enhance if_return (#5518)

lib/compress.js

@@ -3391,6 +3391,7 @@ Compressor.prototype.compress = function(node) {
             var changed = false;
             var parent = compressor.parent();
             var self = compressor.self();
+            var exit, exit_defs, merge_exit;
             var in_iife = in_lambda && parent && parent.TYPE == "Call" && parent.expression === self;
             var chain_if_returns = in_lambda && compressor.option("conditionals") && compressor.option("sequences");
             var multiple_if_returns = has_multiple_if_returns(statements);
@@ -3446,6 +3447,7 @@ Compressor.prototype.compress = function(node) {
                             stat.condition = cond;
                             statements[j] = stat.body;
                             stat.body = next;
+                            if (next === exit) exit = null;
                             statements[i] = stat;
                             statements[i] = stat.transform(compressor);
                             continue;
@@ -3489,6 +3491,7 @@ Compressor.prototype.compress = function(node) {
                         changed = true;
                         stat = stat.clone();
                         stat.alternative = next;
+                        if (next === exit) exit = null;
                         statements.splice(i, 1, stat.transform(compressor));
                         statements.splice(j, 1);
                         continue;
@@ -3532,6 +3535,11 @@ Compressor.prototype.compress = function(node) {
                         continue;
                     }
                 }
+
+                if (stat instanceof AST_Exit) {
+                    exit = stat;
+                    exit_defs = null;
+                }
             }
             return changed;
 
@@ -3553,7 +3561,25 @@ Compressor.prototype.compress = function(node) {
             }
 
             function can_drop_abort(ab) {
-                if (ab instanceof AST_Return) return in_lambda && is_undefined(ab.value);
+                if (ab instanceof AST_Exit) {
+                    if (exit && exit.equivalent_to(ab)) {
+                        if (!exit_defs) {
+                            exit_defs = new Dictionary();
+                            exit.walk(new TreeWalker(function(node) {
+                                if (node instanceof AST_SymbolRef) exit_defs.set(node.name, node.definition());
+                            }));
+                        }
+                        var abort = false;
+                        ab.walk(new TreeWalker(function(node) {
+                            if (abort) return true;
+                            if (node instanceof AST_SymbolRef && exit_defs.get(node.name) !== node.definition()) {
+                                return abort = true;
+                            }
+                        }));
+                        if (!abort) return merge_exit = true;
+                    }
+                    return in_lambda && ab instanceof AST_Return && is_undefined(ab.value);
+                }
                 if (!(ab instanceof AST_LoopControl)) return false;
                 var lct = compressor.loopcontrol_target(ab);
                 if (ab instanceof AST_Continue) return match_target(loop_body(lct));
@@ -3562,6 +3588,7 @@ Compressor.prototype.compress = function(node) {
             }
 
             function can_merge_flow(ab) {
+                merge_exit = false;
                 if (!can_drop_abort(ab)) return false;
                 for (var j = statements.length; --j > i;) {
                     var stat = statements[j];
@@ -3581,7 +3608,16 @@ Compressor.prototype.compress = function(node) {
             function extract_functions() {
                 var defuns = [];
                 var lexical = false;
-                var tail = statements.splice(i + 1).filter(function(stat) {
+                var start = i + 1;
+                var end;
+                if (merge_exit) {
+                    end = statements.lastIndexOf(exit);
+                    if (end < 0) end = statements.length;
+                } else {
+                    end = statements.length;
+                    exit = null;
+                }
+                var tail = statements.splice(start, end - start).filter(function(stat) {
                     if (stat instanceof AST_LambdaDefinition) {
                         defuns.push(stat);
                         return false;
@@ -3600,7 +3636,7 @@ Compressor.prototype.compress = function(node) {
                     block = last.body;
                 }
                 block.pop();
-                if (ab.value) block.push(make_node(AST_SimpleStatement, ab.value, { body: ab.value }));
+                if (!merge_exit && ab.value) block.push(make_node(AST_SimpleStatement, ab.value, { body: ab.value }));
                 return body;
             }
 

test/compress/if_return.js

@@ -850,3 +850,116 @@ issue_866_2: {
         })();
     }
 }
+
+identical_returns_1: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        console.log(function() {
+            if (console.log("foo"))
+                return 42;
+            else
+                while (console.log("bar"));
+            return 42;
+        }());
+    }
+    expect: {
+        console.log(function() {
+            if (!console.log("foo"))
+                while (console.log("bar"));
+            return 42;
+        }());
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+        "42",
+    ]
+}
+
+identical_returns_2: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        console.log(function() {
+            if (console.log("foo"))
+                while (console.log("FAIL"));
+            else
+                return "bar";
+            return "bar";
+        }());
+    }
+    expect: {
+        console.log(function() {
+            if (console.log("foo"))
+                while (console.log("FAIL"));
+            return "bar";
+        }());
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+    ]
+}
+
+identical_returns_3: {
+    options = {
+        if_return: true,
+    }
+    input: {
+        function f(a) {
+            if (a)
+                return 42;
+            if (a)
+                return;
+            return 42;
+        }
+        if (f(console))
+            console.log("PASS");
+    }
+    expect: {
+        function f(a) {
+            if (a)
+                return 42;
+            if (a)
+                ;
+            else
+                return 42;
+        }
+        if (f(console))
+            console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}
+
+issue_4374: {
+    options = {
+        booleans: true,
+        conditionals: true,
+        if_return: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            console.log(f(console));
+            function f(a) {
+                if (console) return 0;
+                if (a) return 1;
+                return 0;
+            }
+        })();
+    }
+    expect: {
+        (function() {
+            console.log(function(a) {
+                return !console && a ? 1 : 0;
+            }(console));
+        })();
+    }
+    expect_stdout: "0"
+}

test/compress/let.js

@@ -892,6 +892,40 @@ if_return_2: {
     node_version: ">=4"
 }
 
+if_return_3: {
+    options = {
+        if_return: true,
+    }
+    input: {
+        "use strict";
+        var a = "PASS";
+        function f(b) {
+            if (console) {
+                let b = a;
+                return b;
+            } else
+                while (console.log("FAIL 1"));
+            return b;
+        }
+        console.log(f("FAIL 2"));
+    }
+    expect: {
+        "use strict";
+        var a = "PASS";
+        function f(b) {
+            if (console) {
+                let b = a;
+                return b;
+            } else
+                while (console.log("FAIL 1"));
+            return b;
+        }
+        console.log(f("FAIL 2"));
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
 do_if_continue_1: {
     options = {
         if_return: true,

test/compress/transform.js

@@ -127,7 +127,7 @@ if_return: {
                 if (w) {
                     if (y) return;
                 } else if (z) return;
-                return x == y || (x && w(), y && z()), !0;
+                return x != y && (x && w(), y && z()), !0;
             }
         }
     }