Bug 1847714 part 3 - Tidy up match result code more. r=iain

* Use `initSlot` instead of `setSlot` because it's a little faster.
* Use default `undefined` value for template object slots.
* Remove some unnecessary stores in match stub code.
* Use named constants instead of 0 and 1 in `BuildFlatMatchArray`.
* The template array object can be an empty array now.

Differential Revision: https://phabricator.services.mozilla.com/D185652

js/src/builtin/RegExp.cpp

@@ -154,10 +154,8 @@ bool js::CreateRegExpMatchResult(JSContext* cx, HandleRegExpShared re,
       if (!indicesGroups) {
         return false;
       }
-      indices->setSlot(RegExpRealm::IndicesGroupsSlot,
-                       ObjectValue(*indicesGroups));
-    } else {
-      indices->setSlot(RegExpRealm::IndicesGroupsSlot, UndefinedValue());
+      indices->initSlot(RegExpRealm::IndicesGroupsSlot,
+                        ObjectValue(*indicesGroups));
     }
 
     // MakeIndicesArray: step 13 a-d. (Step 13.e is implemented below.)
@@ -231,34 +229,36 @@ bool js::CreateRegExpMatchResult(JSContext* cx, HandleRegExpShared re,
   } else {
     for (uint32_t i = 0; i < re->numNamedCaptures(); i++) {
       uint32_t idx = re->getNamedCaptureIndex(i);
-      groups->setSlot(i, arr->getDenseElement(idx));
+      groups->initSlot(i, arr->getDenseElement(idx));
 
       // MakeIndicesArray: Step 13.e (reordered)
       if (hasIndices) {
-        indicesGroups->setSlot(i, indices->getDenseElement(idx));
+        indicesGroups->initSlot(i, indices->getDenseElement(idx));
       }
     }
   }
 
   // Step 22 (reordered).
   // Set the |index| property.
-  arr->setSlot(RegExpRealm::MatchResultObjectIndexSlot,
-               Int32Value(matches[0].start));
+  arr->initSlot(RegExpRealm::MatchResultObjectIndexSlot,
+                Int32Value(matches[0].start));
 
   // Step 23 (reordered).
   // Set the |input| property.
-  arr->setSlot(RegExpRealm::MatchResultObjectInputSlot, StringValue(input));
+  arr->initSlot(RegExpRealm::MatchResultObjectInputSlot, StringValue(input));
 
   // Step 32 (reordered)
   // Set the |groups| property.
-  arr->setSlot(RegExpRealm::MatchResultObjectGroupsSlot,
-               groups ? ObjectValue(*groups) : UndefinedValue());
+  if (groups) {
+    arr->initSlot(RegExpRealm::MatchResultObjectGroupsSlot,
+                  ObjectValue(*groups));
+  }
 
   // Step 34b
   // Set the |indices| property.
   if (re->hasIndices()) {
-    arr->setSlot(RegExpRealm::MatchResultObjectIndicesSlot,
-                 ObjectValue(*indices));
+    arr->initSlot(RegExpRealm::MatchResultObjectIndicesSlot,
+                  ObjectValue(*indices));
   }
 
 #ifdef DEBUG

js/src/builtin/String.cpp

@@ -4538,11 +4538,11 @@ static bool BuildFlatMatchArray(JSContext* cx, HandleString str,
   arr->setDenseInitializedLength(1);
   arr->initDenseElement(0, StringValue(pattern));
 
-  // Set the |index| property. (TemplateObject positions it in slot 0).
-  arr->setSlot(0, Int32Value(match));
+  // Set the |index| property.
+  arr->initSlot(RegExpRealm::MatchResultObjectIndexSlot, Int32Value(match));
 
-  // Set the |input| property. (TemplateObject positions it in slot 1).
-  arr->setSlot(1, StringValue(str));
+  // Set the |input| property.
+  arr->initSlot(RegExpRealm::MatchResultObjectInputSlot, StringValue(str));
 
 #ifdef DEBUG
   RootedValue test(cx);

js/src/jit/CodeGenerator.cpp

@@ -2552,26 +2552,6 @@ static JitCode* GenerateRegExpMatchStubShared(JSContext* cx,
     masm.bind(&allocated);
   }
 
