introduce eager evaluation (#3587)

4 files changed, 192 insertions, 45 deletions

diff --git a/README.md b/README.md
index f686889d..f86bf7ad 100644
--- a/README.md
+++ b/README.md
@@ -631,7 +631,10 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 
 - `drop_debugger` (default: `true`) -- remove `debugger;` statements
 
-- `evaluate` (default: `true`) -- attempt to evaluate constant expressions
+- `evaluate` (default: `true`) -- Evaluate expression for shorter constant
+  representation. Pass `"eager"` to always replace function calls whenever
+  possible, or a positive integer to specify an upper bound for each individual
+  evaluation in number of characters.
 
 - `expression` (default: `false`) -- Pass `true` to preserve completion values
   from terminal statements without `return`, e.g. in bookmarklets.
diff --git a/lib/compress.js b/lib/compress.js
index 9d844b81..f82a165e 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -96,6 +96,8 @@ function Compressor(options, false_by_default) {
         unsafe_undefined: false,
         unused          : !false_by_default,
     }, true);
+    var evaluate = this.options["evaluate"];
+    this.eval_threshold = /eager/.test(evaluate) ? 1 / 0 : +evaluate;
     var global_defs = this.options["global_defs"];
     if (typeof global_defs == "object") for (var key in global_defs) {
         if (/^@/.test(key) && HOP(global_defs, key)) {
@@ -2676,22 +2678,21 @@ merge(Compressor.prototype, {
         node.DEFMETHOD("_find_defs", func);
     });
 
-    function best_of_expression(ast1, ast2) {
-        return ast1.print_to_string().length >
-            ast2.print_to_string().length
-            ? ast2 : ast1;
+    function best_of_expression(ast1, ast2, threshold) {
+        var delta = ast2.print_to_string().length - ast1.print_to_string().length;
+        return delta < (threshold || 0) ? ast2 : ast1;
     }
 
-    function best_of_statement(ast1, ast2) {
+    function best_of_statement(ast1, ast2, threshold) {
         return best_of_expression(make_node(AST_SimpleStatement, ast1, {
             body: ast1
         }), make_node(AST_SimpleStatement, ast2, {
             body: ast2
-        })).body;
+        }), threshold).body;
     }
 
-    function best_of(compressor, ast1, ast2) {
-        return (first_in_statement(compressor) ? best_of_statement : best_of_expression)(ast1, ast2);
+    function best_of(compressor, ast1, ast2, threshold) {
+        return (first_in_statement(compressor) ? best_of_statement : best_of_expression)(ast1, ast2, threshold);
     }
 
     function convert_to_predicate(obj) {
@@ -2700,6 +2701,13 @@ merge(Compressor.prototype, {
         });
     }
 
+    function try_evaluate(compressor, node) {
+        var ev = node.evaluate(compressor);
+        if (ev === node) return node;
+        ev = make_node_from_constant(ev, node).optimize(compressor);
+        return best_of(compressor, node, ev, compressor.eval_threshold);
+    }
+
     var object_fns = [
         "constructor",
         "toString",
@@ -5366,12 +5374,7 @@ merge(Compressor.prototype, {
             && is_iife_call(self)) {
             return self.negate(compressor, true);
         }
-        var ev = self.evaluate(compressor);
-        if (ev !== self) {
-            ev = make_node_from_constant(ev, self).optimize(compressor);
-            return best_of(compressor, ev, self);
-        }
-        return self;
+        return try_evaluate(compressor, self);
 
         function return_value(stat) {
             if (!stat) return make_node(AST_Undefined, self);
@@ -5702,15 +5705,8 @@ merge(Compressor.prototype, {
             });
         }
         // avoids infinite recursion of numerals
-        if (self.operator != "-"
-            || !(e instanceof AST_Number || e instanceof AST_Infinity)) {
-            var ev = self.evaluate(compressor);
-            if (ev !== self) {
-                ev = make_node_from_constant(ev, self).optimize(compressor);
-                return best_of(compressor, ev, self);
-            }
-        }
-        return self;
+        return self.operator == "-" && (e instanceof AST_Number || e instanceof AST_Infinity)
+            ? self : try_evaluate(compressor, self);
     });
 
     AST_Binary.DEFMETHOD("lift_sequences", function(compressor) {
@@ -6274,12 +6270,7 @@ merge(Compressor.prototype, {
             self.right = self.right.right;
             return self.transform(compressor);
         }
-        var ev = self.evaluate(compressor);
-        if (ev !== self) {
-            ev = make_node_from_constant(ev, self).optimize(compressor);
-            return best_of(compressor, ev, self);
-        }
-        return self;
+        return try_evaluate(compressor, self);
 
