diff options
Diffstat (limited to 'libguile/gc.h')
-rw-r--r-- | libguile/gc.h | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/libguile/gc.h b/libguile/gc.h index f53981b6f..9f00e017b 100644 --- a/libguile/gc.h +++ b/libguile/gc.h @@ -218,6 +218,103 @@ SCM_API char *scm_gc_strndup (const char *str, size_t n, const char *what) #endif +SCM_INLINE SCM scm_cell (scm_t_bits car, scm_t_bits cdr); +SCM_INLINE SCM scm_double_cell (scm_t_bits car, scm_t_bits cbr, + scm_t_bits ccr, scm_t_bits cdr); +SCM_INLINE SCM scm_words (scm_t_bits car, scm_t_uint16 n_words); + +#if SCM_CAN_INLINE || defined SCM_INLINE_C_IMPLEMENTING_INLINES + +SCM_INLINE_IMPLEMENTATION SCM +scm_cell (scm_t_bits car, scm_t_bits cdr) +{ + SCM cell = PTR2SCM (SCM_GC_MALLOC (sizeof (scm_t_cell))); + + /* Initialize the type slot last so that the cell is ignored by the GC + until it is completely initialized. This is only relevant when the GC + can actually run during this code, which it can't since the GC only runs + when all other threads are stopped. */ + SCM_GC_SET_CELL_WORD (cell, 1, cdr); + SCM_GC_SET_CELL_WORD (cell, 0, car); + + return cell; +} + +SCM_INLINE_IMPLEMENTATION SCM +scm_double_cell (scm_t_bits car, scm_t_bits cbr, + scm_t_bits ccr, scm_t_bits cdr) +{ + SCM z; + + z = PTR2SCM (SCM_GC_MALLOC (2 * sizeof (scm_t_cell))); + /* Initialize the type slot last so that the cell is ignored by the + GC until it is completely initialized. This is only relevant + when the GC can actually run during this code, which it can't + since the GC only runs when all other threads are stopped. + */ + SCM_GC_SET_CELL_WORD (z, 1, cbr); + SCM_GC_SET_CELL_WORD (z, 2, ccr); + SCM_GC_SET_CELL_WORD (z, 3, cdr); + SCM_GC_SET_CELL_WORD (z, 0, car); + + /* When this function is inlined, it's possible that the last + SCM_GC_SET_CELL_WORD above will be adjacent to a following + initialization of z. E.g., it occurred in scm_make_real. GCC + from around version 3 (e.g., certainly 3.2) began taking + advantage of strict C aliasing rules which say that it's OK to + interchange the initialization above and the one below when the + pointer types appear to differ sufficiently. We don't want that, + of course. GCC allows this behaviour to be disabled with the + -fno-strict-aliasing option, but would also need to be supplied + by Guile users. Instead, the following statements prevent the + reordering. + */ +#ifdef __GNUC__ + __asm__ volatile ("" : : : "memory"); +#else + /* portable version, just in case any other compiler does the same + thing. */ + scm_remember_upto_here_1 (z); +#endif + + return z; +} + +SCM_INLINE_IMPLEMENTATION SCM +scm_words (scm_t_bits car, scm_t_uint16 n_words) +{ + SCM z; + + z = PTR2SCM (SCM_GC_MALLOC (sizeof (scm_t_bits) * n_words)); + SCM_GC_SET_CELL_WORD (z, 0, car); + + /* FIXME: is the following concern even relevant with BDW-GC? */ + + /* When this function is inlined, it's possible that the last + SCM_GC_SET_CELL_WORD above will be adjacent to a following + initialization of z. E.g., it occurred in scm_make_real. GCC + from around version 3 (e.g., certainly 3.2) began taking + advantage of strict C aliasing rules which say that it's OK to + interchange the initialization above and the one below when the + pointer types appear to differ sufficiently. We don't want that, + of course. GCC allows this behaviour to be disabled with the + -fno-strict-aliasing option, but would also need to be supplied + by Guile users. Instead, the following statements prevent the + reordering. + */ +#ifdef __GNUC__ + __asm__ volatile ("" : : : "memory"); +#else + /* portable version, just in case any other compiler does the same + thing. */ + scm_remember_upto_here_1 (z); +#endif + + return z; +} + +#endif /* SCM_CAN_INLINE || defined SCM_INLINE_C_IMPLEMENTING_INLINES */ + SCM_API void scm_remember_upto_here_1 (SCM obj); SCM_API void scm_remember_upto_here_2 (SCM obj1, SCM obj2); SCM_API void scm_remember_upto_here (SCM obj1, ...); |