fix corner cases in switch and undefined (#1762)

- fix side effects in switch condition for singular blocks
- fix `undefined` confusion with local variable
- gate `OPT(AST_Switch)` with `switches`

fixes #1758
fixes #1759

test/compress/switch.js

@@ -1,5 +1,10 @@
 constant_switch_1: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (1+1) {
           case 1: foo(); break;
@@ -13,7 +18,12 @@ constant_switch_1: {
 }
 
 constant_switch_2: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (1) {
           case 1: foo();
@@ -28,7 +38,12 @@ constant_switch_2: {
 }
 
 constant_switch_3: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (10) {
           case 1: foo();
@@ -44,7 +59,12 @@ constant_switch_3: {
 }
 
 constant_switch_4: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (2) {
           case 1:
@@ -65,7 +85,12 @@ constant_switch_4: {
 }
 
 constant_switch_5: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (1) {
           case 1:
@@ -94,7 +119,12 @@ constant_switch_5: {
 }
 
 constant_switch_6: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: {
             foo();
@@ -123,7 +153,12 @@ constant_switch_6: {
 }
 
 constant_switch_7: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: {
             foo();
@@ -161,7 +196,12 @@ constant_switch_7: {
 }
 
 constant_switch_8: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: switch (1) {
           case 1:
@@ -185,7 +225,12 @@ constant_switch_8: {
 }
 
 constant_switch_9: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: switch (1) {
           case 1:
@@ -210,7 +255,10 @@ constant_switch_9: {
 }
 
 drop_default_1: {
-    options = { dead_code: true };
+    options = {
+        dead_code: true,
+        switches: true,
+    }
     input: {
         switch (foo) {
           case 'bar': baz();
@@ -225,7 +273,10 @@ drop_default_1: {
 }
 
 drop_default_2: {
-    options = { dead_code: true };
+    options = {
+        dead_code: true,
+        switches: true,
+    }
     input: {
         switch (foo) {
           case 'bar': baz(); break;
@@ -241,7 +292,10 @@ drop_default_2: {
 }
 
 keep_default: {
-    options = { dead_code: true };
+    options = {
+        dead_code: true,
+        switches: true,
+    }
     input: {
         switch (foo) {
           case 'bar': baz();
@@ -263,6 +317,8 @@ issue_1663: {
     options = {
         dead_code: true,
         evaluate: true,
+        side_effects: true,
+        switches: true,
     }
     input: {
         var a = 100, b = 10;
@@ -294,6 +350,7 @@ issue_1663: {
 drop_case: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -312,6 +369,7 @@ drop_case: {
 keep_case: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -332,6 +390,7 @@ issue_376: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         switch (true) {
@@ -354,6 +413,7 @@ issue_376: {
 issue_441_1: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -381,6 +441,7 @@ issue_441_1: {
 issue_441_2: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -414,6 +475,8 @@ issue_1674: {
     options = {
         dead_code: true,
         evaluate: true,
+        side_effects: true,
+        switches: true,
     }
     input: {
         switch (0) {
@@ -435,6 +498,7 @@ issue_1679: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         var a = 100, b = 10;
@@ -482,6 +546,7 @@ issue_1680_1: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         function f(x) {
@@ -522,6 +587,7 @@ issue_1680_1: {
 issue_1680_2: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         var a = 100, b = 10;
@@ -557,6 +623,7 @@ issue_1680_2: {
 issue_1690_1: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (console.log("PASS")) {}
@@ -570,6 +637,7 @@ issue_1690_1: {
 issue_1690_2: {
     options = {
         dead_code: false,
+        switches: true,
     }
     input: {
         switch (console.log("PASS")) {}
@@ -585,6 +653,7 @@ if_switch_typeof: {
         conditionals: true,
         dead_code: true,
         side_effects: true,
+        switches: true,
     }
     input: {
         if (a) switch(typeof b) {}
@@ -597,6 +666,7 @@ if_switch_typeof: {
 issue_1698: {
     options = {
         side_effects: true,
+        switches: true,
     }
     input: {
         var a = 1;
@@ -618,6 +688,7 @@ issue_1698: {
 issue_1705_1: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         var a = 0;
@@ -646,6 +717,7 @@ issue_1705_2: {
         reduce_vars: true,
         sequences: true,
         side_effects: true,
+        switches: true,
         toplevel: true,
         unused: true,
     }
@@ -666,6 +738,7 @@ issue_1705_2: {
 issue_1705_3: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (a) {
@@ -721,3 +794,25 @@ beautify: {
         "}",
     ]
 }
+
+issue_1758: {
+    options = {
+        dead_code: true,
+        switches: true,
+    }
+    input: {
+        var a = 1, b = 2;
+        switch (a--) {
+          default:
+            b++;
+        }
+        console.log(a, b);
+    }
+    expect: {
+        var a = 1, b = 2;
+        a--;
+        b++;
+        console.log(a, b);
+    }
+    expect_stdout: "0 3"
+}