resolve libstdc++/5198

[Richard Henderson <rth at redhat dot com>]

Tested by building m68k-elf with all multilibs.

The patch Aaron Grier presents near the end of the PR history
isn't quite right.  First, 68000 did have TAS; it's only 5200/5300
that don't have that.  Second, the external lock variable for TAS
needs special care.  I patterned this off the sparc port which
needs the same thing.

Also, I don't see anything in the moto docs that require addl
with a memory destination to be atomic.  It may well be that it
is on certain implementations, but I don't know which for sure.
So make it use the known atomic __exchange_and_add and let the
compiler throw away the result.

Committed.


r~


        PR libstdc++/5198
        * config/cpu/m68k/bits/atomicity.h (__exchange_and_add): Only use
        CAS on the cpu variants that support it.  Add versions that use
        TAS and that disable interrupts.
        (__atomic_add): Use __exchange_and_add to guarantee atomicity.

Index: config/cpu/m68k/bits/atomicity.h
===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/config/cpu/m68k/bits/atomicity.h,v
retrieving revision 1.2
diff -c -p -d -r1.2 atomicity.h
*** atomicity.h	2001/08/15 16:00:45	1.2
--- atomicity.h	2002/01/24 01:23:54
***************
*** 1,6 ****
! // Low-level functions for atomic operations: m680x0, x >= 2 version -*- C++ -*-
  
! // Copyright (C) 2001 Free Software Foundation, Inc.
  //
  // This file is part of the GNU ISO C++ Library.  This library is free
  // software; you can redistribute it and/or modify it under the
--- 1,6 ----
! // Low-level functions for atomic operations: m68k version -*- C++ -*-
  
! // Copyright (C) 2001, 2002 Free Software Foundation, Inc.
  //
  // This file is part of the GNU ISO C++ Library.  This library is free
  // software; you can redistribute it and/or modify it under the
***************
*** 32,61 ****
  
  typedef int _Atomic_word;
  
  static inline _Atomic_word 
  __attribute__ ((__unused__))
  __exchange_and_add (volatile _Atomic_word *__mem, int __val)
  {
    register _Atomic_word __result = *__mem;
    register _Atomic_word __temp;
!   __asm__ __volatile__ ("1: move%.l %0,%1;"
! 			"   add%.l %2,%1;"
! 			"   cas%.l %0,%1,%3;"
! 			"   jbne 1b"
  			: "=d" (__result), "=&d" (__temp)
  			: "d" (__val), "m" (*__mem), "0" (__result)
  			: "memory");
    return __result;
  }
  
  static inline void
  __attribute__ ((__unused__))
  __atomic_add (volatile _Atomic_word* __mem, int __val)
  {
!   __asm__ __volatile__ ("add%.l %0,%1"
! 			: : "id" (__val), "m" (*__mem) : "memory");
  }
  
  #endif /* atomicity.h */
- 
- 
--- 32,136 ----
  
  typedef int _Atomic_word;
  
+ #if defined(__mc68020__) || defined(__mc68030__) \
+     || defined(__mc68040__) || defined(__mc68060__)
+ // These variants support compare-and-swap.
+ 
  static inline _Atomic_word 
  __attribute__ ((__unused__))
  __exchange_and_add (volatile _Atomic_word *__mem, int __val)
  {
    register _Atomic_word __result = *__mem;
    register _Atomic_word __temp;
!   __asm__ __volatile__ ("1: move%.l %0,%1\n\t"
! 			"add%.l %2,%1\n\t"
! 			"cas%.l %0,%1,%3\n\t"
! 			"jbne 1b"
  			: "=d" (__result), "=&d" (__temp)
  			: "d" (__val), "m" (*__mem), "0" (__result)
  			: "memory");
    return __result;
  }
  
+ #elif !defined(__mcf5200__) && !defined(__mcf5300__)
+ // 68000, 68010, cpu32 and 5400 support test-and-set.
+ 
+ template <int __inst>
+ struct __Atomicity_lock
+ {
+   static volatile unsigned char _S_atomicity_lock;
+ };
+ 
+ template <int __inst>
+ volatile unsigned char __Atomicity_lock<__inst>::_S_atomicity_lock = 0;
+ 
+ template volatile unsigned char __Atomicity_lock<0>::_S_atomicity_lock;
+ 
+ static inline _Atomic_word 
+ __attribute__ ((__unused__))
+ __exchange_and_add (volatile _Atomic_word *__mem, int __val)
+ {
+   _Atomic_word __result;
+ 
+   __asm__ __volatile__("1: tas %0\n\tjbne 1b"
+ 		       : "=m"(__Atomicity_lock<0>::_S_atomicity_lock)
+ 		       : "m"(__Atomicity_lock<0>::_S_atomicity_lock));
+ 
+   __result = *__mem;
+   *__mem = __result + __val;
+ 
+   __Atomicity_lock<0>::_S_atomicity_lock = 0;
+ 
+   return __result;
+ }
+ 
+ #else
+ // These variants do not support any atomic operations at all.
+ // The best we can hope for is to disable interrupts, which we
+ // can only do from supervisor mode.
+ 
+ #if defined(__rtems__) || defined(__vxWorks__) || defined(__embedded__)
+ static inline _Atomic_word 
+ __attribute__ ((__unused__))
+ __exchange_and_add (volatile _Atomic_word *__mem, int __val)
+ {
+   _Atomic_word __result;
+   short __level, __tmpsr;
+   __asm__ __volatile__ ("move%.w %%sr,%0\n\tor%.l %0,%1\n\tmove%.w %1,%%sr"
+ 		  	: "=d"(__level), "=d"(__tmpsr) : "1"(0x700));
+ 
+   __result = *__mem;
+   *__mem = __result + __val;
+ 
+   __asm__ __volatile__ ("move%.w %0,%%sr" : : "d"(__level));
+ 
+   return __result;
+ }
+ #else
+ #warning "__exchange_and_add is not atomic for this target"
+ 
+ static inline _Atomic_word
+ __attribute__ ((__unused__))
+ __exchange_and_add (volatile _Atomic_word *__mem, int __val)
+ {
+   _Atomic_word __result;
+ 
+   __result = *__mem;
+   *__mem = __result + __val;
+ 
+   return __result;
+ }
+ 
+ #endif /* embedded */
+ #endif /* CAS / TAS / IRQ */
+ 
  static inline void
  __attribute__ ((__unused__))
  __atomic_add (volatile _Atomic_word* __mem, int __val)
  {
!   // Careful: using add.l with a memory destination is not
!   // architecturally guaranteed to be atomic.
!   (void) __exchange_and_add (__mem, __val);
  }
  
  #endif /* atomicity.h */