Bug 1830727 - Emit JSOp::IsNullOrUndefined for null-or-undefined checks in self-hosted code. r=iain

It's fairly common in the JS spec to check whether a value is null-or-undefined.
We already have a bytecode op for this that we can use if we add an `IsNullOrUndefined`
intrinsic.

This has some minor performance benefits (no Baseline ICs instead of 3 Baseline ICs)
and no `Or` or `And` branch, but it also makes our bytecode more compact. This will
help with follow-up work to look into inlining more string builtins.

Differential Revision: https://phabricator.services.mozilla.com/D176902

js/src/builtin/.eslintrc.js

@@ -136,6 +136,7 @@ module.exports = {
         SetIsInlinableLargeFunction: "readonly",
         ToNumeric: "readonly",
         ToString: "readonly",
+        IsNullOrUndefined: "readonly",
 
         // We've disabled all built-in environments, which also removed
         // `undefined` from the list of globals. Put it back because it's

js/src/builtin/Array.js

@@ -1024,7 +1024,7 @@ function ArrayFrom(items, mapfn = undefined, thisArg = undefined) {
 
   // Step 5.
   // Inlined: GetMethod, step 3.
-  if (usingIterator !== undefined && usingIterator !== null) {
+  if (!IsNullOrUndefined(usingIterator)) {
     // Inlined: GetMethod, step 4.
     if (!IsCallable(usingIterator)) {
       ThrowTypeError(JSMSG_NOT_ITERABLE, DecompileArg(0, items));
@@ -1135,7 +1135,7 @@ function ArrayToLocaleString(locales, options) {
 
   // Steps 6-7.
   var R;
-  if (firstElement === undefined || firstElement === null) {
+  if (IsNullOrUndefined(firstElement)) {
     R = "";
   } else {
 #if JS_HAS_INTL_API
@@ -1165,7 +1165,7 @@ function ArrayToLocaleString(locales, options) {
 
     // Steps 9.a, 9.c-e.
     R += separator;
-    if (!(nextElement === undefined || nextElement === null)) {
+    if (!IsNullOrUndefined(nextElement)) {
 #if JS_HAS_INTL_API
       R += ToString(
         callContentFunction(

js/src/builtin/AsyncIteration.js

@@ -37,7 +37,7 @@ async function AsyncIteratorClose(iteratorRecord, value) {
   // Step 4.
   const returnMethod = iterator.return;
   // Step 5.
-  if (returnMethod !== undefined && returnMethod !== null) {
+  if (!IsNullOrUndefined(returnMethod)) {
     const result = await callContentFunction(returnMethod, iterator);
     // Step 8.
     if (!IsObject(result)) {
@@ -74,7 +74,7 @@ function GetAsyncIteratorDirectWrapper(obj) {
     },
     async return(value) {
       const returnMethod = obj.return;
-      if (returnMethod !== undefined && returnMethod !== null) {
+      if (!IsNullOrUndefined(returnMethod)) {
         return callContentFunction(returnMethod, obj, value);
       }
       return { done: true, value };

js/src/builtin/Iterator.js

@@ -32,7 +32,7 @@ function IteratorClose(iteratorRecord, value) {
   // Step 4.
   const returnMethod = iterator.return;
   // Step 5.
-  if (returnMethod !== undefined && returnMethod !== null) {
+  if (!IsNullOrUndefined(returnMethod)) {
     const result = callContentFunction(returnMethod, iterator);
     // Step 8.
     if (!IsObject(result)) {
@@ -124,7 +124,7 @@ function GetIteratorDirectWrapper(obj) {
     },
     return(value) {
       const returnMethod = obj.return;
-      if (returnMethod !== undefined && returnMethod !== null) {
+      if (!IsNullOrUndefined(returnMethod)) {
         return callContentFunction(returnMethod, obj, value);
       }
       return { done: true, value };
@@ -165,7 +165,7 @@ function IteratorFrom(O) {
 
