From 92ce384c80999c59672c140057bdbd226f778ec5 Mon Sep 17 00:00:00 2001
From: Alexandre Duret-Lutz <adl@lrde.epita.fr>
Date: Mon, 11 Jan 2021 19:27:37 +0100
Subject: [PATCH] fix compilation of core/bricks with clang++10

* configure.ac: Call CHECK_ATOMIC after setting the C++ options.
This is probably not necessary, but it makes more sense.
* m4/l_atomic.m4: Augment the test body with a scenario
that actually requires -latomic.
---
 configure.ac   |  8 ++++----
 m4/l_atomic.m4 | 30 ++++++++++++++++++++++--------
 2 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/configure.ac b/configure.ac
index 3ad6f056a..ee32bd21b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Copyright (C) 2008-2020, Laboratoire de Recherche et Développement
+# Copyright (C) 2008-2021, Laboratoire de Recherche et Développement
 # de l'Epita (LRDE).
 # Copyright (C) 2003-2007 Laboratoire d'Informatique de Paris 6
 # (LIP6), département Systèmes Répartis Coopératifs (SRC), Université
@@ -79,9 +79,6 @@ AX_CHECK_COMPILE_FLAG([-std=c11], [CFLAGS="$CFLAGS -std=c11"])
 
 gl_INIT
 
-dnl Check if -latomic is required for <std::atomic>
-CHECK_ATOMIC
-
 # Use -Werror since using -fvisibility under MinGW is only a warning.
 # (The option is ignored anyway since this does not make sense under windows).
 AX_CHECK_COMPILE_FLAG([-Werror -fvisibility=hidden],
@@ -145,6 +142,9 @@ else
   fi
 fi
 
+dnl Check if -latomic is required for <std::atomic>
+CHECK_ATOMIC
+
 AX_CHECK_BUDDY
 
 AC_CHECK_HEADERS([sys/times.h valgrind/memcheck.h spawn.h])
diff --git a/m4/l_atomic.m4 b/m4/l_atomic.m4
index e423270ea..08e5b4f79 100644
--- a/m4/l_atomic.m4
+++ b/m4/l_atomic.m4
@@ -10,14 +10,28 @@ dnl warranty.
 # Sourced from http://bugs.debian.org/797228
 
 m4_define([_CHECK_ATOMIC_testbody], [[
-  #include <atomic>
-  #include <cstdint>
-  int main() {
-    std::atomic<int64_t> a{};
-    int64_t v = 5;
-    int64_t r = a.fetch_add(v);
-    return static_cast<int>(r);
-  }
+#include <atomic>
+#include <cstdint>
+
+template< typename T >
+struct Tagged
+{
+    T t;
+    uint32_t _tag;
+    static const int tag_bits = 16;
+    void tag( uint32_t v ) { _tag = v; }
+    uint32_t tag() { return _tag; }
+    Tagged() noexcept : t(), _tag( 0 ) {}
+    Tagged( const T &t ) : t( t ), _tag( 0 ) {}
+};
+
+int main() {
+  std::atomic<int64_t> a{};
+  int64_t v = 5;
+  int64_t r = a.fetch_add(v);
+  std::atomic<Tagged<int>> value;
+  return static_cast<int>(r) + value.load().t;
+}
 ]])
 
 AC_DEFUN([CHECK_ATOMIC], [