Add TARGET_COMPUTE_MULTILIB hook to override multi-lib result.

Create a new hook to let target could override the multi-lib result,
the motivation is RISC-V might have very complicated multi-lib re-use
rule*, which is hard to maintain and use current multi-lib scripts,
we even hit the "argument list too long" error when we tried to add more
multi-lib reuse rule.

So I think it would be great to have a target specific way to determine
the multi-lib re-use rule, then we could write those rule in C, instead
of expand every possible case in MULTILIB_REUSE.

* Here is an example for RISC-V multi-lib rules:
https://gist.github.com/kito-cheng/0289cd42d9a756382e5afeb77b42b73b

gcc/ChangeLog:

	* common/common-target.def (compute_multilib): New.
	* common/common-targhooks.h (default_compute_multilib): New.
	* common/common-targhooks.cc (default_compute_multilib): New.
	* doc/tm.texi.in (TARGET_COMPUTE_MULTILIB): New.
	* doc/tm.texi: Regen.
	* gcc.cc: Include common/common-target.h.
	(set_multilib_dir) Call targetm_common.compute_multilib.
	(SWITCH_LIVE): Move to opts.h.
	(SWITCH_FALSE): Ditto.
	(SWITCH_IGNORE): Ditto.
	(SWITCH_IGNORE_PERMANENTLY): Ditto.
	(SWITCH_KEEP_FOR_GCC): Ditto.
	(struct switchstr): Ditto.
	* opts.h (SWITCH_LIVE): Move from gcc.c.
	(SWITCH_FALSE): Ditto.
	(SWITCH_IGNORE): Ditto.
	(SWITCH_IGNORE_PERMANENTLY): Ditto.
	(SWITCH_KEEP_FOR_GCC): Ditto.
	(struct switchstr): Ditto.

1 files changed, 36 insertions, 0 deletions

diff --git a/gcc/opts.h b/gcc/opts.h
index 73a96f3..ce4fd5c 100644
--- a/gcc/opts.h
+++ b/gcc/opts.h
@@ -527,4 +527,40 @@ extern char *gen_producer_string (const char *language_string,
 
 #define OPTION_SET_P(OPTION) global_options_set.x_ ## OPTION
 
+/* Find all the switches given to us
+   and make a vector describing them.
+   The elements of the vector are strings, one per switch given.
+   If a switch uses following arguments, then the `part1' field
+   is the switch itself and the `args' field
+   is a null-terminated vector containing the following arguments.
+   Bits in the `live_cond' field are:
+   SWITCH_LIVE to indicate this switch is true in a conditional spec.
+   SWITCH_FALSE to indicate this switch is overridden by a later switch.
+   SWITCH_IGNORE to indicate this switch should be ignored (used in %<S).
+   SWITCH_IGNORE_PERMANENTLY to indicate this switch should be ignored.
+   SWITCH_KEEP_FOR_GCC to indicate that this switch, otherwise ignored,
+   should be included in COLLECT_GCC_OPTIONS.
+   in all do_spec calls afterwards.  Used for %<S from self specs.
+   The `known' field describes whether this is an internal switch.
+   The `validated' field describes whether any spec has looked at this switch;
+   if it remains false at the end of the run, the switch must be meaningless.
+   The `ordering' field is used to temporarily mark switches that have to be
+   kept in a specific order.  */
+
+#define SWITCH_LIVE    			(1 << 0)
+#define SWITCH_FALSE   			(1 << 1)
+#define SWITCH_IGNORE			(1 << 2)
+#define SWITCH_IGNORE_PERMANENTLY	(1 << 3)
+#define SWITCH_KEEP_FOR_GCC		(1 << 4)
+
+struct switchstr
+{
+  const char *part1;
+  const char **args;
+  unsigned int live_cond;
+  bool known;
+  bool validated;
+  bool ordering;
+};
+
 #endif