Fix JS optimizer error on ES6 spread operator (#18461)

fixes #12543

Author: pavelsavara

test/optimizer/JSDCE-output.js

@@ -14,6 +14,19 @@ function g(a) {
 
 Module["g"] = g;
 
+const sx = {
+ a: 1
+};
+
+const sar = [ 1, 2, 3 ];
+
+Module["spread"] = {
+ b: 2,
+ ...sx
+};
+
+Module["spread2"] = [ ...sar, 4, 5, 6 ];
+
 function h(a) {
  return a + 1;
 }

test/optimizer/JSDCE.js

@@ -19,6 +19,10 @@ function g(a) {
   return a+1;
 }
 Module['g'] = g;
+const sx = {a:1};
+const sar = [1,2,3];
+Module['spread'] = { b:2, ...sx };
+Module['spread2'] = [ ...sar, 4, 5, 6 ];
 
 // used
 function h(a) {

tools/acorn-optimizer.js

@@ -235,6 +235,7 @@ function hasSideEffects(node) {
       case 'VariableDeclarator':
       case 'ObjectExpression':
       case 'Property':
+      case 'SpreadElement':
       case 'BlockStatement':
       case 'ArrayExpression':
       case 'EmptyStatement': {
@@ -399,7 +400,11 @@ function runJSDCE(ast, aggressive) {
       ObjectExpression(node, c) {
         // ignore the property identifiers
         node.properties.forEach(function (node) {
-          c(node.value);
+          if (node.value) {
+            c(node.value);
+          } else if (node.argument) {
+            c(node.argument);
+          }
         });
       },
       MemberExpression(node, c) {