   let iteratorRecord;
   // Step 2.
-  if (usingIterator !== undefined && usingIterator !== null) {
+  if (!IsNullOrUndefined(usingIterator)) {
     // Step a.
     // Inline call to GetIterator.
     const iterator = callContentFunction(usingIterator, O);
@@ -240,7 +240,7 @@ function WrapForValidIteratorReturn(value) {
   // Inline call to IteratorClose.
   const iterator = iterated.iterator;
   const returnMethod = iterator.return;
-  if (returnMethod !== undefined && returnMethod !== null) {
+  if (!IsNullOrUndefined(returnMethod)) {
     let innerResult = callContentFunction(returnMethod, iterator);
     if (!IsObject(innerResult)) {
       ThrowTypeError(JSMSG_OBJECT_REQUIRED, DecompileArg(0, innerResult));
@@ -271,7 +271,7 @@ function WrapForValidIteratorThrow(value) {
   // Step 4.
   const throwMethod = iterator.throw;
   // Step 5.
-  if (throwMethod === undefined || throwMethod === null) {
+  if (IsNullOrUndefined(throwMethod)) {
     throw value;
   }
   // Step 6.

js/src/builtin/String.js

@@ -29,7 +29,7 @@ function ThrowIncompatibleMethod(name, thisv) {
 // ES 2016 draft Mar 25, 2016 21.1.3.11.
 function String_match(regexp) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("match", this);
   }
 
@@ -37,8 +37,7 @@ function String_match(regexp) {
   var isPatternString = typeof regexp === "string";
   if (
     !(isPatternString && StringProtoHasNoMatch()) &&
-    regexp !== undefined &&
-    regexp !== null
+    !IsNullOrUndefined(regexp)
   ) {
     // Step 2.a.
     var matcher = GetMethod(regexp, GetBuiltinSymbol("match"));
@@ -76,19 +75,19 @@ function String_match(regexp) {
 // String.prototype.matchAll ( regexp )
 function String_matchAll(regexp) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("matchAll", this);
   }
 
   // Step 2.
-  if (regexp !== undefined && regexp !== null) {
+  if (!IsNullOrUndefined(regexp)) {
     // Steps 2.a-b.
     if (IsRegExp(regexp)) {
       // Step 2.b.i.
       var flags = regexp.flags;
 
       // Step 2.b.ii.
-      if (flags === undefined || flags === null) {
+      if (IsNullOrUndefined(flags)) {
         ThrowTypeError(JSMSG_FLAGS_UNDEFINED_OR_NULL);
       }
 
@@ -127,7 +126,7 @@ function String_matchAll(regexp) {
  */
 function String_pad(maxLength, fillString, padEnd) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod(padEnd ? "padEnd" : "padStart", this);
   }
 
@@ -215,15 +214,14 @@ function Substring(str, from, length) {
 // ES 2016 draft Mar 25, 2016 21.1.3.14.
 function String_replace(searchValue, replaceValue) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("replace", this);
   }
 
   // Step 2.
   if (
     !(typeof searchValue === "string" && StringProtoHasNoReplace()) &&
-    searchValue !== undefined &&
-    searchValue !== null
+    !IsNullOrUndefined(searchValue)
   ) {
     // Step 2.a.
     var replacer = GetMethod(searchValue, GetBuiltinSymbol("replace"));
@@ -289,19 +287,19 @@ function String_replace(searchValue, replaceValue) {
 // String.prototype.replaceAll ( searchValue, replaceValue )
 function String_replaceAll(searchValue, replaceValue) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("replaceAll", this);
   }
 
   // Step 2.
-  if (searchValue !== undefined && searchValue !== null) {
+  if (!IsNullOrUndefined(searchValue)) {
     // Steps 2.a-b.
     if (IsRegExp(searchValue)) {
       // Step 2.b.i.
       var flags = searchValue.flags;
 
       // Step 2.b.ii.
-      if (flags === undefined || flags === null) {
+      if (IsNullOrUndefined(flags)) {
         ThrowTypeError(JSMSG_FLAGS_UNDEFINED_OR_NULL);
       }
 
@@ -430,7 +428,7 @@ function IsStringSearchOptimizable() {
 // ES 2016 draft Mar 25, 2016 21.1.3.15.
 function String_search(regexp) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("search", this);
   }
 
