From: Sven Verdoolaege <skimo@kotnet.org>
Date: Fri, 22 May 2009 09:26:31 +0000 (+0200)
Subject: isl_map_compute_divs: drop obviously redundant divs first
X-Git-Tag: isl-0.01~169
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=d96a3a8e3534fb91c89516ab01eeea06af15b3ba;hp=7635ee8ae7ea70cef81e389155ef7e1694af0c09;p=platform%2Fupstream%2Fisl.git

isl_map_compute_divs: drop obviously redundant divs first
---

diff --git a/isl_map.c b/isl_map.c
index d23c30e..3f84e07 100644
--- a/isl_map.c
+++ b/isl_map.c
@@ -2944,6 +2944,11 @@ error:
 	return NULL;
 }
 
+/* If bmap contains any unknown divs, then compute explicit
+ * expressions for them.  However, this computation may be
+ * quite expensive, so first try to remove divs that aren't
+ * strictly needed.
+ */
 struct isl_map *isl_basic_map_compute_divs(struct isl_basic_map *bmap)
 {
 	int i;
@@ -2954,11 +2959,22 @@ struct isl_map *isl_basic_map_compute_divs(struct isl_basic_map *bmap)
 	off = isl_dim_total(bmap->dim);
 	for (i = 0; i < bmap->n_div; ++i) {
 		if (isl_int_is_zero(bmap->div[i][0]))
-			return isl_pip_basic_map_compute_divs(bmap);
+			break;
 		isl_assert(bmap->ctx, isl_int_is_zero(bmap->div[i][1+1+off+i]),
 				goto error);
 	}
-	return isl_map_from_basic_map(bmap);
+	if (i == bmap->n_div)
+		return isl_map_from_basic_map(bmap);
+	bmap = isl_basic_map_drop_redundant_divs(bmap);
+	if (!bmap)
+		goto error;
+	for (i = 0; i < bmap->n_div; ++i)
+		if (isl_int_is_zero(bmap->div[i][0]))
+			break;
+	if (i == bmap->n_div)
+		return isl_map_from_basic_map(bmap);
+	struct isl_map *map = isl_pip_basic_map_compute_divs(bmap);
+	return map;
 error:
 	isl_basic_map_free(bmap);
 	return NULL;
diff --git a/isl_map_private.h b/isl_map_private.h
index 3ef8dbf..de112b4 100644
--- a/isl_map_private.h
+++ b/isl_map_private.h
@@ -106,3 +106,6 @@ struct isl_basic_set *isl_basic_set_eliminate_vars(
 
 int isl_basic_set_constraint_is_redundant(struct isl_basic_set **bset,
 	isl_int *c, isl_int *opt_n, isl_int *opt_d);
+
+struct isl_basic_map *isl_basic_map_drop_redundant_divs(
+	struct isl_basic_map *bmap);
diff --git a/isl_map_simplify.c b/isl_map_simplify.c
index d43f609..1a4bfa2 100644
--- a/isl_map_simplify.c
+++ b/isl_map_simplify.c
@@ -1855,3 +1855,91 @@ int isl_set_fast_is_disjoint(struct isl_set *set1, struct isl_set *set2)
 	return isl_map_fast_is_disjoint((struct isl_map *)set1,
 					(struct isl_map *)set2);
 }
+
+/* Remove divs that are not strictly needed.
+ * In particular, if a div only occurs positively (or negatively)
+ * in constraints, then it can simply be dropped.
+ * Also, if a div occurs only occurs in two constraints and if moreover
+ * those two constraints are opposite to each other, except for the constant
+ * term and if the sum of the constant terms is such that for any value
+ * of the other values, there is always at least one integer value of the
+ * div, i.e., if one plus this sum is greater than or equal to
+ * the (absolute value) of the coefficent of the div in the constraints,
+ * then we can also simply drop the div.
+ */
+struct isl_basic_map *isl_basic_map_drop_redundant_divs(
+	struct isl_basic_map *bmap)
+{
+	int i, j;
+	unsigned off;
+
+	if (!bmap)
+		goto error;
+
+	off = isl_dim_total(bmap->dim);
+
+	for (i = 0; i < bmap->n_div; ++i) {
+		int pos, neg;
+		int last_pos, last_neg;
+		int redundant;
+
+		if (!isl_int_is_zero(bmap->div[i][0]))
+			continue;
+		for (j = 0; j < bmap->n_eq; ++j)
+			if (!isl_int_is_zero(bmap->eq[j][1 + off + i]))
+				break;
+		if (j < bmap->n_eq)
+			continue;
+		pos = neg = 0;
+		for (j = 0; j < bmap->n_ineq; ++j) {
+			if (isl_int_is_pos(bmap->ineq[j][1 + off + i])) {
+				last_pos = j;
+				++pos;
+			}
+			if (isl_int_is_neg(bmap->ineq[j][1 + off + i])) {
+				last_neg = j;
+				++neg;
+			}
+		}
+		if (pos * neg == 0) {
+			for (j = bmap->n_ineq - 1; j >= 0; --j)
+				if (!isl_int_is_zero(bmap->ineq[j][1+off+i]))
+					isl_basic_map_drop_inequality(bmap, j);
+			bmap = isl_basic_map_drop_div(bmap, i);
+			return isl_basic_map_drop_redundant_divs(bmap);
+		}
+		if (pos * neg != 1)
+			continue;
+		if (!isl_seq_is_neg(bmap->ineq[last_pos] + 1,
+				    bmap->ineq[last_neg] + 1,
+				    off + bmap->n_div))
+			continue;
+
+		isl_int_add(bmap->ineq[last_pos][0],
+			    bmap->ineq[last_pos][0], bmap->ineq[last_neg][0]);
+		isl_int_add_ui(bmap->ineq[last_pos][0],
+			       bmap->ineq[last_pos][0], 1);
+		redundant = isl_int_ge(bmap->ineq[last_pos][0],
+				bmap->ineq[last_pos][1+off+i]);
+		isl_int_sub_ui(bmap->ineq[last_pos][0],
+			       bmap->ineq[last_pos][0], 1);
+		isl_int_sub(bmap->ineq[last_pos][0],
+			    bmap->ineq[last_pos][0], bmap->ineq[last_neg][0]);
+		if (!redundant)
+			continue;
+		if (last_pos > last_neg) {
+			isl_basic_map_drop_inequality(bmap, last_pos);
+			isl_basic_map_drop_inequality(bmap, last_neg);
+		} else {
+			isl_basic_map_drop_inequality(bmap, last_neg);
+			isl_basic_map_drop_inequality(bmap, last_pos);
+		}
+		bmap = isl_basic_map_drop_div(bmap, i);
+		return isl_basic_map_drop_redundant_divs(bmap);
+	}
+
+	return bmap;
+error:
+	isl_basic_map_free(bmap);
+	return NULL;
+}