Fix genmultilib reuse rule checks for large sets of option combinations

[Joseph Myers <joseph@codesourcery.com>]

genmultilib computes combination_space, a list of all combinations of
options in MULTILIB_OPTIONS that might have multilibs built for them
(some of which may end up not having multilibs built for them, and
some of those may end up being mapped to other multilibs with
MULTILIB_REUSE).  It is then used to validate the right hand part of
MULTILIB_REUSE rules, checking with expr that combination_space
matches a basic regular expression derived from that right hand part.

There are two problems with this approach to validation:

* It requires that right hand part to have options in the same order
  as in MULTILIB_OPTIONS, in contradiction to the documentation of
  MULTILIB_REUSE saying that order does not matter there.

* combination_space can be so large that the expr call fails with an
  E2BIG error.  I have a local ARM configuration with 40 multilibs but
  3840 combinations of options from MULTILIB_OPTIONS (so 3839 listed
  in combination_space, since it doesn't list the default multilib)
  and 996 MULTILIB_REUSE rules.  This generates a combination_space
  string longer than the Linux kernel's MAX_ARG_STRLEN (PAGE_SIZE *
  32, the limit on the length of a single argv string), so that expr
  cannot be run.

This patch changes the validation approach to generate a much shorter
extended regular expression for any sequence of multilib options in
any order, and uses that for the validation instead.

Tested with a built for arm-none-eabi --with-multilib-list=aprofile
(as a configuration that uses MULTILIB_REUSE).

2017-06-08  Joseph Myers  <joseph@codesourcery.com>

	* genmultilib (combination_space): Remove variable.
	Validate reuse rules against regular expression for any sequence
	of multilib options in any order.

Index: gcc/genmultilib
===================================================================
--- gcc/genmultilib	(revision 249028)
+++ gcc/genmultilib	(working copy)
@@ -186,8 +186,7 @@
 EOF
 chmod +x tmpmultilib
 
-combination_space=`initial=/ ./tmpmultilib ${options}`
-combinations="$combination_space"
+combinations=`initial=/ ./tmpmultilib ${options}`
 
 # If there exceptions, weed them out now
 if [ -n "${exceptions}" ]; then
@@ -460,6 +459,15 @@
 echo "NULL"
 echo "};"
 
+# Generate a regular expression to validate option combinations.
+options_re=
+for set in ${options}; do
+  for opt in `echo ${set} | sed -e 's_[/|]_ _g'`; do
+    options_re="${options_re}${options_re:+|}${opt}"
+  done
+done
+options_re="^/((${options_re})/)*\$"
+
 # Output rules used for multilib reuse.
 echo ""
 echo "static const char *const multilib_reuse_raw[] = {"
@@ -473,7 +481,7 @@
   # in this variable, it means no multilib will be built for current reuse
   # rule.  Thus the reuse purpose specified by current rule is meaningless.
   if expr "${combinations} " : ".*/${combo}/.*" > /dev/null; then
-    if expr "${combination_space} " : ".*/${copts}/.*" > /dev/null; then
+    if echo "/${copts}/" | grep -E "${options_re}" > /dev/null; then
       combo="/${combo}/"
       dirout=`./tmpmultilib3 "${combo}" "${todirnames}" "${toosdirnames}" "${enable_multilib}"`
       copts="/${copts}/"

-- 
Joseph S. Myers
joseph@codesourcery.com