@@ -438,8 +436,7 @@ function String_search(regexp) {
   var isPatternString = typeof regexp === "string";
   if (
     !(isPatternString && StringProtoHasNoSearch()) &&
-    regexp !== undefined &&
-    regexp !== null
+    !IsNullOrUndefined(regexp)
   ) {
     // Step 2.a.
     var searcher = GetMethod(regexp, GetBuiltinSymbol("search"));
@@ -483,7 +480,7 @@ function StringProtoHasNoSplit() {
 // ES 2016 draft Mar 25, 2016 21.1.3.17.
 function String_split(separator, limit) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("split", this);
   }
 
@@ -505,8 +502,7 @@ function String_split(separator, limit) {
   // Step 2.
   if (
     !(typeof separator === "string" && StringProtoHasNoSplit()) &&
-    separator !== undefined &&
-    separator !== null
+    !IsNullOrUndefined(separator)
   ) {
     // Step 2.a.
     var splitter = GetMethod(separator, GetBuiltinSymbol("split"));
@@ -559,7 +555,7 @@ function String_split(separator, limit) {
 // 21.1.3.22 String.prototype.substring ( start, end )
 function String_substring(start, end) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("substring", this);
   }
 
@@ -599,7 +595,7 @@ SetIsInlinableLargeFunction(String_substring);
 // B.2.3.1 String.prototype.substr ( start, length )
 function String_substr(start, length) {
   // Steps 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("substr", this);
   }
 
@@ -645,7 +641,7 @@ SetIsInlinableLargeFunction(String_substr);
 // Note: String.prototype.concat.length is 1.
 function String_concat(arg1) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("concat", this);
   }
 
@@ -683,7 +679,7 @@ function String_concat(arg1) {
 // 21.1.3.19 String.prototype.slice ( start, end )
 function String_slice(start, end) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("slice", this);
   }
 
@@ -724,7 +720,7 @@ SetIsInlinableLargeFunction(String_slice);
 // 21.1.3.3 String.prototype.codePointAt ( pos )
 function String_codePointAt(pos) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("codePointAt", this);
   }
 
@@ -762,7 +758,7 @@ function String_codePointAt(pos) {
 // 21.1.3.16 String.prototype.repeat ( count )
 function String_repeat(count) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("repeat", this);
   }
 
@@ -815,7 +811,7 @@ function String_repeat(count) {
 // ES6 draft specification, section 21.1.3.27, version 2013-09-27.
 function String_iterator() {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowTypeError(
       JSMSG_INCOMPATIBLE_PROTO2,
       "String",
@@ -886,7 +882,7 @@ var collatorCache = new_Record();
  */
 function String_localeCompare(that) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("localeCompare", this);
   }
 
@@ -923,7 +919,7 @@ function String_localeCompare(that) {
  */
 function String_toLocaleLowerCase() {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("toLocaleLowerCase", this);
   }
 
@@ -968,7 +964,7 @@ function String_toLocaleLowerCase() {
  */
 function String_toLocaleUpperCase() {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("toLocaleUpperCase", this);
   }
 
@@ -1063,7 +1059,7 @@ function String_static_raw(callSite /*, ...substitutions*/) {
 // String.prototype.at ( index )
 function String_at(index) {
   // Step 1.
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("at", this);
   }
 
@@ -1095,7 +1091,7 @@ function String_at(index) {
 
 // ES6 draft 2014-04-27 B.2.3.3
 function String_big() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("big", this);
   }
   return "<big>" + ToString(this) + "</big>";
@@ -1103,7 +1099,7 @@ function String_big() {
 
 // ES6 draft 2014-04-27 B.2.3.4
 function String_blink() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("blink", this);
   }
   return "<blink>" + ToString(this) + "</blink>";
@@ -1111,7 +1107,7 @@ function String_blink() {
 
 // ES6 draft 2014-04-27 B.2.3.5
 function String_bold() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("bold", this);
   }
   return "<b>" + ToString(this) + "</b>";
@@ -1119,7 +1115,7 @@ function String_bold() {
 
