fix corner case in `dead_code` (#3579)

fixes #3578

2 files changed, 33 insertions, 4 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 26d17295..08728bb4 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6545,7 +6545,8 @@ merge(Compressor.prototype, {
             } else if (self.left instanceof AST_SymbolRef) {
                 if (self.left.is_immutable()) return strip_assignment();
                 var def = self.left.definition();
-                var local = def.scope.resolve() === compressor.find_parent(AST_Lambda);
+                var scope = def.scope.resolve();
+                var local = scope === compressor.find_parent(AST_Lambda);
                 var level = 0, node, parent = self;
                 do {
                     node = parent;
@@ -6553,12 +6554,13 @@ merge(Compressor.prototype, {
                     if (parent instanceof AST_Assign) {
                         if (!(parent.left instanceof AST_SymbolRef)) continue;
                         if (parent.left.definition() !== def) continue;
+                        if (in_try(level, parent)) break;
                         def.fixed = false;
                         return strip_assignment();
                     } else if (parent instanceof AST_Exit) {
                         if (!local) break;
                         if (in_try(level, parent)) break;
-                        if (is_reachable(def.scope, [ def ])) break;
+                        if (is_reachable(scope, [ def ])) break;
                         def.fixed = false;
                         return strip_assignment();
                     }
@@ -6604,9 +6606,9 @@ merge(Compressor.prototype, {
             self.right = make_node(AST_Null, right);
             var may_throw = node.may_throw(compressor);
             self.right = right;
-            var scope = self.left.definition().scope.resolve();
             var parent;
-            while ((parent = compressor.parent(level++)) !== scope) {
+            while (parent = compressor.parent(level++)) {
+                if (parent === scope) return false;
                 if (parent instanceof AST_Try) {
                     if (parent.bfinally) return true;
                     if (may_throw && parent.bcatch) return true;
diff --git a/test/compress/dead-code.js b/test/compress/dead-code.js
index abc7384d..d4832c73 100644
--- a/test/compress/dead-code.js
+++ b/test/compress/dead-code.js
@@ -1102,3 +1102,30 @@ catch_return_assign: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3578: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        var a = "FAIL", b, c;
+        try {
+            b = c.p = b = 0;
+        } catch (e) {
+            b += 42;
+            b && (a = "PASS");
+        }
+        console.log(a);
+    }
+    expect: {
+        var a = "FAIL", b, c;
+        try {
+            b = c.p = b = 0;
+        } catch (e) {
+            b += 42;
+            b && (a = "PASS");
+        }
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}