/20 10:09 +0200, Jan Hubicka wrote:
>>>On Tue, Aug 18, 2020 at 4:36 PM Jonathan Wakely via Gcc-patches
>>><gcc-patches@gcc.gnu.org> wrote:
>>>>
>>>> On 17/08/20 18:15 +0000, Aditya K via Libstdc++ wrote:
>>>> >This would help compiler optimize local static objects.
>>>> >
>>>> >Added changelog.
>>>>
>>>> Please don't :-)
>>>>
>>>> GCC patch policies always said NOT to change the ChangeLog in the
>>>> patch, because the ChangeLog files change so rapidly that it means by
>>>> the time you've sent the patch, it no longer applies.
>>>>
>>>> Current GCC policies are that NOBODY changes the ChangeLog files, they
>>>> are autogenerated from Git commit logs once per day.
>>>>
>>>> So please just include the proposed ChangeLog entry as the Git commit
>>>> message in the body of your email.
>>>>
>>>> Patch for libstdc++ need to go to both the libstdc++ list and the
>>>> gcc-patches list, in the same email. Not sent once to each list as
>>>> separate emails.
>>>>
>>>> >
>>>> >```
>>>> >From c6cba40e0434147db89d3af05b598782cde651e3 Mon Sep 17 00:00:00 2001
>>>> >From: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
>>>> >Date: Thu, 13 Aug 2020 09:41:34 -0700
>>>> >Subject: [PATCH] Add cold attribute to one time construction APIs
>>>> >
>>>> >__cxa_guard_acquire is used for only one purpose,
>>>> >namely guarding local static variable initialization,
>>>> >and since that purpose is definitionally cold, it should be attributed as cold.
>>>>
>>>> Definitionally isn't a word. Attributed is a word, but it doesn't mean
>>>> marked with an attribute.
>>>>
>>>> >Similarly for __cxa_guard_release and __cxa_guard_abort
>>>> >---
>>>> > libstdc++-v3/ChangeLog              | 5 +++++
>>>> > libstdc++-v3/include/bits/c++config | 5 +++++
>>>> > libstdc++-v3/libsupc++/cxxabi.h     | 6 +++---
>>>> > 3 files changed, 13 insertions(+), 3 deletions(-)
>>>> >
>>>> >diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
>>>> >index fe6884bf3..86b707ac7 100644
>>>> >--- a/libstdc++-v3/ChangeLog
>>>> >+++ b/libstdc++-v3/ChangeLog
>>>> >@@ -1,3 +1,8 @@
>>>> >+2020-08-17  Aditya Kumar  <hiraditya@msn.com>
>>>> >+      * libstdc++-v3/include/bits/c++config: Add _GLIBCXX_NOTHROW attribute
>>>> >+      * libstdc++-v3/libsupc++/cxxabi.h (__cxa_guard_acquire, __cxa_guard_release,
>>>> >+      __cxa_guard_abort): Add _GLIBCXX_NOTHROW attribute.
>>>>
>>>> The changelog format is wrong. There should be a blank line after the
>>>> date+author line, and you're adding _GLIBCXX_COLD not
>>>> _GLIBCXX_NOTHROW. But it shouldn't be here at all as explained above.
>>>>
>>>> > 2020-08-14  Lewis Hyatt  <lhyatt@gmail.com>
>>>> >
>>>> >       * testsuite/lib/libstdc++.exp: Use the new option
>>>> >diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
>>>> >index b1fad59d4..f6f954eef 100644
>>>> >--- a/libstdc++-v3/include/bits/c++config
>>>> >+++ b/libstdc++-v3/include/bits/c++config
>>>> >@@ -42,6 +42,7 @@
>>>> > //   _GLIBCXX_NORETURN
>>>> > //   _GLIBCXX_NOTHROW
>>>> > //   _GLIBCXX_VISIBILITY
>>>> >+//   _GLIBCXX_COLD
>>>> > #ifndef _GLIBCXX_PURE
>>>> > # define _GLIBCXX_PURE __attribute__ ((__pure__))
>>>> > #endif
>>>> >@@ -74,6 +75,10 @@
>>>> > # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
>>>> > #endif
>>>> >
>>>> >+#ifndef _GLIBCXX_COLD
>>>> >+# define _GLIBCXX_COLD __attribute__ ((cold))
>>>> >+#endif
>>>>
>>>> "cold" is not a reserved name so this needs to be __cold__.
>>>>
>>>> I'm not sure we really need it in <bits/c++config.h> if we only use it
>>>> in one file, but maybe we'll find more uses for it later.
>>>>
>>>> >diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
>>>> >index 000713ecd..24c1366e2 100644
>>>> >--- a/libstdc++-v3/libsupc++/cxxabi.h
>>>> >+++ b/libstdc++-v3/libsupc++/cxxabi.h
>>>> >@@ -115,13 +115,13 @@ namespace __cxxabiv1
>>>> >                   void (*__dealloc) (void*, size_t));
>>>> >
>>>> >   int
>>>> >-  __cxa_guard_acquire(__guard*);
>>>> >+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
>>>>
>>>> The GCC manual says that functions marked cold will be optimized for
>>>> size not for speed. Is that really what we want here?
>>>>
>>>> It makes sense to put them in a cold section, but I think we still
>>>> want them to be optimized for speed, don't we?
>>>>
>>>> I've attached a patch addressing the issues above, but I'd like to
>>>> know whether the change to how the functions are optimized is
>>>> desirable, or even noticable.
>>>
>>>Hmm, but the functions are always executed?  The .cold sections
>
>They're not *guaranteed* to be executed. But they're executed every
>time control passes over the definition of a local static variable.
>
>So making them cold is probably wrong.
>
>The __cxa_guard_abort function could be cold, because that's only used
>if the local static being constructed throws an exception from its
>constructor. But guard_acquire and guard_release could theoretically
>be called frequently in hot code (though it's not a good idea to make
>a hot function use local statics with non-trivial initialization,
>precisely because that needs to call these external functions).
>
>>>are so they are not paged in and this particular case would defeat
>>>this purpose?
>>
>>We have internal attribute for functions executed at startup and exit.
>
>These are for local statics, which are not constructed at startup.
>They are destroyed at exit though.

But these functions aren't used for the destruction, atexit is used to
register the destruction.

>>We could export that via attribute to users if that helps.  Note that
>>GCC is able to propagate this info in easy enough examples.
>>
>>But if I am right, this is used for EH and we generally drop EH into
>>cold section.
>
>These are for constructing local static variables, not for EH.
>
>