From a478f275e421ccbb428f38272e8e673f6684729c Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Tue, 28 Jan 2020 09:58:01 +0800
Subject: enhance `sequences` (#3693)

---
 lib/compress.js | 82 ++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 46 insertions(+), 36 deletions(-)

(limited to 'lib')

diff --git a/lib/compress.js b/lib/compress.js
index e14d9d06..2a338ba1 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -5400,25 +5400,32 @@ merge(Compressor.prototype, {
         return self.definitions.length ? self : make_node(AST_EmptyStatement, self);
     });
 
-    AST_Call.DEFMETHOD("lift_sequences", function(compressor) {
-        if (!compressor.option("sequences")) return this;
-        var exp = this.expression;
-        if (!(exp instanceof AST_Sequence)) return this;
-        var tail = exp.tail_node();
-        if (needs_unbinding(compressor, tail) && !(this instanceof AST_New)) return this;
-        var expressions = exp.expressions.slice(0, -1);
-        var node = this.clone();
-        node.expression = tail;
-        expressions.push(node);
-        return make_sequence(this, expressions).optimize(compressor);
-    });
+    function lift_sequence_in_expression(node, compressor) {
+        var exp = node.expression;
+        if (!(exp instanceof AST_Sequence)) return node;
+        var x = exp.expressions.slice();
+        var e = node.clone();
+        e.expression = x.pop();
+        x.push(e);
+        return make_sequence(node, x);
+    }
 
     OPT(AST_Call, function(self, compressor) {
-        var seq = self.lift_sequences(compressor);
-        if (seq !== self) {
-            return seq;
-        }
         var exp = self.expression;
+        if (compressor.option("sequences")) {
+            if (exp instanceof AST_PropAccess) {
+                var seq = lift_sequence_in_expression(exp, compressor);
+                if (seq !== exp) {
+                    var call = self.clone();
+                    call.expression = seq.expressions.pop();
+                    seq.expressions.push(call);
+                    return seq.optimize(compressor);
+                }
+            } else if (!needs_unbinding(compressor, exp.tail_node())) {
+                var seq = lift_sequence_in_expression(self, compressor);
+                if (seq !== self) return seq.optimize(compressor);
+            }
+        }
         var fn = exp;
         if (compressor.option("reduce_vars") && fn instanceof AST_SymbolRef) {
             fn = fn.fixed_value();
@@ -5989,9 +5996,9 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_New, function(self, compressor) {
-        var seq = self.lift_sequences(compressor);
-        if (seq !== self) {
-            return seq;
+        if (compressor.option("sequences")) {
+            var seq = lift_sequence_in_expression(self, compressor);
+            if (seq !== self) return seq.optimize(compressor);
         }
         if (compressor.option("unsafe")) {
             var exp = self.expression;
@@ -6047,19 +6054,12 @@ merge(Compressor.prototype, {
         }
     });
 
-    AST_Unary.DEFMETHOD("lift_sequences", function(compressor) {
-        if (compressor.option("sequences") && this.expression instanceof AST_Sequence) {
-            var x = this.expression.expressions.slice();
-            var e = this.clone();
-            e.expression = x.pop();
-            x.push(e);
-            return make_sequence(this, x).optimize(compressor);
-        }
-        return this;
-    });
-
     OPT(AST_UnaryPostfix, function(self, compressor) {
-        return self.lift_sequences(compressor);
+        if (compressor.option("sequences")) {
+            var seq = lift_sequence_in_expression(self, compressor);
+            if (seq !== self) return seq.optimize(compressor);
+        }
+        return self;
     });
 
     OPT(AST_UnaryPrefix, function(self, compressor) {
@@ -6076,9 +6076,9 @@ merge(Compressor.prototype, {
             }
             return make_sequence(self, [ e, make_node(AST_True, self) ]).optimize(compressor);
         }
-        var seq = self.lift_sequences(compressor);
-        if (seq !== self) {
-            return seq;
+        if (compressor.option("sequences")) {
+            var seq = lift_sequence_in_expression(self, compressor);
+            if (seq !== self) return seq.optimize(compressor);
         }
         if (compressor.option("side_effects") && self.operator == "void") {
             e = e.drop_side_effect_free(compressor);
@@ -6211,7 +6211,8 @@ merge(Compressor.prototype, {
             // result.  hence, force switch.
             reverse();
         }
-        self = self.lift_sequences(compressor);
+        var seq = self.lift_sequences(compressor);
+        if (seq !== self) return seq;
         if (compressor.option("assignments") && lazy_op[self.operator]) {
             var assign = self.right;
             // a || (a = x) => a = a || x
@@ -7127,7 +7128,8 @@ merge(Compressor.prototype, {
                     || parent instanceof AST_UnaryPrefix);
             }
         }
-        self = self.lift_sequences(compressor);
+        var seq = self.lift_sequences(compressor);
+        if (seq !== self) return seq;
         if (!compressor.option("assignments")) return self;
         if (self.operator == "=" && self.left instanceof AST_SymbolRef && self.right instanceof AST_Binary) {
             // x = expr1 OP expr2
@@ -7486,6 +7488,10 @@ merge(Compressor.prototype, {
     }
 
     OPT(AST_Sub, function(self, compressor) {
+        if (compressor.option("sequences") && compressor.parent().TYPE != "Call") {
+            var seq = lift_sequence_in_expression(self, compressor);
+            if (seq !== self) return seq.optimize(compressor);
+        }
         var expr = self.expression;
         var prop = self.property;
         if (compressor.option("properties")) {
@@ -7650,6 +7656,10 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_Dot, function(self, compressor) {
+        if (compressor.option("sequences") && compressor.parent().TYPE != "Call") {
+            var seq = lift_sequence_in_expression(self, compressor);
+            if (seq !== self) return seq.optimize(compressor);
+        }
         if (self.property == "arguments" || self.property == "caller") {
             AST_Node.warn("Function.prototype.{prop} not supported [{file}:{line},{col}]", {
                 prop: self.property,
-- 
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