Fix invalid removal of left side in && and || compression

See #637. This does not produce the optimal result, but it does prevent the removal of non-side-effect-free code.

2 files changed, 34 insertions, 0 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 27285984..b77b5ff3 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2110,6 +2110,12 @@ merge(Compressor.prototype, {
             var rr = self.right.evaluate(compressor);
             if ((ll.length > 1 && !ll[1]) || (rr.length > 1 && !rr[1])) {
                 compressor.warn("Boolean && always false [{file}:{line},{col}]", self.start);
+                if (self.left.has_side_effects(compressor)) {
+                    return make_node(AST_Seq, self, {
+                        car: self.left,
+                        cdr: make_node(AST_False)
+                    }).optimize(compressor);
+                }
                 return make_node(AST_False, self);
             }
             if (ll.length > 1 && ll[1]) {
@@ -2124,6 +2130,12 @@ merge(Compressor.prototype, {
             var rr = self.right.evaluate(compressor);
             if ((ll.length > 1 && ll[1]) || (rr.length > 1 && rr[1])) {
                 compressor.warn("Boolean || always true [{file}:{line},{col}]", self.start);
+                if (self.left.has_side_effects(compressor)) {
+                    return make_node(AST_Seq, self, {
+                        car: self.left,
+                        cdr: make_node(AST_True)
+                    }).optimize(compressor);
+                }
                 return make_node(AST_True, self);
             }
             if (ll.length > 1 && !ll[1]) {
diff --git a/test/compress/issue-637.js b/test/compress/issue-637.js
new file mode 100644
index 00000000..45fd2481
--- /dev/null
+++ b/test/compress/issue-637.js
@@ -0,0 +1,22 @@
+wrongly_optimized: {
+    options = {
+        conditionals: true,
+        booleans: true,
+        evaluate: true
+    };
+    input: {
+        function func() {
+            foo();
+        }
+        if (func() || true) {
+            bar();
+        }
+    }
+    expect: {
+        function func() {
+            foo();
+        }
+        // TODO: optimize to `func(), bar()`
+        (func(), 0) || bar();
+    }
+}