         function align(ref, op) {
             switch (ref) {
@@ -6448,11 +6439,11 @@ merge(Compressor.prototype, {
                         };
                     }
                     var name_length = def.name.length;
-                    var overhead = 0;
                     if (compressor.option("unused") && !compressor.exposed(def)) {
-                        overhead = (name_length + 2 + value_length) / (def.references.length - def.assignments);
+                        name_length += (name_length + 2 + value_length) / (def.references.length - def.assignments);
                     }
-                    def.should_replace = value_length <= name_length + overhead ? fn : false;
+                    var delta = value_length - Math.floor(name_length);
+                    def.should_replace = delta < compressor.eval_threshold ? fn : false;
                 } else {
                     def.should_replace = false;
                 }
@@ -7046,12 +7037,7 @@ merge(Compressor.prototype, {
                 });
             }
         }
-        var ev = self.evaluate(compressor);
-        if (ev !== self) {
-            ev = make_node_from_constant(ev, self).optimize(compressor);
-            return best_of(compressor, ev, self);
-        }
-        return self;
+        return try_evaluate(compressor, self);
 
         function find_lambda() {
             var i = 0, p;
@@ -7152,12 +7138,7 @@ merge(Compressor.prototype, {
         }
         var sub = self.flatten_object(self.property, compressor);
         if (sub) return sub.optimize(compressor);
-        var ev = self.evaluate(compressor);
-        if (ev !== self) {
-            ev = make_node_from_constant(ev, self).optimize(compressor);
-            return best_of(compressor, ev, self);
-        }
-        return self;
+        return try_evaluate(compressor, self);
     });
 
     OPT(AST_Object, function(self, compressor) {
diff --git a/test/compress/evaluate.js b/test/compress/evaluate.js
index ea707e63..94258049 100644
--- a/test/compress/evaluate.js
+++ b/test/compress/evaluate.js
@@ -1921,3 +1921,139 @@ conditional_function: {
     }
     expect_stdout: "42 42"
 }
+
+best_of_evaluate: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function d(x, y) {
+            return x / y;
+        }
+        console.log(0 / 3, 1 / 64, 4 / 7, 7 / 7);
+        console.log(d(0, 3), d(1, 64), d(4, 7), d(7, 7));
+    }
+    expect: {
+        function d(x, y) {
+            return x / y;
+        }
+        console.log(0, 1 / 64, 4 / 7, 1);
+        console.log(0, .015625, d(4, 7), 1);
+    }
+    expect_stdout: [
+        "0 0.015625 0.5714285714285714 1",
+        "0 0.015625 0.5714285714285714 1",
+    ]
+}
+
+eager_evaluate: {
+    options = {
+        evaluate: "eager",
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function d(x, y) {
+            return x / y;
+        }
+        console.log(0 / 3, 1 / 64, 4 / 7, 7 / 7);
+        console.log(d(0, 3), d(1, 64), d(4, 7), d(7, 7));
+    }
+    expect: {
+        console.log(0, .015625, .5714285714285714, 1);
+        console.log(0, .015625, .5714285714285714, 1);
+    }
+    expect_stdout: [
+        "0 0.015625 0.5714285714285714 1",
+        "0 0.015625 0.5714285714285714 1",
+    ]
+}
+
+threshold_evaluate_default: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log(b("1"), b(2), b(b(b("ABCDEFGHIJK"))));
+    }
+    expect: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log("111", 6, b(b(b("ABCDEFGHIJK"))));
+    }
+    expect_stdout: "111 6 ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK"
+}
+
+threshold_evaluate_30: {
+    options = {
+        evaluate: 30,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log(b("1"), b(2), b(b(b("ABCDEFGHIJK"))));
+    }
+    expect: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log("111", 6, b(b("ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK")));
+    }
+    expect_stdout: "111 6 ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK"
+}
+
+threshold_evaluate_100: {
+    options = {
+        evaluate: 100,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log(b("1"), b(2), b(b(b("ABCDEFGHIJK"))));
+    }
+    expect: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log("111", 6, b("ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK"));
+    }
+    expect_stdout: "111 6 ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK"
+}
+
+threshold_evaluate_999: {
+    options = {
+        evaluate: 999,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function b(x) {
+            return x + x + x;
+        }
+        console.log(b("1"), b(2), b(b(b("ABCDEFGHIJK"))));
+    }
+    expect: {
+        console.log("111", 6, "ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK");
+    }
+    expect_stdout: "111 6 ABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJKABCDEFGHIJK"
+}
diff --git a/test/compress/issue-1609.js b/test/compress/issue-1609.js
index d8e82263..17fbb0e7 100644
--- a/test/compress/issue-1609.js
+++ b/test/compress/issue-1609.js
@@ -52,3 +52,30 @@ chained_evaluation_2: {
         })();
     }
 }
+
+chained_evaluation_3: {
+    options = {
+        collapse_vars: true,
+        evaluate: 10,
+        reduce_funcs: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            var a = "long piece of string";
+            (function() {
+                var b = a, c;
+                c = f(b);
+                c.bar = b;
+            })();
+        })();
+    }
+    expect: {
+        (function() {
+            (function() {
+                f("long piece of string").bar = "long piece of string";
+            })();
+        })();
+    }
+}