Represent never returning as always_true && always_false

Expressions that never return are vacuously always both true and false.
Using this representation lets us take advantage of existing truth-based
optimizations, which gets us optimizations of command lines like

    bfs -name foo -quit -print

for free.

1 files changed, 5 insertions, 2 deletions

diff --git a/bfs.h b/bfs.h
index 16ce475..79a383a 100644
--- a/bfs.h
+++ b/bfs.h
@@ -206,8 +206,6 @@ struct expr {
 	bool always_true;
 	/** Whether this expression always evaluates to false. */
 	bool always_false;
-	/** Whether this expression never returns. */
-	bool never_returns;
 
 	/** Number of times this predicate was executed. */
 	size_t evaluations;
@@ -266,6 +264,11 @@ struct expr {
 };
 
 /**
+ * @return Whether expr is known to always quit.
+ */
+bool expr_never_returns(const struct expr *expr);
+
+/**
  * Parse the command line.
  */
 struct cmdline *parse_cmdline(int argc, char *argv[]);