enhance `collapse_vars` (#2952)

- `a = b, b` => `a = b`
- `a.b = c, c()` => `(a.b = c)()`

3 files changed, 721 insertions, 2 deletions

diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 60505509..d4ab444e 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -4770,3 +4770,392 @@ issue_2954_3: {
     }
     expect_stdout: Error("PASS")
 }
+
+collapse_rhs_conditional_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a = "PASS", b = "FAIL";
+        b = a;
+        "function" == typeof f && f(a);
+        console.log(a, b);
+    }
+    expect: {
+        var a = "PASS", b = "FAIL";
+        b = a;
+        "function" == typeof f && f(a);
+        console.log(a, b);
+    }
+    expect_stdout: "PASS PASS"
+}
+
+collapse_rhs_conditional_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a = "FAIL", b;
+        while ((a = "PASS", --b) && "PASS" == b);
+        console.log(a, b);
+    }
+    expect: {
+        var a = "FAIL", b;
+        while ((a = "PASS", --b) && "PASS" == b);
+        console.log(a, b);
+    }
+    expect_stdout: "PASS NaN"
+}
+
+collapse_rhs_lhs_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var c = 0;
+        new function() {
+            this[c++] = 1;
+            c += 1;
+        }();
+        console.log(c);
+    }
+    expect: {
+        var c = 0;
+        new function() {
+            this[c++] = 1;
+            c += 1;
+        }();
+        console.log(c);
+    }
+    expect_stdout: "2"
+}
+
+collapse_rhs_lhs_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var b = 1;
+        (function f(f) {
+            f = b;
+            f[b] = 0;
+        })();
+        console.log("PASS");
+    }
+    expect: {
+        var b = 1;
+        (function f(f) {
+            f = b;
+            f[b] = 0;
+        })();
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}
+
+collapse_rhs_side_effects: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a = 1, c = 0;
+        new function f() {
+            this[a-- && f()] = 1;
+            c += 1;
+        }();
+        console.log(c);
+    }
+    expect: {
+        var a = 1, c = 0;
+        new function f() {
+            this[a-- && f()] = 1;
+            c += 1;
+        }();
+        console.log(c);
+    }
+    expect_stdout: "2"
+}
+
+collapse_rhs_vardef: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b = 1;
+        a = --b + function c() {
+            var b;
+            c[--b] = 1;
+        }();
+        b |= a;
+        console.log(a, b);
+    }
+    expect: {
+        var a, b = 1;
+        a = --b + function c() {
+            var b;
+            c[--b] = 1;
+        }();
+        b |= a;
+        console.log(a, b);
+    }
+    expect_stdout: "NaN 0"
+}
+
+collapse_rhs_array: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = [];
+            b = [];
+            return [];
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            a = [];
+            b = [];
+            return [];
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "false false false"
+}
+
+collapse_rhs_boolean: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = !0;
+            b = !0;
+            return !0;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            return b = a = !0;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "true true true"
+}
+
+collapse_rhs_function: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = function() {};
+            b = function() {};
+            return function() {};
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            a = function() {};
+            b = function() {};
+            return function() {};
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "false false false"
+}
+
+collapse_rhs_number: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = 42;
+            b = 42;
+            return 42;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            return b = a = 42;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "true true true"
+}
+
+collapse_rhs_object: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = {};
+            b = {};
+            return {};
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            a = {};
+            b = {};
+            return {};
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "false false false"
+}
+
+collapse_rhs_regexp: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = /bar/;
+            b = /bar/;
+            return /bar/;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            a = /bar/;
+            b = /bar/;
