X-Git-Url: http://review.tizen.org/git/?a=blobdiff_plain;f=isl_tab_pip.c;h=2592a285c0e179164254439f4b2c0e0d84bd12ed;hb=da1dc20cb7aa4509e375f703c35beaf27dfa4a15;hp=d5ed6548e9deed050deb9e484ee6de30588074f1;hpb=07bca32eef20102a070cc4c8d6a86f1aa8d8560e;p=platform%2Fupstream%2Fisl.git

diff --git a/isl_tab_pip.c b/isl_tab_pip.c
index d5ed654..2592a28 100644
--- a/isl_tab_pip.c
+++ b/isl_tab_pip.c
@@ -124,6 +124,8 @@ struct isl_context_lex {
  * "M" describes the solution in terms of the dimensions of "dom".
  * The number of columns of "M" is one more than the total number
  * of dimensions of "dom".
+ *
+ * If "M" is NULL, then there is no solution on "dom".
  */
 struct isl_partial_sol {
 	int level;
@@ -322,11 +324,15 @@ static void sol_pop(struct isl_sol *sol)
 			isl_basic_set_free(partial->next->dom);
 			partial->next->dom = bset;
 			M = partial->next->M;
-			M = isl_mat_drop_cols(M, M->n_col - n, n);
-			partial->next->M = M;
+			if (M) {
+				M = isl_mat_drop_cols(M, M->n_col - n, n);
+				partial->next->M = M;
+				if (!M)
+					goto error;
+			}
 			partial->next->level = sol->level;
 
-			if (!bset || !M)
+			if (!bset)
 				goto error;
 
 			sol->partial = partial->next;
@@ -3870,6 +3876,24 @@ error:
 	sol->error = 1;
 }
 
+/* Does "sol" contain a pair of partial solutions that could potentially
+ * be merged?
+ *
+ * We currently only check that "sol" is not in an error state
+ * and that there are at least two partial solutions of which the final two
+ * are defined at the same level.
+ */
+static int sol_has_mergeable_solutions(struct isl_sol *sol)
+{
+	if (sol->error)
+		return 0;
+	if (!sol->partial)
+		return 0;
+	if (!sol->partial->next)
+		return 0;
+	return sol->partial->level == sol->partial->next->level;
+}
+
 /* Compute the lexicographic minimum of the set represented by the main
  * tableau "tab" within the context "sol->context_tab".
  *
@@ -3880,10 +3904,20 @@ error:
  * corresponding rows may not be marked as being non-negative.
  * In parts of the context where the added equality does not hold,
  * the main tableau is marked as being empty.
+ *
+ * Before we embark on the actual computation, we save a copy
+ * of the context.  When we return, we check if there are any
+ * partial solutions that can potentially be merged.  If so,
+ * we perform a rollback to the initial state of the context.
+ * The merging of partial solutions happens inside calls to
+ * sol_dec_level that are pushed onto the undo stack of the context.
+ * If there are no partial solutions that can potentially be merged
+ * then the rollback is skipped as it would just be wasted effort.
  */
 static void find_solutions_main(struct isl_sol *sol, struct isl_tab *tab)
 {
 	int row;
+	void *saved;
 
 	if (!tab)
 		goto error;
@@ -3933,8 +3967,15 @@ static void find_solutions_main(struct isl_sol *sol, struct isl_tab *tab)
 		row = tab->n_redundant - 1;
 	}
 
+	saved = sol->context->op->save(sol->context);
+
 	find_solutions(sol, tab);
 
+	if (sol_has_mergeable_solutions(sol))
+		sol->context->op->restore(sol->context, saved);
+	else
+		sol->context->op->discard(saved);
+
 	sol->level = 0;
 	sol_pop(sol);