diff options
Diffstat (limited to 'gcc/doc/gty.texi')
| -rw-r--r-- | gcc/doc/gty.texi | 37 |
1 files changed, 29 insertions, 8 deletions
diff --git a/gcc/doc/gty.texi b/gcc/doc/gty.texi index 56da9b55fc9..05a279c7d7c 100644 --- a/gcc/doc/gty.texi +++ b/gcc/doc/gty.texi @@ -149,20 +149,17 @@ option is a fragment of C code that calculates the length. The second case is when a structure or a global variable contains a pointer to an array, like this: @smallexample -tree * - GTY ((length ("%h.regno_pointer_align_length"))) regno_decl; +struct gimple_omp_for_iter * GTY((length ("%h.collapse"))) iter; @end smallexample -In this case, @code{regno_decl} has been allocated by writing something like +In this case, @code{iter} has been allocated by writing something like @smallexample - x->regno_decl = - ggc_alloc (x->regno_pointer_align_length * sizeof (tree)); + x->iter = ggc_alloc_cleared_vec_gimple_omp_for_iter (collapse); @end smallexample -and the @code{length} provides the length of the field. +and the @code{collapse} provides the length of the field. This second use of @code{length} also works on global variables, like: @verbatim - static GTY((length ("reg_base_value_size"))) - rtx *reg_base_value; +static GTY((length("reg_known_value_size"))) rtx *reg_known_value; @end verbatim @findex skip @@ -353,6 +350,30 @@ of pointers. @code{reorder} functions can be expensive. When possible, it is better to depend on properties of the data, like an ID number or the hash of a string instead. +@findex variable_size +@item variable_size + +The type machinery expects the types to be of constant size. When this +is not true, for example, with structs that have array fields or unions, +the type machinery cannot tell how many bytes need to be allocated at +each allocation. The @code{variable_size} is used to mark such types. +The type machinery then provides allocators that take a parameter +indicating an exact size of object being allocated. + +For example, +@smallexample +struct GTY((variable_size)) sorted_fields_type @{ + int len; + tree GTY((length ("%h.len"))) elts[1]; +@}; +@end smallexample + +Then the objects of @code{struct sorted_fields_type} are allocated in GC +memory as follows: +@smallexample + field_vec = ggc_alloc_sorted_fields_type (size); +@end smallexample + @findex special @item special ("@var{name}") |