soften heuristic of 316b57

Instead of systematically spilling any
temp live in an exit branch but not in
the part of the loop already processed,
only spill when it is already known to
have been spilled.

1 files changed, 15 insertions, 4 deletions

diff --git a/spill.c b/spill.c
index 2f7ebb2..04afaca 100644
--- a/spill.c
+++ b/spill.c
@@ -280,6 +280,19 @@ dopm(Blk *b, Ins *i, BSet *v)
 	return i;
 }
 
+static void
+merge(BSet *u, Blk *bu, BSet *v, Blk *bv)
+{
+	int t;
+
+	if (bu->loop <= bv->loop)
+		bsunion(u, v);
+	else
+		for (t=0; bsiter(v, &t); t++)
+			if (tmp[t].slot == -1)
+				bsset(u, t);
+}
+
 /* spill code insertion
  * requires spill costs, rpo, liveness
  *
@@ -364,12 +377,10 @@ spill(Fn *fn)
 			 * in the middle of loops */
 			bszero(v);
 			liveon(w, b, s1);
-			if (s1->loop >= b->loop)
-				bsunion(v, w);
+			merge(v, b, w, s1);
 			if (s2) {
 				liveon(u, b, s2);
-				if (s2->loop >= b->loop)
-					bsunion(v, u);
+				merge(v, b, u, s2);
 				bsinter(w, u);
 			}
 			limit2(v, 0, 0, w);