-  static_assert(RegExpRealm::MatchResultObjectIndexSlot == 0,
-                "First slot holds the 'index' property");
-  static_assert(RegExpRealm::MatchResultObjectInputSlot == 1,
-                "Second slot holds the 'input' property");
-  static_assert(RegExpRealm::MatchResultObjectGroupsSlot == 2,
-                "Third slot holds the 'groups' property");
-
-  // Initialize the slots of the result object with the dummy values
-  // defined in createMatchResultTemplateObject.
-  masm.loadPtr(Address(object, NativeObject::offsetOfSlots()), temp2);
-  masm.storeValue(
-      nativeTemplateObj.getSlot(RegExpRealm::MatchResultObjectIndexSlot),
-      Address(temp2, RegExpRealm::offsetOfMatchResultObjectIndexSlot()));
-  masm.storeValue(
-      nativeTemplateObj.getSlot(RegExpRealm::MatchResultObjectInputSlot),
-      Address(temp2, RegExpRealm::offsetOfMatchResultObjectInputSlot()));
-  masm.storeValue(
-      nativeTemplateObj.getSlot(RegExpRealm::MatchResultObjectGroupsSlot),
-      Address(temp2, RegExpRealm::offsetOfMatchResultObjectGroupsSlot()));
-
   // clang-format off
    /*
     * [SMDOC] Stack layout for the RegExpMatcher stub
@@ -2731,6 +2711,11 @@ static JitCode* GenerateRegExpMatchStubShared(JSContext* cx,
   Address firstMatchPairLimitAddress(
       FramePointer, pairsVectorStartOffset + MatchPair::offsetOfLimit());
 
+  static_assert(RegExpRealm::MatchResultObjectIndexSlot == 0,
+                "First slot holds the 'index' property");
+  static_assert(RegExpRealm::MatchResultObjectInputSlot == 1,
+                "Second slot holds the 'input' property");
+
   masm.loadPtr(Address(object, NativeObject::offsetOfSlots()), temp2);
 
   masm.load32(firstMatchPairStartAddress, temp3);

js/src/vm/RegExpObject.cpp

@@ -863,18 +863,15 @@ ArrayObject* RegExpRealm::createMatchResultTemplateObject(
   MOZ_ASSERT(!matchResultTemplateObjects_[kind]);
 
   /* Create template array object */
-  Rooted<ArrayObject*> templateObject(
-      cx,
-      NewDenseUnallocatedArray(cx, RegExpObject::MaxPairCount, TenuredObject));
+  Rooted<ArrayObject*> templateObject(cx, NewTenuredDenseEmptyArray(cx));
   if (!templateObject) {
     return nullptr;
   }
 
   if (kind == ResultTemplateKind::Indices) {
     /* The |indices| array only has a |groups| property. */
-    RootedValue groupsVal(cx, UndefinedValue());
     if (!NativeDefineDataProperty(cx, templateObject, cx->names().groups,
-                                  groupsVal, JSPROP_ENUMERATE)) {
+                                  UndefinedHandleValue, JSPROP_ENUMERATE)) {
       return nullptr;
     }
     MOZ_ASSERT(templateObject->getLastProperty().slot() == IndicesGroupsSlot);
@@ -884,27 +881,24 @@ ArrayObject* RegExpRealm::createMatchResultTemplateObject(
   }
 
   /* Set dummy index property */
-  RootedValue index(cx, Int32Value(0));
-  if (!NativeDefineDataProperty(cx, templateObject, cx->names().index, index,
-                                JSPROP_ENUMERATE)) {
+  if (!NativeDefineDataProperty(cx, templateObject, cx->names().index,
+                                UndefinedHandleValue, JSPROP_ENUMERATE)) {
     return nullptr;
   }
   MOZ_ASSERT(templateObject->getLastProperty().slot() ==
              MatchResultObjectIndexSlot);
 
   /* Set dummy input property */
-  RootedValue inputVal(cx, StringValue(cx->runtime()->emptyString));
-  if (!NativeDefineDataProperty(cx, templateObject, cx->names().input, inputVal,
-                                JSPROP_ENUMERATE)) {
+  if (!NativeDefineDataProperty(cx, templateObject, cx->names().input,
+                                UndefinedHandleValue, JSPROP_ENUMERATE)) {
     return nullptr;
   }
   MOZ_ASSERT(templateObject->getLastProperty().slot() ==
              MatchResultObjectInputSlot);
 
   /* Set dummy groups property */
-  RootedValue groupsVal(cx, UndefinedValue());
   if (!NativeDefineDataProperty(cx, templateObject, cx->names().groups,
-                                groupsVal, JSPROP_ENUMERATE)) {
+                                UndefinedHandleValue, JSPROP_ENUMERATE)) {
     return nullptr;
   }
   MOZ_ASSERT(templateObject->getLastProperty().slot() ==
@@ -912,9 +906,8 @@ ArrayObject* RegExpRealm::createMatchResultTemplateObject(
 
   if (kind == ResultTemplateKind::WithIndices) {
     /* Set dummy indices property */
-    RootedValue indicesVal(cx, UndefinedValue());
     if (!NativeDefineDataProperty(cx, templateObject, cx->names().indices,
-                                  indicesVal, JSPROP_ENUMERATE)) {
+                                  UndefinedHandleValue, JSPROP_ENUMERATE)) {
       return nullptr;
     }
     MOZ_ASSERT(templateObject->getLastProperty().slot() ==