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Re: RFA: GCC 4.2.1: Stabalizing coalesce_list's qsort
Hi Richard,
Since stabilizing the sort would slow it down, I thought it best to check to
make sure that it is still OK to apply the patch. ie are we preferring host
independence over compile speed ?
Yes. I don't think the slowdown will be noticable.
OK, I have checked in the attached version of the patch.
Cheers
Nick
gcc/ChangeLog
2007-08-31 Nick Clifton <nickc@redhat.com>
* tree-ssa-coalesce.c (compare_pairs): Use the elements as
secondary keys in order to obtain a stable sort.
Index: gcc/tree-ssa-coalesce.c
===================================================================
--- gcc/tree-ssa-coalesce.c (revision 127921)
+++ gcc/tree-ssa-coalesce.c (working copy)
@@ -314,8 +314,22 @@ add_coalesce (coalesce_list_p cl, int p1
static int
compare_pairs (const void *p1, const void *p2)
{
- return (*(const_coalesce_pair_p const*)p1)->cost
- - (*(const_coalesce_pair_p const*)p2)->cost;
+ const_coalesce_pair_p const * pp1 = p1;
+ const_coalesce_pair_p const * pp2 = p2;
+ int result;
+
+ result = (* pp2)->cost - (* pp1)->cost;
+ /* Since qsort does not guarantee stability we use the elements
+ as a secondary key. This provides us with independence from
+ the host's implementation of the sorting algorithm. */
+ if (result == 0)
+ {
+ result = (* pp2)->first_element - (* pp1)->first_element;
+ if (result == 0)
+ result = (* pp2)->second_element - (* pp1)->second_element;
+ }
+
+ return result;
}