enhance unsafe_math (#4093)

lib/compress.js

@@ -7556,13 +7556,15 @@ merge(Compressor.prototype, {
                     && self.left.is_number(compressor)) {
                     if (self.left.left instanceof AST_Constant) {
                         var lhs = make_binary(self.left, self.operator, self.left.left, self.right, self.left.left.start, self.right.end);
-                        self = make_binary(self, self.left.operator, lhs, self.left.right);
+                        self = make_binary(self, self.left.operator, try_evaluate(compressor, lhs), self.left.right);
                     } else if (self.left.right instanceof AST_Constant) {
-                        var rhs = make_binary(self.left, align(self.left.operator, self.operator), self.left.right, self.right, self.left.right.start, self.right.end);
+                        var op = align(self.left.operator, self.operator);
-                        if (self.left.operator != "-"
+                        var rhs = try_evaluate(compressor, make_binary(self.left, op, self.left.right, self.right));
-                            || !self.right.value
+                        if (rhs.is_constant()
-                            || rhs.evaluate(compressor)
+                            && !(self.left.operator == "-"
-                            || !self.left.left.is_negative_zero()) {
+                                && self.right.value != 0
+                                && +rhs.value == 0
+                                && self.left.left.is_negative_zero())) {
                             self = make_binary(self, self.left.operator, self.left.left, rhs);
                         }
                     }

test/compress/numbers.js

@@ -637,6 +637,22 @@ evaluate_7_unsafe_math: {
     ]
 }
 
+evaluate_8_unsafe_math: {
+    options = {
+        evaluate: true,
+        unsafe_math: true,
+    }
+    input: {
+        var a = [ "42" ];
+        console.log(a * (1 / 7));
+    }
+    expect: {
+        var a = [ "42" ];
+        console.log(+a / 7);
+    }
+    expect_stdout: "6"
+}
+
 NaN_redefined: {
     options = {
         evaluate: true,