+            return /bar/;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "false false false"
+}
+
+collapse_rhs_string: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = "foo";
+            b = "foo";
+            return "foo";
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            return b = a = "foo";
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "true true true"
+}
+
+collapse_rhs_var: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = f;
+            b = f;
+            return f;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            return b = a = f;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "true true true"
+}
+
+collapse_rhs_this: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = this;
+            b = this;
+            return this;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            return b = a = this;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "true true true"
+}
+
+collapse_rhs_undefined: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a, b;
+        function f() {
+            a = void 0;
+            b = void 0;
+            return void 0;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect: {
+        var a, b;
+        function f() {
+            b = a = void 0;
+            return;
+        }
+        var c = f();
+        console.log(a === b, b === c, c === a);
+    }
+    expect_stdout: "true true true"
+}
diff --git a/test/compress/pure_getters.js b/test/compress/pure_getters.js
index e2662868..f9edcc8d 100644
--- a/test/compress/pure_getters.js
+++ b/test/compress/pure_getters.js
@@ -830,3 +830,334 @@ issue_2938_4: {
     }
     expect_stdout: "PASS"
 }
+
+collapse_vars_1_true: {
+    options = {
+        collapse_vars: true,
+        pure_getters: true,
+        unused: true,
+    }
+    input: {
+        function f(a, b) {
+            for (;;) {
+                var c = a.g();
+                var d = b.p;
+                if (c || d) break;
+            }
+        }
+    }
+    expect: {
+        function f(a, b) {
+            for (;;) {
+                if (a.g() || b.p) break;
+            }
+        }
+    }
+}
+
+collapse_vars_1_false: {
+    options = {
+        collapse_vars: true,
+        pure_getters: false,
+        unused: true,
+    }
+    input: {
+        function f(a, b) {
+            for (;;) {
+                var c = a.g();
+                var d = b.p;
+                if (c || d) break;
+            }
+        }
+    }
+    expect: {
+        function f(a, b) {
+            for (;;) {
+                var c = a.g();
+                var d = b.p;
+                if (c || d) break;
+            }
+        }
+    }
+}
+
+collapse_vars_1_strict: {
+    options = {
+        collapse_vars: true,
+        pure_getters: "strict",
+        unused: true,
+    }
+    input: {
+        function f(a, b) {
+            for (;;) {
+                var c = a.g();
+                var d = b.p;
+                if (c || d) break;
+            }
+        }
+    }
+    expect: {
+        function f(a, b) {
+            for (;;) {
+                var c = a.g();
+                var d = b.p;
+                if (c || d) break;
+            }
+        }
+    }
+}
+
+collapse_vars_2_true: {
+    options = {
+        collapse_vars: true,
+        pure_getters: true,
+        reduce_vars: true,
+    }
+    input: {
+        function f() {
+            function g() {}
+            g.a = function() {};
+            g.b = g.a;
+            return g;
+        }
+    }
+    expect: {
+        function f() {
+            function g() {}
+            g.b = g.a = function() {};
+            return g;
+        }
+    }
+}
+
+collapse_vars_2_false: {
+    options = {
+        collapse_vars: true,
+        pure_getters: false,
+        reduce_vars: true,
+    }
+    input: {
+        function f() {
+            function g() {}
+            g.a = function() {};
+            g.b = g.a;
+            return g;
+        }
+    }
+    expect: {
+        function f() {
+            function g() {}
+            g.a = function() {};
+            g.b = g.a;
+            return g;
+        }
+    }
+}
+
+collapse_vars_2_strict: {
+    options = {
+        collapse_vars: true,
+        pure_getters: "strict",
+        reduce_vars: true,
+    }
+    input: {
+        function f() {
+            function g() {}
+            g.a = function() {};
+            g.b = g.a;
+            return g;
+        }
+    }
+    expect: {
+        function f() {
+            function g() {}
+            g.b = g.a = function() {};
