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| author | Richard Kenner <kenner@vlsi1.ultra.nyu.edu> | 2003-11-03 23:47:11 +0000 |
|---|---|---|
| committer | Richard Kenner <kenner@gcc.gnu.org> | 2003-11-03 18:47:11 -0500 |
| commit | aef6a62423341540cf979a2bb9c45e7463c097b1 (patch) | |
| tree | f329ecb8bce257457c0e34d06d9b1ca8c3b60696 | |
| parent | 930177d9f0ab0015f02f4961cda28ab63dfd468a (diff) | |
| download | gcc-aef6a62423341540cf979a2bb9c45e7463c097b1.zip gcc-aef6a62423341540cf979a2bb9c45e7463c097b1.tar.gz gcc-aef6a62423341540cf979a2bb9c45e7463c097b1.tar.bz2 | |
gty.texi (tag, desc): Say more about role of desc values in selecting between tags.
* doc/gty.texi (tag, desc): Say more about role of desc values in
selecting between tags.
From-SVN: r73233
| -rw-r--r-- | gcc/ChangeLog | 5 | ||||
| -rw-r--r-- | gcc/doc/gty.texi | 29 |
2 files changed, 23 insertions, 11 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 9aa90f6..268ed0c 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,8 @@ +2003-11-03 Richard Kenner <kenner@vlsi1.ultra.nyu.edu> + + * doc/gty.texi (tag, desc): Say more about role of desc values in + selecting between tags. + 2003-11-03 Alexander Kabaev <ak03@gte.com> * real.c (encode_ieee_single): Ensure proper promotion. diff --git a/gcc/doc/gty.texi b/gcc/doc/gty.texi index 6d4f839..56ce597 100644 --- a/gcc/doc/gty.texi +++ b/gcc/doc/gty.texi @@ -132,8 +132,19 @@ field really isn't ever used. @itemx default The type machinery needs to be told which field of a @code{union} is -currently active. This is done by giving each field a constant @code{tag} -value, and then specifying a discriminator using @code{desc}. For example, +currently active. This is done by giving each field a constant +@code{tag} value, and then specifying a discriminator using @code{desc}. +The value of the expression given by @code{desc} is compared against +each @code{tag} value, each of which should be different. If no +@code{tag} is matched, the field marked with @code{default} is used if +there is one, otherwise no field in the union will be marked. + +In the @code{desc} option, the ``current structure'' is the union that +it discriminates. Use @code{%1} to mean the structure containing it. +(There are no escapes available to the @code{tag} option, since it's +supposed to be a constant.) + +For example, @smallexample struct tree_binding GTY(()) @{ @@ -141,19 +152,15 @@ struct tree_binding GTY(()) union tree_binding_u @{ tree GTY ((tag ("0"))) scope; struct cp_binding_level * GTY ((tag ("1"))) level; - @} GTY ((desc ("BINDING_HAS_LEVEL_P ((tree)&%0)"))) scope; + @} GTY ((desc ("BINDING_HAS_LEVEL_P ((tree)&%0)"))) xscope; tree value; @}; @end smallexample -In the @code{desc} option, the ``current structure'' is the union that -it discriminates. Use @code{%1} to mean the structure containing it. -(There are no escapes available to the @code{tag} option, since it's -supposed to be a constant.) - -Each @code{tag} should be different. If no @code{tag} is matched, -the field marked with @code{default} is used if there is one, otherwise -no field in the union will be marked. +In this example, the value of BINDING_HAS_LEVEL_P when applied to a +@code{struct tree_binding *} is presumed to be 0 or 1. If 1, the type +mechanism will treat the field @code{level} as being present and if 0, +will treat the field @code{scope} as being present. @findex param_is @findex use_param |