From 462589f69859354a9c623cad9015821e769beecb Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Fri, 21 Jul 2017 19:09:10 -0400
Subject: 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.
---
 parse.c                   |  4 ++--
 tests.sh                  | 12 ++++++++++++
 tests/test_and_purity.out |  0
 tests/test_or_purity.out  |  0
 4 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 tests/test_and_purity.out
 create mode 100644 tests/test_or_purity.out

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
diff --git a/tests/test_or_purity.out b/tests/test_or_purity.out
new file mode 100644
index 0000000..e69de29
-- 
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