 // ES6 draft 2014-04-27 B.2.3.6
 function String_fixed() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("fixed", this);
   }
   return "<tt>" + ToString(this) + "</tt>";
@@ -1127,7 +1123,7 @@ function String_fixed() {
 
 // ES6 draft 2014-04-27 B.2.3.9
 function String_italics() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("italics", this);
   }
   return "<i>" + ToString(this) + "</i>";
@@ -1135,7 +1131,7 @@ function String_italics() {
 
 // ES6 draft 2014-04-27 B.2.3.11
 function String_small() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("small", this);
   }
   return "<small>" + ToString(this) + "</small>";
@@ -1143,7 +1139,7 @@ function String_small() {
 
 // ES6 draft 2014-04-27 B.2.3.12
 function String_strike() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("strike", this);
   }
   return "<strike>" + ToString(this) + "</strike>";
@@ -1151,7 +1147,7 @@ function String_strike() {
 
 // ES6 draft 2014-04-27 B.2.3.13
 function String_sub() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("sub", this);
   }
   return "<sub>" + ToString(this) + "</sub>";
@@ -1159,7 +1155,7 @@ function String_sub() {
 
 // ES6 draft 2014-04-27 B.2.3.14
 function String_sup() {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("sup", this);
   }
   return "<sup>" + ToString(this) + "</sup>";
@@ -1172,7 +1168,7 @@ function EscapeAttributeValue(v) {
 
 // ES6 draft 2014-04-27 B.2.3.2
 function String_anchor(name) {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("anchor", this);
   }
   var S = ToString(this);
@@ -1181,7 +1177,7 @@ function String_anchor(name) {
 
 // ES6 draft 2014-04-27 B.2.3.7
 function String_fontcolor(color) {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("fontcolor", this);
   }
   var S = ToString(this);
@@ -1190,7 +1186,7 @@ function String_fontcolor(color) {
 
 // ES6 draft 2014-04-27 B.2.3.8
 function String_fontsize(size) {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("fontsize", this);
   }
   var S = ToString(this);
@@ -1199,7 +1195,7 @@ function String_fontsize(size) {
 
 // ES6 draft 2014-04-27 B.2.3.10
 function String_link(url) {
-  if (this === undefined || this === null) {
+  if (IsNullOrUndefined(this)) {
     ThrowIncompatibleMethod("link", this);
   }
   var S = ToString(this);

js/src/builtin/Tuple.js

@@ -273,7 +273,7 @@ function TupleJoin(separator) {
 
   // Steps 3-4
   var sep = ",";
-  if (separator !== undefined && separator !== null) {
+  if (!IsNullOrUndefined(separator)) {
     let toString = IsCallable(separator.toString)
       ? separator.toString
       : std_Object_toString;
@@ -296,7 +296,7 @@ function TupleJoin(separator) {
     let element = T[k];
     // Step 7c
     var next = "";
-    if (element !== undefined && element !== null) {
+    if (!IsNullOrUndefined(element)) {
       let toString = IsCallable(element.toString)
         ? element.toString
         : std_Object_toString;

js/src/builtin/TypedArray.js

@@ -108,7 +108,7 @@ function TypedArraySpeciesConstructor(obj) {
   var s = ctor[GetBuiltinSymbol("species")];
 
   // Step 6.
-  if (s === undefined || s === null) {
+  if (IsNullOrUndefined(s)) {
     return ConstructorForTypedArray(obj);
   }
 

js/src/builtin/Utilities.js

@@ -64,7 +64,7 @@ function GetMethod(V, P) {
   var func = V[P];
 
   // Step 3.
-  if (func === undefined || func === null) {
+  if (IsNullOrUndefined(func)) {
     return undefined;
   }
 
@@ -108,7 +108,7 @@ function SpeciesConstructor(obj, defaultConstructor) {
   var s = ctor[GetBuiltinSymbol("species")];
 
   // Step 6.
-  if (s === undefined || s === null) {
+  if (IsNullOrUndefined(s)) {
     return defaultConstructor;
   }
 
@@ -164,7 +164,7 @@ function CopyDataProperties(target, source, excludedItems) {
   assert(IsObject(excludedItems), "excludedItems is an object");
 
   // Steps 3 and 7.
-  if (source === undefined || source === null) {
+  if (IsNullOrUndefined(source)) {
     return;
   }
 
@@ -205,7 +205,7 @@ function CopyDataPropertiesUnfiltered(target, source) {
   // Step 2 (Not applicable).
 
