disallow phi nodes in the start block

AFL found this bug.

1 files changed, 1 insertions, 1 deletions

diff --git a/parse.c b/parse.c
index ed88114..a06d5b9 100644
--- a/parse.c
+++ b/parse.c
@@ -578,7 +578,7 @@ parseline(PState ps)
 	op = next();
 DoOp:
 	if (op == Tphi) {
-		if (ps != PPhi)
+		if (ps != PPhi || curb == curf->start)
 			err("unexpected phi instruction");
 		op = -1;
 	}