Optimize rest parameter emit microsoft#19182

Author: charlespierce

src/compiler/transformers/es2015.ts

@@ -944,7 +944,6 @@ namespace ts {
 
             if (constructor) {
                 addDefaultValueAssignmentsIfNeeded(statements, constructor);
-                addRestParameterIfNeeded(statements, constructor, hasSynthesizedSuper);
                 if (!hasSynthesizedSuper) {
                     // If no super call has been synthesized, emit custom prologue directives.
                     statementOffset = addCustomPrologue(statements, constructor.body.statements, statementOffset, visitor);
@@ -969,6 +968,7 @@ namespace ts {
                 }
 
                 addRange(statements, visitNodes(constructor.body.statements, visitor, isStatement, /*start*/ statementOffset));
+                insertRestParameterIfNeeded(statements, constructor, hasSynthesizedSuper);
             }
 
             // Return `_this` unless we're sure enough that it would be pointless to add a return statement.
@@ -1344,6 +1344,38 @@ namespace ts {
             return node && node.dotDotDotToken && node.name.kind === SyntaxKind.Identifier && !inConstructorWithSynthesizedSuper;
         }
 
+        /**
+         * Gets the index of the first statement that contains a reference to a given parameter
+         *
+         * @param restParameter The ParameterDeclaration to which we are finding references.
+         * @param statements An array of Statement nodes to search
+         */
+        function findRestParameterReferenceIndex(restParameter: ParameterDeclaration, statements: Statement[]) {
+            const originalRestParameter = getOriginalNode(restParameter);
+
+            return findIndex(statements, containsReferenceToParameter);
+
+            function containsReferenceToParameter(statement: Statement): boolean {
+                return (isIdentifier(statement) && originalRestParameter === resolver.getReferencedValueDeclaration(statement)) ||
+                    forEachChild(statement, containsReferenceToParameter);
+            }
+        }
+
+        /**
+         * Gets the index of the first statement that contains a re-definition of "arguments"
+         *
+         * @param statements An array of Statement nodes to search
+         */
+        function findArgumentsRedefinitionIndex(statements: Statement[]) {
+            return findIndex(statements, containsArgumentsRedeclaration);
+
+            function containsArgumentsRedeclaration(statement: Statement): boolean {
+                return (isAssignmentExpression(statement) && isIdentifier(statement.left) && statement.left.escapedText === "arguments") ||
+                    (isVariableDeclaration(statement) && statement.initializer && (<Identifier>statement.name).escapedText === "arguments") ||
+                    forEachChild(statement, containsArgumentsRedeclaration);
+            }
+        }
+
         /**
          * Adds statements to the body of a function-like node if it contains a rest parameter.
          *
@@ -1353,12 +1385,23 @@ namespace ts {
          *                                          part of a constructor declaration with a
          *                                          synthesized call to `super`
          */
-        function addRestParameterIfNeeded(statements: Statement[], node: FunctionLikeDeclaration, inConstructorWithSynthesizedSuper: boolean): void {
+        function insertRestParameterIfNeeded(statements: Statement[], node: FunctionLikeDeclaration, inConstructorWithSynthesizedSuper: boolean): void {
             const parameter = lastOrUndefined(node.parameters);
             if (!shouldAddRestParameter(parameter, inConstructorWithSynthesizedSuper)) {
                 return;
             }
 
+            let referenceIndex = findRestParameterReferenceIndex(parameter, statements);
+            if (referenceIndex === -1) {
+                return;
+            }
+
+            const argumentsRedefinitionIndex = findArgumentsRedefinitionIndex(statements);
+            if (argumentsRedefinitionIndex > -1) {
+                // If the "arguments" variable is redefined, need to make sure to emit the rest parameter initialization before then.
+                referenceIndex = Math.min(referenceIndex, argumentsRedefinitionIndex);
+            }
+
             // `declarationName` is the name of the local declaration for the parameter.
             const declarationName = getMutableClone(<Identifier>parameter.name);
             setEmitFlags(declarationName, EmitFlags.NoSourceMap);
@@ -1369,9 +1412,7 @@ namespace ts {
             const temp = createLoopVariable();
 
             // var param = [];
-            statements.push(
-                setEmitFlags(
-                    setTextRange(
+            const variableStatement = setTextRange(
                         createVariableStatement(
                             /*modifiers*/ undefined,
                             createVariableDeclarationList([
@@ -1383,10 +1424,7 @@ namespace ts {
                             ])
                         ),
                         /*location*/ parameter
-                    ),
-                    EmitFlags.CustomPrologue
-                )
-            );
+                    );
 
