fix corner case in switches (#5009)

fixes #5008

lib/compress.js

@@ -8108,10 +8108,6 @@ merge(Compressor.prototype, {
                 cond = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
             } else if (cond) {
                 self.condition = null;
-            } else if (!compressor.option("dead_code")) {
-                var orig = self.condition;
-                self.condition = make_node_from_constant(cond, self.condition);
-                self.condition = best_of_expression(self.condition.transform(compressor), orig);
             }
             if (!cond) {
                 if (compressor.option("dead_code")) {
@@ -8226,13 +8222,8 @@ merge(Compressor.prototype, {
         // one of the blocks.  note, statically determined implies
         // “has no side effects”; also it doesn't work for cases like
         // `x && true`, though it probably should.
-        var cond = self.condition.evaluate(compressor);
-        if (!compressor.option("dead_code") && !(cond instanceof AST_Node)) {
-            var orig = self.condition;
-            self.condition = make_node_from_constant(cond, orig);
-            self.condition = best_of_expression(self.condition.transform(compressor), orig);
-        }
         if (compressor.option("dead_code")) {
+            var cond = self.condition.evaluate(compressor);
             if (cond instanceof AST_Node) {
                 cond = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
             }
@@ -8424,16 +8415,7 @@ merge(Compressor.prototype, {
 
     OPT(AST_Switch, function(self, compressor) {
         if (!compressor.option("switches")) return self;
-        var value = self.expression.evaluate(compressor);
-        if (!(value instanceof AST_Node)) {
-            var orig = self.expression;
-            self.expression = make_node_from_constant(value, orig);
-            self.expression = best_of_expression(self.expression.transform(compressor), orig);
-        }
         if (!compressor.option("dead_code")) return self;
-        if (value instanceof AST_Node) {
-            value = self.expression.evaluate(compressor, true);
-        }
         var body = [];
         var branch;
         var decl = [];
@@ -8450,10 +8432,19 @@ merge(Compressor.prototype, {
                 } else {
                     default_branch = branch;
                 }
-            } else if (!(value instanceof AST_Node)) {
+            } else {
                 var exp = branch.expression;
-                var val = exp.evaluate(compressor, true);
+                var equals = make_node(AST_Binary, self, {
-                if (val === value) {
+                    operator: "===",
+                    left: self.expression,
+                    right: exp,
+                }).evaluate(compressor, true);
+                if (!equals) {
+                    if (exp.has_side_effects(compressor)) side_effects.push(exp);
+                    eliminate_branch(branch, body[body.length - 1]);
+                    continue;
+                }
+                if (!(equals instanceof AST_Node)) {
                     exact_match = branch;
                     if (default_branch) {
                         var default_index = body.indexOf(default_branch);
@@ -8461,10 +8452,6 @@ merge(Compressor.prototype, {
                         eliminate_branch(default_branch, body[default_index - 1]);
                         default_branch = null;
                     }
-                } else if (!(val instanceof AST_Node)) {
-                    if (exp.has_side_effects(compressor)) side_effects.push(exp);
-                    eliminate_branch(branch, body[body.length - 1]);
-                    continue;
                 }
             }
             if (exact_match || i == len - 1 || aborts(branch)) {

test/compress/switches.js

@@ -1441,3 +1441,118 @@ issue_4059: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5008_1: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        reduce_vars: true,
+        switches: true,
+        unsafe: true,
+    }
+    input: {
+        console.log(function f() {
+            switch (f) {
+              case f:
+                return "PASS";
+              default:
+                return "FAIL";
+            }
+        }());
+    }
+    expect: {
+        console.log(function f() {
+            switch (f) {
+              case f:
+                return "PASS";
+            }
+        }());
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5008_2: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        reduce_vars: true,
+        switches: true,
+        unsafe: true,
+    }
+    input: {
+        console.log(function(a) {
+            switch (a) {
+              case a:
+                return "PASS";
+              default:
+                return "FAIL";
+            }
+        }([]));
+    }
+    expect: {
+        console.log(function(a) {
+            switch (a) {
+              case a:
+                return "PASS";
+            }
+        }([]));
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5008_3: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        reduce_vars: true,
+        switches: true,
+        unsafe: true,
+    }
+    input: {
+        console.log(function(a) {
+            switch (a) {
+              case a:
+                return "PASS";
+              default:
+                return "FAIL";
+            }
+        }({}));
+    }
+    expect: {
+        console.log(function(a) {
+            switch (a) {
+              case a:
+                return "PASS";
+            }
+        }({}));
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5008_4: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        reduce_vars: true,
+        switches: true,
+    }
+    input: {
+        console.log(function(a) {
+            switch (a) {
+              case a:
+                return "PASS";
+              default:
+                return "FAIL";
+            }
+        }(/foo/));
+    }
+    expect: {
+        console.log(function(a) {
+            switch (a) {
+              case a:
+                return "PASS";
+            }
+        }(/foo/));
+    }
+    expect_stdout: "PASS"
+}