Added Array.from unsafe optimization (#747)

Closes #746

README.md

@@ -1090,6 +1090,7 @@ You might want to try it on your own code; it should reduce the minified size.
 Some examples of the optimizations made when this option is enabled:
 
 - `new Array(1, 2, 3)` or `Array(1, 2, 3)` → `[ 1, 2, 3 ]`
+- `Array.from([1, 2, 3])` → `[1, 2, 3]`
 - `new Object()` → `{}`
 - `String(exp)` or `exp.toString()` → `"" + exp`
 - `new Object/RegExp/Function/Error/Array (...)` → we discard the `new`

lib/compress/index.js

@@ -2058,6 +2058,14 @@ def_optimize(AST_Call, function(self, compressor) {
     }
 
     if (compressor.option("unsafe")) {
+        if (exp instanceof AST_Dot && exp.start.value === "Array" && exp.property === "from" && self.args.length === 1) {
+            const [argument] = self.args;
+            if (argument instanceof AST_Array) {
+                return make_node(AST_Array, argument, {
+                    elements: argument.elements
+                }).optimize(compressor);
+            }
+        }
         if (is_undeclared_ref(exp)) switch (exp.name) {
           case "Array":
             if (self.args.length != 1) {

test/compress/arrays.js

@@ -314,3 +314,27 @@ index_length: {
     }
     expect_stdout: "1 2"
 }
+
+array_from: {
+    options = {
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        var a = Array.from([1]);
+        var b = Array.from([1], a => a);
+        var c = Array.from(1);
+        var d = Array.from("String");
+        var e = Array.from({  });
+        console.log(a[0], b[0], c, d[3], e);
+    }
+    expect: {
+        var a = [1];
+        var b = Array.from([1], a => a);
+        var c = Array.from(1);
+        var d = Array.from("String");
+        var e = Array.from({});
+        console.log(a[0], b[0], c, d[3], e);
+    }
+    expect_stdout: "1 1 [] i []"
+}