             // for (var _i = restIndex; _i < arguments.length; _i++) {
             //   param[_i - restIndex] = arguments[_i];
@@ -1426,9 +1464,8 @@ namespace ts {
                 ])
             );
 
-            setEmitFlags(forStatement, EmitFlags.CustomPrologue);
             startOnNewLine(forStatement);
-            statements.push(forStatement);
+            statements.splice(referenceIndex, 0, variableStatement, forStatement);
         }
 
         /**
@@ -1846,7 +1883,6 @@ namespace ts {
 
             addCaptureThisForNodeIfNeeded(statements, node);
             addDefaultValueAssignmentsIfNeeded(statements, node);
-            addRestParameterIfNeeded(statements, node, /*inConstructorWithSynthesizedSuper*/ false);
 
             // If we added any generated statements, this must be a multi-line block.
             if (!multiLine && statements.length > 0) {
@@ -1895,13 +1931,16 @@ namespace ts {
                 closeBraceLocation = body;
             }
 
+            const statementBodyLength = statements.length;
+            insertRestParameterIfNeeded(statements, node, /*inConstructorWithSynthesizedSuper*/ false);
+
             const lexicalEnvironment = context.endLexicalEnvironment();
             addRange(statements, lexicalEnvironment);
 
             prependCaptureNewTargetIfNeeded(statements, node, /*copyOnWrite*/ false);
 
             // If we added any final generated statements, this must be a multi-line block
-            if (!multiLine && lexicalEnvironment && lexicalEnvironment.length) {
+            if (!multiLine && statements.length !== statementBodyLength) {
                 multiLine = true;
             }
 

tests/baselines/reference/accessorWithRestParam.js

@@ -9,22 +9,12 @@ var C = /** @class */ (function () {
     function C() {
     }
     Object.defineProperty(C.prototype, "X", {
-        set: function () {
-            var v = [];
-            for (var _i = 0; _i < arguments.length; _i++) {
-                v[_i] = arguments[_i];
-            }
-        },
+        set: function () { },
         enumerable: true,
         configurable: true
     });
     Object.defineProperty(C, "X", {
-        set: function () {
-            var v2 = [];
-            for (var _i = 0; _i < arguments.length; _i++) {
-                v2[_i] = arguments[_i];
-            }
-        },
+        set: function () { },
         enumerable: true,
         configurable: true
     });

tests/baselines/reference/arrayLiteralInNonVarArgParameter.js

@@ -5,10 +5,5 @@ panic([], 'one', 'two');
 
 
 //// [arrayLiteralInNonVarArgParameter.js]
-function panic(val) {
-    var opt = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        opt[_i - 1] = arguments[_i];
-    }
-}
+function panic(val) { }
 panic([], 'one', 'two');

tests/baselines/reference/assignmentCompatWithCallSignaturesWithRestParameters.js

@@ -49,49 +49,19 @@ var a4: (x?: number, y?: string, ...z: number[]) => number;
 // call signatures in derived types must have the same or fewer optional parameters as the target for assignment
 var a; // ok, same number of required params
 a = function () { return 1; }; // ok, same number of required params
-a = function () {
-    var args = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        args[_i] = arguments[_i];
-    }
-    return 1;
-}; // ok, same number of required params
-a = function () {
-    var args = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        args[_i] = arguments[_i];
-    }
-    return 1;
-}; // error, type mismatch
+a = function () { return 1; }; // ok, same number of required params
+a = function () { return 1; }; // error, type mismatch
 a = function (x) { return 1; }; // ok, same number of required params
 a = function (x, y, z) { return 1; }; // ok, same number of required params
 a = function (x) { return 1; }; // ok, rest param corresponds to infinite number of params
 a = function (x) { return 1; }; // error, incompatible type
 var a2;
 a2 = function () { return 1; }; // ok, fewer required params
-a2 = function () {
-    var args = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        args[_i] = arguments[_i];
-    }
-    return 1;
-}; // ok, fewer required params
+a2 = function () { return 1; }; // ok, fewer required params
 a2 = function (x) { return 1; }; // ok, fewer required params
 a2 = function (x) { return 1; }; // ok, same number of required params
-a2 = function (x) {
-    var args = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        args[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // ok, same number of required params
-a2 = function (x) {
-    var args = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        args[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // should be type mismatch error
+a2 = function (x) { return 1; }; // ok, same number of required params
+a2 = function (x) { return 1; }; // should be type mismatch error
 a2 = function (x, y) { return 1; }; // ok, rest param corresponds to infinite number of params
 a2 = function (x, y) { return 1; }; // ok, same number of required params
 var a3;
@@ -100,24 +70,12 @@ a3 = function (x) { return 1; }; // ok, fewer required params
 a3 = function (x) { return 1; }; // ok, same number of required params
 a3 = function (x, y) { return 1; }; // ok, all present params match
 a3 = function (x, y, z) { return 1; }; // error
-a3 = function (x) {
-    var z = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        z[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // error
+a3 = function (x) { return 1; }; // error
 a3 = function (x, y, z) { return 1; }; // error
 var a4;
 a4 = function () { return 1; }; // ok, fewer required params
 a4 = function (x, y) { return 1; }; // error, type mismatch
 a4 = function (x) { return 1; }; // ok, all present params match
 a4 = function (x, y) { return 1; }; // error, second param has type mismatch
 a4 = function (x, y) { return 1; }; // ok, same number of required params with matching types
-a4 = function (x) {
-    var args = [];
-    for (var _i = 1; _i < arguments.length; _i++) {
-        args[_i - 1] = arguments[_i];
-    }
-    return 1;
-}; // error, rest params have type mismatch
+a4 = function (x) { return 1; }; // error, rest params have type mismatch

