enhance `unused` (#3794)

6 files changed, 54 insertions, 30 deletions

diff --git a/lib/compress.js b/lib/compress.js
index d6f6a710..3aa9f0bc 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4134,6 +4134,7 @@ merge(Compressor.prototype, {
                 // side effects, we can cascade the init. code
                 // into the next one, or next statement.
                 var side_effects = [];
+                var duplicated = 0;
                 node.definitions.forEach(function(def) {
                     if (def.value) def.value = def.value.transform(tt);
                     var sym = def.name.definition();
@@ -4142,24 +4143,17 @@ merge(Compressor.prototype, {
                             def.value = def.value.drop_side_effect_free(compressor);
                         }
                         var var_defs = var_defs_by_id.get(sym.id);
-                        if (var_defs.length > 1 && (!def.value || sym.orig.indexOf(def.name) > sym.eliminated)) {
-                            AST_Node.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
-                            if (def.value) {
-                                var ref = make_node(AST_SymbolRef, def.name, def.name);
-                                sym.references.push(ref);
-                                var assign = make_node(AST_Assign, def, {
-                                    operator: "=",
-                                    left: ref,
-                                    right: def.value
-                                });
-                                if (fixed_ids[sym.id] === def) {
-                                    fixed_ids[sym.id] = assign;
-                                }
-                                side_effects.push(assign.transform(tt));
+                        if (var_defs.length > 1) {
+                            if (!def.value) {
+                                AST_Node.warn("Dropping duplicated declaration of variable {name} [{file}:{line},{col}]", template(def.name));
+                                remove(var_defs, def);
+                                sym.eliminated++;
+                                return;
+                            }
+                            if (sym.orig.indexOf(def.name) > sym.eliminated) {
+                                remove(var_defs, def);
+                                duplicated++;
                             }
-                            remove(var_defs, def);
-                            sym.eliminated++;
-                            return;
                         }
                         if (!def.value) {
                             head.push(def);
@@ -4220,7 +4214,22 @@ merge(Compressor.prototype, {
                         return !def || fn.name && def === fn.name.definition();
                     }
                 });
-                if (head.length > 0 || tail.length > 0) {
+                if (head.length == 0 && tail.length == duplicated) {
+                    [].unshift.apply(side_effects, tail.map(function(def) {
+                        AST_Node.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
+                        var sym = def.name.definition();
+                        var ref = make_node(AST_SymbolRef, def.name, def.name);
+                        sym.references.push(ref);
+                        var assign = make_node(AST_Assign, def, {
+                            operator: "=",
+                            left: ref,
+                            right: def.value
+                        });
+                        if (fixed_ids[sym.id] === def) fixed_ids[sym.id] = assign;
+                        sym.eliminated++;
+                        return assign.transform(tt);
+                    }));
+                } else if (head.length > 0 || tail.length > 0) {
                     node.definitions = head.concat(tail);
                     body.push(node);
                 }
diff --git a/test/compress/asm.js b/test/compress/asm.js
index 0ea60874..54cf90f4 100644
--- a/test/compress/asm.js
+++ b/test/compress/asm.js
@@ -91,8 +91,7 @@ asm_mixed: {
         function no_asm_GeometricMean(stdlib, foreign, buffer) {
             function logSum(start, end) {
                 start |= 0, end |= 0;
-                var sum = 0, p = 0, q = 0;
-                for (p = start << 3, q = end << 3; (0 | p) < (0 | q); p = p + 8 | 0) sum += +log(values[p >> 3]);
+                for (var sum = 0, p = 0, q = 0, p = start << 3, q = end << 3; (0 | p) < (0 | q); p = p + 8 | 0) sum += +log(values[p >> 3]);
                 return +sum;
             }
             function geometricMean(start, end) {
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 1c3af6fa..17d9c981 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -2570,8 +2570,7 @@ chained_3: {
     }
     expect: {
         console.log(function(a, b) {
-            var c = 1;
-            c = b;
+            var c = 1, c = b;
             b++;
             return c;
         }(0, 2));
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
index 99ab7b40..0f4c6dc6 100644
--- a/test/compress/drop-unused.js
+++ b/test/compress/drop-unused.js
@@ -2444,3 +2444,23 @@ issue_3746: {
     }
     expect_stdout: "PASS"
 }
+
+drop_duplicated_side_effects: {
+    options = {
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = 0;
+        for (var i = 1; i--;)
+            var a = 0, b = ++a;
+        console.log(a);
+    }
+    expect: {
+        var a = 0;
+        for (var i = 1; i--;)
+            a = 0, ++a;
+        console.log(a);
+    }
+    expect_stdout: "1"
+}
diff --git a/test/compress/keep_fargs.js b/test/compress/keep_fargs.js
index 85fcb0bf..c2a4ceef 100644
--- a/test/compress/keep_fargs.js
+++ b/test/compress/keep_fargs.js
@@ -1226,8 +1226,7 @@ chained_3: {
     }
     expect: {
         console.log(function(b) {
-            var c = 1;
-            c = b;
+            var c = 1, c = b;
             b++;
             return c;
         }(2));
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 4e11de48..6be1171f 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -5434,8 +5434,7 @@ lvalues_def_1: {
     }
     expect: {
         var b = 1;
-        var a = b++;
-        b = NaN;
+        var a = b++, b = NaN;
         console.log(a, b);
     }
     expect_stdout: "1 NaN"
@@ -5454,8 +5453,7 @@ lvalues_def_2: {
     }
     expect: {
         var b = 1;
-        var a = b += 1;
-        b = NaN;
+        var a = b += 1, b = NaN;
         console.log(a, b);
     }
     expect_stdout: "2 NaN"
@@ -6867,9 +6865,9 @@ issue_3666: {
         } finally {
             for (;!a;)
                 a++;
-            var b = a = "PASS";
+            a = "PASS";
         }
-        console.log(a, b);
+        console.log(a, "PASS");
     }
     expect_stdout: "PASS PASS"
 }