[Bug tree-optimization/53852] [4.8 Regression] -ftree-loop-linear: large compile time / memory usage

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53852

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-13 12:59:45 UTC ---
Sven suggests sth like:

Index: gcc/graphite-dependences.c
===================================================================
--- gcc/graphite-dependences.c  (revision 194472)
+++ gcc/graphite-dependences.c  (working copy)
@@ -461,13 +461,16 @@ compute_deps (scop_p scop, vec<poly_bb_p
   isl_union_map *reads = scop_get_reads (scop, pbbs);
   isl_union_map *must_writes = scop_get_must_writes (scop, pbbs);
   isl_union_map *may_writes = scop_get_may_writes (scop, pbbs);
-  isl_union_map *all_writes = isl_union_map_union
-    (isl_union_map_copy (must_writes), isl_union_map_copy (may_writes));
-  isl_space *space = isl_union_map_get_space (all_writes);
-  isl_union_map *empty = isl_union_map_empty (space);
   isl_union_map *original = scop_get_original_schedule (scop, pbbs);
   int res;

+  reads = isl_union_map_coalesce (reads);
+  must_writes = isl_union_map_coalesce (must_writes);
+  may_writes = isl_union_map_coalesce (may_writes);
+  isl_union_map *all_writes = isl_union_map_union
+    (isl_union_map_copy (must_writes), isl_union_map_copy (may_writes));
+  all_writes = isl_union_map_coalesce (all_writes);
+  original = isl_union_map_coalesce (original);
   res = isl_union_map_compute_flow (isl_union_map_copy (reads),
                                    isl_union_map_copy (must_writes),
                                    isl_union_map_copy (may_writes),
@@ -475,6 +478,8 @@ compute_deps (scop_p scop, vec<poly_bb_p
                                    must_raw, may_raw, must_raw_no_source,
                                    may_raw_no_source);
   gcc_assert (res == 0);
+  isl_space *space = isl_union_map_get_space (all_writes);
+  isl_union_map *empty = isl_union_map_empty (space);
   res = isl_union_map_compute_flow (isl_union_map_copy (all_writes),
                                    reads, empty,
                                    isl_union_map_copy (original),

which for me only shaves a small bit of compile-time from the reduced testcase
(around 10%).