+            return g;
+        }
+    }
+}
+
+collapse_rhs_true: {
+    options = {
+        collapse_vars: true,
+        pure_getters: true,
+    }
+    input: {
+        console.log((42..length = "PASS", "PASS"));
+        console.log(("foo".length = "PASS", "PASS"));
+        console.log((false.length = "PASS", "PASS"));
+        console.log((function() {}.length = "PASS", "PASS"));
+        console.log(({
+            get length() {
+                return "FAIL";
+            }
+        }.length = "PASS", "PASS"));
+    }
+    expect: {
+        console.log(42..length = "PASS");
+        console.log("foo".length = "PASS");
+        console.log(false.length = "PASS");
+        console.log(function() {}.length = "PASS");
+        console.log({
+            get length() {
+                return "FAIL";
+            }
+        }.length = "PASS");
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+}
+
+collapse_rhs_false: {
+    options = {
+        collapse_vars: true,
+        pure_getters: false,
+    }
+    input: {
+        console.log((42..length = "PASS", "PASS"));
+        console.log(("foo".length = "PASS", "PASS"));
+        console.log((false.length = "PASS", "PASS"));
+        console.log((function() {}.length = "PASS", "PASS"));
+        console.log(({
+            get length() {
+                return "FAIL";
+            }
+        }.length = "PASS", "PASS"));
+    }
+    expect: {
+        console.log(42..length = "PASS");
+        console.log("foo".length = "PASS");
+        console.log(false.length = "PASS");
+        console.log(function() {}.length = "PASS");
+        console.log({
+            get length() {
+                return "FAIL";
+            }
+        }.length = "PASS");
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+}
+
+collapse_rhs_strict: {
+    options = {
+        collapse_vars: true,
+        pure_getters: "strict",
+    }
+    input: {
+        console.log((42..length = "PASS", "PASS"));
+        console.log(("foo".length = "PASS", "PASS"));
+        console.log((false.length = "PASS", "PASS"));
+        console.log((function() {}.length = "PASS", "PASS"));
+        console.log(({
+            get length() {
+                return "FAIL";
+            }
+        }.length = "PASS", "PASS"));
+    }
+    expect: {
+        console.log(42..length = "PASS");
+        console.log("foo".length = "PASS");
+        console.log(false.length = "PASS");
+        console.log(function() {}.length = "PASS");
+        console.log({
+            get length() {
+                return "FAIL";
+            }
+        }.length = "PASS");
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+}
+
+collapse_rhs_setter: {
+    options = {
+        collapse_vars: true,
+        pure_getters: "strict",
+    }
+    input: {
+        try {
+            console.log(({
+                set length(v) {
+                    throw "PASS";
+                }
+            }.length = "FAIL", "FAIL"));
+        } catch (e) {
+            console.log(e);
+        }
+    }
+    expect: {
+        try {
+            console.log({
+                set length(v) {
+                    throw "PASS";
+                }
+            }.length = "FAIL");
+        } catch (e) {
+            console.log(e);
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+collapse_rhs_call: {
+    options = {
+        collapse_vars: true,
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var o = {};
+        function f() {
+            console.log("PASS");
+        }
+        o.f = f;
+        f();
+    }
+    expect: {
+        ({}.f = function() {
+            console.log("PASS");
+        })();
+    }
+    expect_stdout: "PASS"
+}
+
+collapse_rhs_lhs: {
+    options = {
+        collapse_vars: true,
+        pure_getters: true,
+    }
+    input: {
+        function f(a, b) {
+            a.b = b, b += 2;
+            console.log(a.b, b);
+        }
+        f({}, 1);
+    }
+    expect: {
+        function f(a, b) {
+            a.b = b, b += 2;
+            console.log(a.b, b);
+        }
+        f({}, 1);
+    }
+    expect_stdout: "1 3"
+}
diff --git a/test/compress/sequences.js b/test/compress/sequences.js
index 03075bf1..12acbcf7 100644
--- a/test/compress/sequences.js
+++ b/test/compress/sequences.js
@@ -668,8 +668,7 @@ side_effects_cascade_2: {
     }
     expect: {
         function f(a, b) {
-            b = a,
-            !a + (b += a) || (b += a),
+            !(b = a) + (b += a) || (b += a),
             b = a;
         }
     }