add predecessor computation

lisc/ssa.c

@@ -0,0 +1,39 @@
+#include "lisc.h"
+
+static void
+addpred(Blk *bp, Blk *bc)
+{
+	int i;
+
+	if (!bc->preds) {
+		bc->preds = alloc(bc->npreds * sizeof(Blk*));
+		for (i=0; i<bc->npreds; i++)
+			bc->preds[i] = 0;
+	}
+	for (i=0; bc->preds[i]; i++)
+		;
+	bc->preds[i] = bp;
+}
+
+void
+fillpreds(Fn *f)
+{
+	Blk *b;
+
+	for (b=f->start; b; b=b->link) {
+		b->npreds = 0;
+		free(b->preds);
+	}
+	for (b=f->start; b; b=b->link) {
+		if (b->s1)
+			b->s1->npreds++;
+		if (b->s2)
+			b->s2->npreds++;
+	}
+	for (b=f->start; b; b=b->link) {
+		if (b->s1)
+			addpred(b, b->s1);
+		if (b->s2)
+			addpred(b, b->s2);
+	}
+}