tests/baselines/reference/baseTypeAfterDerivedType.js

@@ -20,11 +20,6 @@ interface Base2 {
 var Derived2 = /** @class */ (function () {
     function Derived2() {
     }
-    Derived2.prototype.method = function () {
-        var args = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            args[_i] = arguments[_i];
-        }
-    };
+    Derived2.prototype.method = function () { };
     return Derived2;
 }());

tests/baselines/reference/callWithSpread.js

@@ -70,10 +70,6 @@ var __extends = (this && this.__extends) || (function () {
     };
 })();
 function foo(x, y) {
-    var z = [];
-    for (var _i = 2; _i < arguments.length; _i++) {
-        z[_i - 2] = arguments[_i];
-    }
 }
 var a;
 var z;
@@ -100,18 +96,14 @@ xa[1].foo(1, 2, "abc");
 (_g = xa[1]).foo.apply(_g, [1, 2, "abc"]);
 var C = /** @class */ (function () {
     function C(x, y) {
+        this.foo(x, y);
         var z = [];
         for (var _i = 2; _i < arguments.length; _i++) {
             z[_i - 2] = arguments[_i];
         }
-        this.foo(x, y);
         this.foo.apply(this, [x, y].concat(z));
     }
     C.prototype.foo = function (x, y) {
-        var z = [];
-        for (var _i = 2; _i < arguments.length; _i++) {
-            z[_i - 2] = arguments[_i];
-        }
     };
     return C;
 }());

tests/baselines/reference/capturedLetConstInLoop13.js

@@ -29,17 +29,17 @@ var Main = /** @class */ (function () {
     }
     Main.prototype.register = function () {
         var _this = this;
-        var names = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            names[_i] = arguments[_i];
-        }
         var _loop_1 = function (name) {
             this_1.bar((_a = {},
                 _a[name + ".a"] = function () { _this.foo(name); },
                 _a));
             var _a;
         };
         var this_1 = this;
+        var names = [];
+        for (var _i = 0; _i < arguments.length; _i++) {
+            names[_i] = arguments[_i];
+        }
         for (var _a = 0, names_1 = names; _a < names_1.length; _a++) {
             var name = names_1[_a];
             _loop_1(name);

tests/baselines/reference/checkSuperCallBeforeThisAccessing5.js

@@ -20,10 +20,6 @@ var __extends = (this && this.__extends) || (function () {
 })();
 var Based = /** @class */ (function () {
     function Based() {
-        var arg = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            arg[_i] = arguments[_i];
-        }
     }
     return Based;
 }());

tests/baselines/reference/checkSuperCallBeforeThisAccessing6.js

@@ -23,10 +23,6 @@ var __extends = (this && this.__extends) || (function () {
 })();
 var Base = /** @class */ (function () {
     function Base() {
-        var arg = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            arg[_i] = arguments[_i];
-        }
     }
     return Base;
 }());

tests/baselines/reference/checkSuperCallBeforeThisAccessing8.js

@@ -23,10 +23,6 @@ var __extends = (this && this.__extends) || (function () {
 })();
 var Base = /** @class */ (function () {
     function Base() {
-        var arg = [];
-        for (var _i = 0; _i < arguments.length; _i++) {
-            arg[_i] = arguments[_i];
-        }
     }
     return Base;
 }());