fix corner case in `switches` (#5013)

fixes #5012

3 files changed, 55 insertions, 31 deletions

diff --git a/lib/compress.js b/lib/compress.js
index ed3b5a39..22434f62 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -8422,7 +8422,7 @@ merge(Compressor.prototype, {
         var default_branch;
         var exact_match;
         var side_effects = [];
-        for (var i = 0, len = self.body.length; i < len && !exact_match; i++) {
+        for (var i = 0, len = self.body.length; i < len; i++) {
             branch = self.body[i];
             if (branch instanceof AST_Default) {
                 var prev = body[body.length - 1];
@@ -8445,16 +8445,21 @@ merge(Compressor.prototype, {
                     continue;
                 }
                 if (!(equals instanceof AST_Node)) {
-                    exact_match = branch;
                     if (default_branch) {
                         var default_index = body.indexOf(default_branch);
                         body.splice(default_index, 1);
                         eliminate_branch(default_branch, body[default_index - 1]);
                         default_branch = null;
                     }
+                    if (exp.has_side_effects(compressor)) {
+                        exact_match = branch;
+                    } else {
+                        default_branch = branch = make_node(AST_Default, branch, branch);
+                    }
+                    while (++i < len) eliminate_branch(self.body[i], branch);
                 }
             }
-            if (exact_match || i == len - 1 || aborts(branch)) {
+            if (i + 1 >= len || aborts(branch)) {
                 var prev = body[body.length - 1];
                 var statements = branch.body;
                 if (aborts(prev)) switch (prev.body.length - statements.length) {
@@ -8479,7 +8484,6 @@ merge(Compressor.prototype, {
             }
             body.push(branch);
         }
-        while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
         if (side_effects.length && !exact_match) {
             body.push(make_node(AST_Case, self, { expression: make_sequence(self, side_effects), body: [] }));
         }
@@ -8506,23 +8510,17 @@ merge(Compressor.prototype, {
             }));
             return make_node(AST_BlockStatement, self, { body: decl }).optimize(compressor);
         }
-        if (branch === default_branch || branch === exact_match && !branch.expression.has_side_effects(compressor)) {
-            while (branch = body[body.length - 2]) {
-                if (branch instanceof AST_Default) break;
-                if (!has_declarations_only(branch)) break;
-                var exp = branch.expression;
-                if (exp.has_side_effects(compressor)) {
-                    var prev = body[body.length - 3];
-                    if (prev && !aborts(prev)) break;
-                    if (exact_match) {
-                        exact_match.expression = make_sequence(self, [ exp, exact_match.expression ]);
-                    } else {
-                        default_branch.body.unshift(make_node(AST_SimpleStatement, self, { body: exp }));
-                    }
-                }
-                eliminate_branch(branch);
-                body.splice(-2, 1);
+        if (branch === default_branch) while (branch = body[body.length - 2]) {
+            if (branch instanceof AST_Default) break;
+            if (!has_declarations_only(branch)) break;
+            var exp = branch.expression;
+            if (exp.has_side_effects(compressor)) {
+                var prev = body[body.length - 3];
+                if (prev && !aborts(prev)) break;
+                default_branch.body.unshift(make_node(AST_SimpleStatement, self, { body: exp }));
             }
+            eliminate_branch(branch);
+            body.splice(-2, 1);
         }
         body[0].body = decl.concat(body[0].body);
         self.body = body;
diff --git a/test/compress/merge_vars.js b/test/compress/merge_vars.js
index dc526c5f..e29298ed 100644
--- a/test/compress/merge_vars.js
+++ b/test/compress/merge_vars.js
@@ -3075,7 +3075,7 @@ issue_4237_2: {
         console.log(function(a) {
             do {
                 switch (0) {
-                  case 0:
+                  default:
                     var b = a++;
                     if (b)
                         return "FAIL";
diff --git a/test/compress/switches.js b/test/compress/switches.js
index af81b54c..3c43612e 100644
--- a/test/compress/switches.js
+++ b/test/compress/switches.js
@@ -113,7 +113,7 @@ constant_switch_5: {
         // the break inside the if ruins our job
         // we can still get rid of irrelevant cases.
         switch (1) {
-          case 1:
+          default:
             x();
             if (foo) break;
             y();
@@ -501,7 +501,8 @@ drop_case_5: {
     }
     expect: {
         switch (42) {
-          case (void console.log("PASS 1"), 42):
+          default:
+            void console.log("PASS 1");
             console.log("PASS 2");
         }
     }
@@ -554,7 +555,8 @@ drop_case_7: {
     }
     expect: {
         switch (2) {
-          case (console.log("PASS 1"), 1, 2):
+          default:
+            console.log("PASS 1"), 1;
             console.log("PASS 2");
         }
     }
@@ -920,7 +922,7 @@ issue_1680_1: {
           case f(0):
           case f(1):
             f(2);
-          case 2:
+          default:
             f(5);
         }
     }
@@ -1183,7 +1185,6 @@ issue_2535: {
     }
     expect: {
         w(), 42;
-        42;
         y();
         z();
     }
@@ -1209,7 +1210,6 @@ issue_1750: {
     expect: {
         var a = 0, b = 1;
         true;
-        a, true;
         b = 2;
         console.log(a, b);
     }
@@ -1463,7 +1463,7 @@ issue_5008_1: {
     expect: {
         console.log(function f() {
             switch (f) {
-              case f:
+              default:
                 return "PASS";
             }
         }());
@@ -1492,7 +1492,7 @@ issue_5008_2: {
     expect: {
         console.log(function(a) {
             switch (a) {
-              case a:
+              default:
                 return "PASS";
             }
         }([]));
@@ -1521,7 +1521,7 @@ issue_5008_3: {
     expect: {
         console.log(function(a) {
             switch (a) {
-              case a:
+              default:
                 return "PASS";
             }
         }({}));
@@ -1549,7 +1549,7 @@ issue_5008_4: {
     expect: {
         console.log(function(a) {
             switch (a) {
-              case a:
+              default:
                 return "PASS";
             }
         }(/foo/));
@@ -1582,3 +1582,29 @@ issue_5010: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5012: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        switches: true,
+    }
+    input: {
+        switch (void 0) {
+          case console.log("PASS"):
+            break;
+          case void 0:
+          case 42:
+            console.log("FAIL");
+        }
+    }
+    expect: {
+        switch (void 0) {
+          case console.log("PASS"):
+            break;
+          default:
+            console.log("FAIL");
+        }
+    }
+    expect_stdout: "PASS"
+}