From 4216dbac10887476feef287854e9e4037f2d1a59 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 21 Mar 2019 21:24:24 -0400
Subject: opt: Optimize redundant comma expressions

---
 opt.c                                |  8 +++++---
 tests.sh                             | 16 ++++++++++++++--
 tests/test_comma_redundant_false.out |  1 +
 tests/test_comma_redundant_true.out  |  1 +
 4 files changed, 21 insertions(+), 5 deletions(-)
 create mode 100644 tests/test_comma_redundant_false.out
 create mode 100644 tests/test_comma_redundant_true.out

diff --git a/opt.c b/opt.c
index fd2dc3c..1ece9be 100644
--- a/opt.c
+++ b/opt.c
@@ -595,9 +595,11 @@ static struct expr *optimize_comma_expr(const struct opt_state *state, struct ex
 		if (expr_never_returns(lhs)) {
 			debug_opt(state, "-O1: reachability: %e <==> %e\n", expr, lhs);
 			return extract_child_expr(expr, &expr->lhs);
-		}
-
-		if (optlevel >= 2 && lhs->pure) {
+		} else if ((lhs->always_true && rhs == &expr_true)
+			   || (lhs->always_false && rhs == &expr_false)) {
+			debug_opt(state, "-O1: redundancy elimination: %e <==> %e\n", expr, lhs);
+			return extract_child_expr(expr, &expr->lhs);
+		} else if (optlevel >= 2 && lhs->pure) {
 			debug_opt(state, "-O2: purity: %e <==> %e\n", expr, rhs);
 			return extract_child_expr(expr, &expr->rhs);
 		}
diff --git a/tests.sh b/tests.sh
index 4006534..bd3f399 100755
--- a/tests.sh
+++ b/tests.sh
@@ -610,6 +610,8 @@ gnu_tests=(
     test_not_reachability
     test_comma_reachability
     test_and_false_or_true
+    test_comma_redundant_true
+    test_comma_redundant_false
 )
 
 bfs_tests=(
@@ -2005,11 +2007,21 @@ function test_de_morgan_or() {
 }
 
 function test_and_false_or_true() {
-    # Test (-a lhs(always_true) false) <==> (! lhs),
-    # (-a lhs(always_false) true) <==> (! lhs)
+    # Test (-a lhs(always_true) -false) <==> (! lhs),
+    # (-a lhs(always_false) -true) <==> (! lhs)
     bfs_diff basic -prune -false -o -true
 }
 
+function test_comma_redundant_true() {
+    # Test (, lhs(always_true) -true) <==> lhs,
+    bfs_diff basic -prune , -true
+}
+
+function test_comma_redundant_false() {
+    # Test (, lhs(always_false) -false) <==> lhs,
+    bfs_diff basic -print -not -prune , -false
+}
+
 function test_data_flow_depth() {
     bfs_diff basic -depth +1 -depth -4
 }
diff --git a/tests/test_comma_redundant_false.out b/tests/test_comma_redundant_false.out
new file mode 100644
index 0000000..15a13db
--- /dev/null
+++ b/tests/test_comma_redundant_false.out
@@ -0,0 +1 @@
+basic
diff --git a/tests/test_comma_redundant_true.out b/tests/test_comma_redundant_true.out
new file mode 100644
index 0000000..15a13db
--- /dev/null
+++ b/tests/test_comma_redundant_true.out
@@ -0,0 +1 @@
+basic
-- 
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