fallthrough should not execute case expression (#1683)

- de-duplicate trailing cases only, avoid all potential side-effects
- enable switch statement fuzzing

fixes #1680

1 files changed, 7 insertions, 17 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 70bbb7fc..8467f96c 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2515,7 +2515,7 @@ merge(Compressor.prototype, {
             self.expression = best_of_expression(expression, self.expression);
         }
         if (compressor.option("dead_code")) {
-            var blocks = Object.create(null);
+            var prev_block;
             var decl = [];
             var body = [];
             var default_branch;
@@ -2542,31 +2542,21 @@ merge(Compressor.prototype, {
                         continue;
                     }
                 }
+                var case_side_effects = branch instanceof AST_Case && branch.expression.has_side_effects(compressor);
                 if (aborts(branch)) {
-                    var key = make_node(AST_BlockStatement, branch, branch).print_to_string();
-                    var block;
-                    if (!fallthrough && (block = blocks[key])) {
-                        block.body = [];
-                        body.splice(body.indexOf(block) + 1, 0, branch);
-                    } else {
-                        body.push(branch);
-                    }
+                    var block = make_node(AST_BlockStatement, branch, branch).print_to_string();
+                    if (!fallthrough && prev_block === block) body[body.length - 1].body = [];
+                    body.push(branch);
+                    prev_block = block;
                     fallthrough = false;
                 } else {
                     body.push(branch);
+                    prev_block = null;
                     fallthrough = true;
                 }
-                if (branch instanceof AST_Case && branch.expression.has_side_effects(compressor))
-                    blocks = Object.create(null);
-                if (!fallthrough) blocks[key] = branch;
             }
             for (; i < len && fallthrough; i++) {
                 branch = self.body[i];
-                if (branch instanceof AST_Case) {
-                    exact_match.body.push(make_node(AST_SimpleStatement, branch.expression, {
-                        body: branch.expression
-                    }));
-                }
                 exact_match.body = exact_match.body.concat(branch.body);
                 fallthrough = !aborts(exact_match);
             }