   // Steps 3 and 7.
-  if (source === undefined || source === null) {
+  if (IsNullOrUndefined(source)) {
     return;
   }
 

js/src/frontend/BytecodeEmitter.cpp

@@ -7403,6 +7403,32 @@ bool BytecodeEmitter::emitSelfHostedToString(CallNode* callNode) {
   return emit1(JSOp::ToString);
 }
 
+bool BytecodeEmitter::emitSelfHostedIsNullOrUndefined(CallNode* callNode) {
+  ListNode* argsList = &callNode->right()->as<ListNode>();
+
+  MOZ_ASSERT(argsList->count() == 1);
+
+  ParseNode* argNode = argsList->head();
+
+  if (!emitTree(argNode)) {
+    //              [stack] ARG
+    return false;
+  }
+  if (!emit1(JSOp::IsNullOrUndefined)) {
+    //              [stack] ARG IS_NULL_OR_UNDEF
+    return false;
+  }
+  if (!emit1(JSOp::Swap)) {
+    //              [stack] IS_NULL_OR_UNDEF ARG
+    return false;
+  }
+  if (!emit1(JSOp::Pop)) {
+    //              [stack] IS_NULL_OR_UNDEF
+    return false;
+  }
+  return true;
+}
+
 bool BytecodeEmitter::emitSelfHostedGetBuiltinConstructorOrPrototype(
     CallNode* callNode, bool isConstructor) {
   ListNode* argsList = &callNode->right()->as<ListNode>();
@@ -8081,6 +8107,9 @@ bool BytecodeEmitter::emitCallOrNew(CallNode* callNode, ValueUsage valueUsage) {
     if (calleeName == TaggedParserAtomIndex::WellKnown::SetCanonicalName()) {
       return emitSelfHostedSetCanonicalName(callNode);
     }
+    if (calleeName == TaggedParserAtomIndex::WellKnown::IsNullOrUndefined()) {
+      return emitSelfHostedIsNullOrUndefined(callNode);
+    }
 #ifdef DEBUG
     if (calleeName ==
             TaggedParserAtomIndex::WellKnown::UnsafeGetReservedSlot() ||

js/src/frontend/BytecodeEmitter.h

@@ -946,6 +946,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
   [[nodiscard]] bool emitSelfHostedHasOwn(CallNode* callNode);
   [[nodiscard]] bool emitSelfHostedToNumeric(CallNode* callNode);
   [[nodiscard]] bool emitSelfHostedToString(CallNode* callNode);
+  [[nodiscard]] bool emitSelfHostedIsNullOrUndefined(CallNode* callNode);
   [[nodiscard]] bool emitSelfHostedGetBuiltinConstructor(CallNode* callNode);
   [[nodiscard]] bool emitSelfHostedGetBuiltinPrototype(CallNode* callNode);
   [[nodiscard]] bool emitSelfHostedGetBuiltinSymbol(CallNode* callNode);

js/src/vm/CommonPropertyNames.h

@@ -295,6 +295,7 @@
   MACRO_(isExtensible, isExtensible, "isExtensible")                           \
   MACRO_(isFinite, isFinite, "isFinite")                                       \
   MACRO_(isNaN, isNaN, "isNaN")                                                \
+  MACRO_(IsNullOrUndefined, IsNullOrUndefined, "IsNullOrUndefined")            \
   MACRO_(isPrototypeOf, isPrototypeOf, "isPrototypeOf")                        \
   MACRO_(isStepStart, isStepStart, "isStepStart")                              \
   MACRO_(isSubsetOf, isSubsetOf, "isSubsetOf")                                 \