Fix a couple terrible optimizer bugs

Just because an expression is always true or false, doesn't mean we can
execute it more often than it otherwise would be, unless it's also pure.
But that's equivalent to being identically -true/-false, so just check
that.

4 files changed, 14 insertions, 2 deletions

diff --git a/parse.c b/parse.c
index d4e945c..61c17a5 100644
--- a/parse.c
+++ b/parse.c
@@ -2568,7 +2568,7 @@ static struct expr *new_and_expr(const struct parser_state *state, struct expr *
 			debug_opt(state, "-O1: short-circuit: (%s %e %e) <==> %e\n", argv[0], lhs, rhs, lhs);
 			free_expr(rhs);
 			return lhs;
-		} else if (optlevel >= 2 && rhs->always_false && lhs->pure) {
+		} else if (optlevel >= 2 && lhs->pure && rhs == &expr_false) {
 			debug_opt(state, "-O2: purity: (%s %e %e) <==> %e\n", argv[0], lhs, rhs, rhs);
 			free_expr(lhs);
 			return rhs;
@@ -2664,7 +2664,7 @@ static struct expr *new_or_expr(const struct parser_state *state, struct expr *l
 		} else if (rhs == &expr_false) {
 			debug_opt(state, "-O1: disjunctive syllogism: (%s %e %e) <==> %e\n", argv[0], lhs, rhs, lhs);
 			return lhs;
-		} else if (optlevel >= 2 && rhs->always_true && lhs->pure) {
+		} else if (optlevel >= 2 && lhs->pure && rhs == &expr_true) {
 			debug_opt(state, "-O2: purity: (%s %e %e) <==> %e\n", argv[0], lhs, rhs, rhs);
 			free_expr(lhs);
 			return rhs;
diff --git a/tests.sh b/tests.sh
index d7e9287..87724d9 100755
--- a/tests.sh
+++ b/tests.sh
@@ -346,6 +346,8 @@ gnu_tests=(
     test_or
     test_comma
     test_precedence
+    test_and_purity
+    test_or_purity
 )
 
 bfs_tests=(
@@ -1232,6 +1234,16 @@ function test_printx() {
     bfs_diff weirdnames -printx
 }
 
+function test_and_purity() {
+    # Regression test: (-a lhs(pure) rhs(always_false)) <==> rhs is only valid if rhs is pure
+    bfs_diff basic -name nonexistent \( -print , -false \)
+}
+
+function test_or_purity() {
+    # Regression test: (-o lhs(pure) rhs(always_true)) <==> rhs is only valid if rhs is pure
+    bfs_diff basic -name '*' -o -print
+}
+
 passed=0
 failed=0
 
diff --git a/tests/test_and_purity.out b/tests/test_and_purity.out
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/test_and_purity.out
diff --git a/tests/test_or_purity.out b/tests/test_or_purity.out
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/test_or_purity.out