improve compression of loop conditions (#2543)

test/compress/dead-code.js

@@ -129,8 +129,8 @@ dead_code_constant_boolean_should_warn_more: {
         function bar() {}
         // nothing for the while
         // as for the for, it should keep:
-        var x = 10, y;
         var moo;
+        var x = 10, y;
         bar();
     }
     expect_stdout: true
@@ -165,8 +165,8 @@ dead_code_constant_boolean_should_warn_more_strict: {
         var foo;
         // nothing for the while
         // as for the for, it should keep:
-        var x = 10, y;
         var moo;
+        var x = 10, y;
         bar();
     }
     expect_stdout: true

test/compress/issue-1656.js

@@ -39,7 +39,7 @@ f7: {
         "var b = 10;",
         "",
         "!function() {",
-        "    for (;b = 100, !1; ) ;",
+        "    b = 100;",
         "}(), console.log(100, b);",
     ]
     expect_stdout: true

test/compress/issue-1833.js

@@ -134,5 +134,5 @@ label_while: {
             L: while (0) continue L;
         }
     }
-    expect_exact: "function f(){L:;}"
+    expect_exact: "function f(){L:0}"
 }

test/compress/loops.js

@@ -148,9 +148,11 @@ parse_do_while_without_semicolon: {
 
 evaluate: {
     options = {
-        loops: true,
         dead_code: true,
         evaluate: true,
+        loops: true,
+        passes: 2,
+        side_effects: true,
     };
     input: {
         while (true) {

test/compress/reduce_vars.js

@@ -1209,6 +1209,7 @@ toplevel_on_loops_2: {
         loops: true,
         reduce_funcs: true,
         reduce_vars: true,
+        side_effects: true,
         toplevel:true,
         unused: true,
     }