compress chained compound assignments (#2850)

lib/compress.js

@@ -320,6 +320,7 @@ merge(Compressor.prototype, {
 
         function reset_def(compressor, def) {
             def.assignments = 0;
+            def.chained = false;
             def.direct_access = false;
             def.escaped = false;
             if (def.scope.uses_eval || def.scope.uses_with) {
@@ -485,19 +486,27 @@ merge(Compressor.prototype, {
         });
         def(AST_Assign, function(tw) {
             var node = this;
-            if (node.operator != "=" || !(node.left instanceof AST_SymbolRef)) return;
+            if (!(node.left instanceof AST_SymbolRef)) return;
             var d = node.left.definition();
-            if (safe_to_assign(tw, d, node.right)) {
+            var fixed = d.fixed;
-                d.references.push(node.left);
+            if (!fixed && node.operator != "=") return;
-                d.assignments++;
+            if (!safe_to_assign(tw, d, node.right)) return;
-                d.fixed = function() {
+            d.references.push(node.left);
-                    return node.right;
+            d.assignments++;
-                };
+            if (node.operator != "=") d.chained = true;
-                mark(tw, d, false);
+            d.fixed = node.operator == "=" ? function() {
-                node.right.walk(tw);
+                return node.right;
-                mark(tw, d, true);
+            } : function() {
-                return true;
+                return make_node(AST_Binary, node, {
-            }
+                    operator: node.operator.slice(0, -1),
+                    left: fixed instanceof AST_Node ? fixed : fixed(),
+                    right: node.right
+                });
+            };
+            mark(tw, d, false);
+            node.right.walk(tw);
+            mark(tw, d, true);
+            return true;
         });
         def(AST_Binary, function(tw) {
             if (!lazy_op(this.operator)) return;
@@ -672,6 +681,32 @@ merge(Compressor.prototype, {
             if (this.bfinally) this.bfinally.walk(tw);
             return true;
         });
+        def(AST_Unary, function(tw, descend) {
+            var node = this;
+            if (node.operator != "++" && node.operator != "--") return;
+            if (!(node.expression instanceof AST_SymbolRef)) return;
+            var d = node.expression.definition();
+            var fixed = d.fixed;
+            if (!fixed) return;
+            if (!safe_to_assign(tw, d, true)) return;
+            d.references.push(node.expression);
+            d.assignments++;
+            d.chained = true;
+            d.fixed = function() {
+                return make_node(AST_Binary, node, {
+                    operator: node.operator.slice(0, -1),
+                    left: make_node(AST_UnaryPrefix, node, {
+                        operator: "+",
+                        expression: fixed instanceof AST_Node ? fixed : fixed()
+                    }),
+                    right: make_node(AST_Number, node, {
+                        value: 1
+                    })
+                });
+            };
+            mark(tw, d, true);
+            return true;
+        });
         def(AST_VarDef, function(tw, descend) {
             var node = this;
             var d = node.name.definition();
@@ -2946,7 +2981,7 @@ merge(Compressor.prototype, {
                         if (def.value.has_side_effects(compressor)) {
                             def.value.walk(tw);
                         }
-                        if (def.name.fixed_value() === def.value) {
+                        if (!node_def.chained && def.name.fixed_value() === def.value) {
                             fixed_ids[node_def.id] = def;
                         }
                     }
@@ -3164,7 +3199,7 @@ merge(Compressor.prototype, {
                 && self.variables.get(sym.name) === (node_def = sym.definition())) {
                 if (node instanceof AST_Assign) {
                     node.right.walk(tw);
-                    if (node.left.fixed_value() === node.right) {
+                    if (!node_def.chained && node.left.fixed_value() === node.right) {
                         fixed_ids[node_def.id] = node;
                     }
                 }

test/compress/collapse_vars.js

@@ -52,13 +52,8 @@ collapse_vars_side_effects_1: {
             console.log.bind(console)(s.charAt(i++), s.charAt(i++), s.charAt(i++), 7);
         }
         function f2() {
-            var log = console.log.bind(console),
+            var s = "abcdef", i = 2;
-                s = "abcdef",
+            console.log.bind(console)(s.charAt(i++), 5, s.charAt(i++), s.charAt(i++), 7);
-                i = 2,
-                x = s.charAt(i++),
-                y = s.charAt(i++),
-                z = s.charAt(i++);
-            log(x, i, y, z, 7);
         }
         function f3() {
             var s = "abcdef",
@@ -72,7 +67,7 @@ collapse_vars_side_effects_1: {
             var i = 10,
                 x = i += 2,
                 y = i += 3;
-            console.log.bind(console)(x, i += 4, y, i);
+            console.log.bind(console)(x, i += 4, y, 19);
         }
         f1(), f2(), f3(), f4();
     }

