Re: c++/10112: static data member is not correctly initialised

["Giovanni Bajo" <giovannibajo@libero.it>]

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The following reply was made to PR c++/10112; it has been noted by GNATS.

From: "Giovanni Bajo" <giovannibajo@libero.it>
To: <gcc-gnats@gcc.gnu.org>,
	<gcc-bugs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>,
	<O.Kullmann@Swansea.ac.uk>,
	<gcc-prs@gcc.gnu.org>
Cc:  
Subject: Re: c++/10112: static data member is not correctly initialised
Date: Sun, 16 Mar 2003 23:22:30 +0100

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&p
 r=10112
 
 Confirmed with 3.2, cygwin on x86. Reduced snippet is:
 
 ----------------------------------
 #include <cassert>
 using namespace std;
 
 struct A
 {
  int p;
 
  A(int _p) : p(_p)
  {}
 };
 
 template <typename T>
 struct B
 {
   static A a;
   static int p1;
 };
 
 
 template <typename T> A B<T>::a(123);
 template <typename T> int B<T>::p1 = a.p;
 
 int main()
 {
  // Should not assert, but it does
  assert(B<int>::p1 == B<int>::a.p);
 }
 ----------------------------------
 
 Looking at the generated code on x86, it seems that the two variables are
 initialized in reversed order:
 
 00401104 <__Z41__static_initialization_and_destruction_0ii>:
     [....]
   401139: a1 b0 e8 40 00        mov    0x40e8b0,%eax
   40113e: a3 a0 e8 40 00        mov    %eax,0x40e8a0
     [....]
   401172: c7 04 24 b0 e8 40 00  movl   $0x40e8b0,(%esp,1)
   401179: c7 44 24 04 7b 00 00  movl   $0x7b,0x4(%esp,1)
   401180: 00
   401181: e8 9a 47 00 00        call   405920 <__ZN1AC1Ei>
 
 00405920 <__ZN1AC1Ei>:
   405920: 55                    push   %ebp
   405921: 89 e5                 mov    %esp,%ebp
   405923: 8b 55 08              mov    0x8(%ebp),%edx
   405926: 8b 45 0c              mov    0xc(%ebp),%eax
   405929: 89 02                 mov    %eax,(%edx)
   40592b: 5d                    pop    %ebp
   40592c: c3                    ret
 
 
 The code at 401139 copies B<T>::a.p into B<T>::p1 (it's the initialization
 of B<T>::p1), while the second block initializes B<T>::a.p with 123 (0x7b),
 but it's too late. I tried with no optimization, and -O0/1/2/3 and there is
 no difference, the code is always wrong.
 
 As for the standard, §9.4.2p7 says <<Static data members are initialized and
 destroyed exactly like nonlocal objects (3.6.2, 3.6.3).>>. §3.6.2p1 says:
 <<Objects of POD types (3.9) with static storage duration initialized with
 constant expressions (5.19) shall be initialized before any dynamic
 initialization takes place. Objects with static storage duration defined in
 namespace scope in the same translation unit and dynamically initialized
 shall be initialized in the order in which their definition appears in the
 translation unit.>>. Now, B<T>::p1 is a POD type but it is not initialized
 with a constant expression, so I don't see any reason why it should be
 initialized before B<T>::a.
 
 Giovanni Bajo