enhance `join_vars` (#4643)

1 files changed, 38 insertions, 7 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 3d857190..1eed09ba 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3049,13 +3049,13 @@ merge(Compressor.prototype, {
             statements.length = n;
         }
 
+        function extract_exprs(body) {
+            if (body instanceof AST_Assign) return [ body ];
+            if (body instanceof AST_Sequence) return body.expressions.slice();
+        }
+
         function join_assigns(defn, body, keep) {
-            var exprs;
-            if (body instanceof AST_Assign) {
-                exprs = [ body ];
-            } else if (body instanceof AST_Sequence) {
-                exprs = body.expressions.slice();
-            }
+            var exprs = extract_exprs(body);
             if (!exprs) return;
             var trimmed = false;
             for (var i = exprs.length - 1; --i >= 0;) {
@@ -3082,6 +3082,17 @@ merge(Compressor.prototype, {
             return trimmed && exprs;
         }
 
+        function merge_assigns(prev, defn) {
+            if (!(prev instanceof AST_SimpleStatement)) return;
+            if (declarations_only(defn)) return;
+            var exprs = extract_exprs(prev.body);
+            if (!exprs) return;
+            var definitions = [];
+            if (!join_var_assign(definitions, exprs.reverse(), 0)) return;
+            defn.definitions = definitions.reverse().concat(defn.definitions);
+            return exprs.reverse();
+        }
+
         function merge_conditional_assignments(var_def, exprs, keep) {
             if (!compressor.option("conditionals")) return;
             if (var_def.name instanceof AST_Destructured) return;
@@ -3173,9 +3184,20 @@ merge(Compressor.prototype, {
                     } else if (defs && defs.TYPE == stat.TYPE && declarations_only(stat)) {
                         defs.definitions = defs.definitions.concat(stat.definitions);
                         CHANGED = true;
+                    } else if (stat instanceof AST_Var) {
+                        var exprs = merge_assigns(prev, stat);
+                        if (exprs) {
+                            if (exprs.length) {
+                                prev.body = make_sequence(prev, exprs);
+                                j++;
+                            }
+                            CHANGED = true;
+                        } else {
+                            j++;
+                        }
+                        statements[j] = defs = stat;
                     } else {
                         statements[++j] = stat;
-                        if (stat instanceof AST_Var) defs = stat;
                     }
                     continue;
                 } else if (stat instanceof AST_Exit) {
@@ -3199,6 +3221,15 @@ merge(Compressor.prototype, {
                         CHANGED = true;
                     } else if (stat.init instanceof AST_Var) {
                         defs = stat.init;
+                        exprs = merge_assigns(prev, stat.init);
+                        if (exprs) {
+                            CHANGED = true;
+                            if (exprs.length == 0) {
+                                statements[j] = merge_defns(stat);
+                                continue;
+                            }
+                            prev.body = make_sequence(prev, exprs);
+                        }
                     }
                 } else if (stat instanceof AST_ForEnumeration) {
                     if (defs && defs.TYPE == stat.init.TYPE) {