test/compress/reduce_vars.js

@@ -76,14 +76,12 @@ modified: {
             console.log(a + 1);
             console.log(b + 1);
         }
-
         function f1() {
             var a = 1, b = 2;
             --b;
             console.log(a + 1);
             console.log(b + 1);
         }
-
         function f2() {
             var a = 1, b = 2, c = 3;
             b = c;
@@ -92,7 +90,6 @@ modified: {
             console.log(a + c);
             console.log(a + b + c);
         }
-
         function f3() {
             var a = 1, b = 2, c = 3;
             b *= c;
@@ -101,7 +98,6 @@ modified: {
             console.log(a + c);
             console.log(a + b + c);
         }
-
         function f4() {
             var a = 1, b = 2, c = 3;
             if (a) {
@@ -114,28 +110,26 @@ modified: {
             console.log(a + c);
             console.log(a + b + c);
         }
-
         function f5(a) {
             B = a;
-            console.log(A ? 'yes' : 'no');
+            console.log(typeof A ? "yes" : "no");
-            console.log(B ? 'yes' : 'no');
+            console.log(typeof B ? "yes" : "no");
         }
+        f0(), f1(), f2(), f3(), f4(), f5();
     }
     expect: {
         function f0() {
             var b = 2;
             b++;
             console.log(2);
-            console.log(b + 1);
+            console.log(4);
         }
-
         function f1() {
             var b = 2;
             --b;
             console.log(2);
-            console.log(b + 1);
+            console.log(2);
         }
-
         function f2() {
             3;
             console.log(4);
@@ -143,16 +137,14 @@ modified: {
             console.log(4);
             console.log(7);
         }
-
         function f3() {
             var b = 2;
             b *= 3;
-            console.log(1 + b);
+            console.log(7);
-            console.log(b + 3);
+            console.log(9);
             console.log(4);
-            console.log(1 + b + 3);
+            console.log(10);
         }
-
         function f4() {
             var b = 2, c = 3;
             b = c;
@@ -161,13 +153,33 @@ modified: {
             console.log(1 + c);
             console.log(1 + b + c);
         }
-
         function f5(a) {
             B = a;
-            console.log(A ? 'yes' : 'no');
+            console.log(typeof A ? "yes" : "no");
-            console.log(B ? 'yes' : 'no');
+            console.log(typeof B ? "yes" : "no");
         }
+        f0(), f1(), f2(), f3(), f4(), f5();
     }
+    expect_stdout: [
+        "2",
+        "4",
+        "2",
+        "2",
+        "4",
+        "6",
+        "4",
+        "7",
+        "7",
+        "9",
+        "4",
+        "10",
+        "4",
+        "6",
+        "4",
+        "7",
+        "yes",
+        "yes",
+    ]
 }
 
 unsafe_evaluate: {
@@ -745,7 +757,7 @@ iife: {
     expect: {
         !function(a, b, c) {
             b++;
-            console.log(0, 1 * b, 5);
+            console.log(0, 3, 5);
         }(1, 2, 3);
     }
     expect_stdout: true
@@ -766,7 +778,7 @@ iife_new: {
     expect: {
         var A = new function(a, b, c) {
             b++;
-            console.log(0, 1 * b, 5);
+            console.log(0, 3, 5);
         }(1, 2, 3);
     }
     expect_stdout: true
@@ -5383,3 +5395,43 @@ issue_2836: {
     }
     expect_stdout: "PASS"
 }
+
+lvalues_def_1: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var b = 1;
+        var a = b++, b = NaN;
+        console.log(a, b);
+    }
+    expect: {
+        var b = 1;
+        var a = b++;
+        b = NaN;
+        console.log(a, b);
+    }
+    expect_stdout: "1 NaN"
+}
+
+lvalues_def_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var b = 1;
+        var a = b += 1, b = NaN;
+        console.log(a, b);
+    }
+    expect: {
+        var b = 1;
+        var a = b += 1;
+        b = NaN;
+        console.log(a, b);
+    }
+    expect_stdout: "2 NaN"
+}