gc-alloc 0.2.1

A Rust library for garbage-collected memory allocation using libgc (bdwgc).
Documentation 
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/*
 * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 1999-2003 by Hewlett-Packard Company. All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

#if !defined(AO_ATOMIC_OPS_H) || defined(AO_ATOMIC_OPS_INCLUDED)
# error This file should not be included directly.
#endif

#if (AO_GNUC_PREREQ(5, 4) || AO_CLANG_PREREQ(8, 0)) && defined(__s390x__) \
    && !defined(AO_DISABLE_GCC_ATOMICS)
  /* Probably, it could be enabled for earlier clang/gcc versions.      */
  /* But, e.g., clang-3.8.0 produces a backend error for AtomicFence.   */

# include "generic.h"

#else /* AO_DISABLE_GCC_ATOMICS */

/* The relevant documentation appears to be in                  */
/* "z/Architecture Principles of Operation" book                */
/* (https://publibfp.dhe.ibm.com/epubs/pdf/a227832c.pdf).       */
/* Apparently:                                                  */
/* - Memory references in general are atomic only for a single  */
/*   byte.  But it appears that the most common load/store      */
/*   instructions also guarantee atomicity for aligned          */
/*   operands of standard types.  WE FOOLISHLY ASSUME that      */
/*   compilers only generate those.  If that turns out to be    */
/*   wrong, we need inline assembly code for AO_load and        */
/*   AO_store.                                                  */
/* - A store followed by a load is unordered since the store    */
/*   may be delayed.  Otherwise everything is ordered.          */
/* - There is a hardware compare-and-swap (CS) instruction.     */

#include "../all_aligned_atomic_load_store.h"

#include "../ordered_except_wr.h"

#include "../test_and_set_t_is_ao_t.h"
/* TODO: Is there a way to do byte-sized test-and-set? */

/* TODO: AO_nop_full should probably be implemented directly.   */
/* It appears that certain BCR instructions have that effect.   */
/* Presumably they're cheaper than CS?                          */

#ifndef AO_GENERALIZE_ASM_BOOL_CAS
AO_INLINE int AO_compare_and_swap_full(volatile AO_t *addr,
                                       AO_t old, AO_t new_val)
{
  int retval;
  __asm__ __volatile__ (
# ifndef __s390x__
    "     cs  %1,%2,0(%3)\n"
# else
    "     csg %1,%2,0(%3)\n"
# endif
  "     ipm %0\n"
  "     srl %0,28\n"
  : "=&d" (retval), "+d" (old)
  : "d" (new_val), "a" (addr)
  : "cc", "memory");
  return retval == 0;
}
#define AO_HAVE_compare_and_swap_full
#endif /* !AO_GENERALIZE_ASM_BOOL_CAS */

AO_INLINE AO_t
AO_fetch_compare_and_swap_full(volatile AO_t *addr,
                               AO_t old, AO_t new_val)
{
  __asm__ __volatile__ (
#   ifndef __s390x__
      "     cs %0,%2,%1\n"
#   else
      "     csg %0,%2,%1\n"
#   endif
    : "+d" (old), "=Q" (*addr)
    : "d" (new_val), "m" (*addr)
    : "cc", "memory");
  return old;
}
#define AO_HAVE_fetch_compare_and_swap_full

#endif /* AO_DISABLE_GCC_ATOMICS */

/* TODO: Add double-wide operations for 32-bit executables.       */