enhance reduce_vars & unused (#4890)

lib/compress.js

@@ -610,6 +610,11 @@ merge(Compressor.prototype, {
 
         function is_immutable(value) {
             if (!value) return false;
+            if (value instanceof AST_Assign) {
+                var op = value.operator;
+                return op == "=" ? is_immutable(value.right) : !lazy_op[op.slice(0, -1)];
+            }
+            if (value instanceof AST_Sequence) return is_immutable(value.tail_node());
             return value.is_constant() || is_lambda(value) || value instanceof AST_ObjectIdentity;
         }
 
@@ -901,6 +906,7 @@ merge(Compressor.prototype, {
 
             function walk_assign() {
                 right.walk(tw);
+                var modified = is_modified(compressor, tw, node, right, 0, is_immutable(right), recursive_ref(tw, d));
                 scan_declaration(tw, compressor, left, function() {
                     return node.right;
                 }, function(sym, fixed, walk) {
@@ -911,10 +917,7 @@ merge(Compressor.prototype, {
                     }
                     var d = sym.definition();
                     d.assignments++;
-                    if (fixed
+                    if (fixed && !modified && !sym.in_arg && safe_to_assign(tw, d)) {
-                        && !is_modified(compressor, tw, node, right, 0, is_immutable(right), recursive_ref(tw, d))
-                        && !sym.in_arg
-                        && safe_to_assign(tw, d)) {
                         push_ref(d, sym);
                         mark(tw, d);
                         if (d.single_use && left instanceof AST_Destructured) d.single_use = false;
@@ -6299,18 +6302,13 @@ merge(Compressor.prototype, {
                     var drop_sym = is_var ? can_drop_symbol(def.name) : is_safe_lexical(sym);
                     if (!drop_sym || !drop_vars || sym.id in in_use_ids) {
                         if (value && indexOf_assign(sym, def) < 0) {
-                            var write_only = value.write_only;
                             value = value.drop_side_effect_free(compressor);
-                            if (def.value !== value) {
                             if (value) {
                                 AST_Node.warn("Side effects in last use of variable {name} [{file}:{line},{col}]", template(def.name));
                                 side_effects.push(value);
                             }
                             value = null;
                             trim_defns.push(def);
-                            } else if (value.write_only !== write_only) {
-                                value.write_only = write_only;
-                            }
                         }
                         var old_def;
                         if (!value && !(node instanceof AST_Let)) {

test/compress/functions.js

@@ -6013,7 +6013,7 @@ issue_4823: {
         console.log(typeof function() {
             {
                 function f() {}
-                arguments = f();
+                f();
                 var arguments = function() {};
             }
             return f && arguments;
@@ -6040,3 +6040,171 @@ drop_unused_self_reference: {
     }
     expect_stdout: "PASS"
 }
+
+reduce_cross_reference_1: {
+    options = {
+        passes: 3,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function(a, b) {
+            a = b = function() {};
+            a.p = a;
+            b = a = function() {};
+            b.q = b;
+        })();
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_1_toplevel: {
+    options = {
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = b = function() {};
+        a.p = a;
+        var b = a = function() {};
+        b.q = b;
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_2: {
+    options = {
+        collapse_vars: true,
+        passes: 3,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function(a, b) {
+            a = b = function() {};
+            b.p = a;
+            b = a = function() {};
+            a.q = b;
+        })();
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_2_toplevel: {
+    options = {
+        collapse_vars: true,
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = b = function() {};
+        b.p = a;
+        var b = a = function() {};
+        a.q = b;
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_3: {
+    options = {
+        collapse_vars: true,
+        passes: 3,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function(a, b) {
+            a = b = function() {};
+            a.p = b;
+            b = a = function() {};
+            b.q = a;
+        })();
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_3_toplevel: {
+    options = {
+        collapse_vars: true,
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = b = function() {};
+        a.p = b;
+        var b = a = function() {};
+        b.q = a;
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_4: {
+    options = {
+        passes: 3,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function(a, b) {
+            a = b = function() {};
+            b.p = b;
+            b = a = function() {};
+            a.q = a;
+        })();
+    }
+    expect: {}
+    expect_stdout: true
+}
+
+reduce_cross_reference_4_toplevel: {
+    options = {
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = b = function() {};
+        b.p = b;
+        var b = a = function() {};
+        a.q = a;
+    }
+    expect: {}
+    expect_stdout: true
+}

test/compress/ie8.js

@@ -2653,7 +2653,9 @@ issue_4019: {
             try {
                 console.log("FAIL");
             } catch (o) {}
-        }, o = (console.log(o.length), ++o);
+        };
+        console.log(o.length),
+        ++o;
     }
     expect_stdout: "0"
 }