[PATCH] Speedup lookup_constraint for 2-letter constraints

[Richard Biener]

This speeds up lookup_constraint by allowing the generic folding
for n == 1 strncmp calls to trigger, handling two-letter constraints
by two char comparisons instead of one and a call to strncmp (which
ends up not being inlined because it's considered cold ...).

Bootstrap & regtest pending on x86_64-unknown-linux-gnu.

Ok?

Thanks,
Richard.
2013-02-19  Richard Biener  <rguent...@suse.de>

        * genpreds.c (write_lookup_constraint): Do not compare first
        letter of the constraint again.

Index: gcc/genpreds.c
===================================================================
--- gcc/genpreds.c      (revision 196134)
+++ gcc/genpreds.c      (working copy)
@@ -945,9 +945,10 @@ write_lookup_constraint (void)
        {
          do
            {
-             printf ("      if (!strncmp (str, \"%s\", %lu))\n"
+             printf ("      if (!strncmp (str + 1, \"%s\", %lu))\n"
                      "        return CONSTRAINT_%s;\n",
-                     c->name, (unsigned long int) c->namelen, c->c_name);
+                     c->name + 1, (unsigned long int) c->namelen - 1,
+                     c->c_name);
              c = c->next_this_letter;
            }
          while (c);