[array] Change fast- to slow-path transition for Array#sort

With the recent changes to Array#sort, the main algorithm does not
need to bail out anymore. Only the initial copying into the workarray,
as well as the final copying back into the original backing store
might cause a switch from fast-path to the slow-path.

This CL changes the slow-path so sorting itself is not restarted and
the slow-path will continue copying where the fast-path left off.

R=jgruber@chromium.org

Bug: v8:7382
Change-Id: I4ab61daa62bb816f4f6e16e60bde1f948ad1e7db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1507717
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60151}

third_party/v8/builtins/array-sort.tq

@@ -14,15 +14,6 @@
 // https://github.com/python/cpython/blob/master/Objects/listsort.txt
 
 namespace array {
-  // All accessors bail to the GenericElementsAccessor if assumptions checked
-  // by "CanUseSameAccessor<>" are violated:
-  //  Generic <- FastPackedSmi
-  //          <- FastSmiOrObject
-  //          <- FastDouble
-  //          <- Dictionary
-  const kGenericElementsAccessorId: Smi = 0;
-  const kFastElementsAccessorId: Smi = 1;
-
   class SortState {
     Compare(implicit context: Context)(x: Object, y: Object): Number {
       const sortCompare: CompareBuiltinFn = this.sortComparePtr;
@@ -40,6 +31,12 @@ namespace array {
       }
     }
 
+    ResetToGenericAccessor() {
+      this.loadFn = Load<GenericElementsAccessor>;
+      this.storeFn = Store<GenericElementsAccessor>;
+      this.bailoutStatus = kSuccess;
+    }
+
     // The receiver of the Array.p.sort call.
     receiver: JSReceiver;
 
@@ -93,10 +90,6 @@ namespace array {
 
     // Pointer to the temporary array.
     tempArray: FixedArray;
-
-    // A Smi constant describing which accessors to use. This is used
-    // for reloading the right elements and for a sanity check.
-    accessor: Smi;
   }
 
   macro NewSortState(implicit context: Context)(
@@ -106,7 +99,6 @@ namespace array {
     const sortComparePtr =
         comparefn != Undefined ? SortCompareUserFn : SortCompareDefault;
     const map = receiver.map;
-    let accessor = kGenericElementsAccessorId;
     let loadFn = Load<GenericElementsAccessor>;
     let storeFn = Store<GenericElementsAccessor>;
     let canUseSameAccessorFn = CanUseSameAccessor<GenericElementsAccessor>;
@@ -117,7 +109,6 @@ namespace array {
         let a: FastJSArray = Cast<FastJSArray>(receiver) otherwise Slow;
 
         const elementsKind: ElementsKind = map.elements_kind;
-        accessor = kFastElementsAccessorId;
         if (IsDoubleElementsKind(elementsKind)) {
           loadFn = Load<FastDoubleElements>;
           storeFn = Store<FastDoubleElements>;
@@ -136,7 +127,6 @@ namespace array {
     label Slow {
       if (map.elements_kind == DICTIONARY_ELEMENTS && IsExtensibleMap(map) &&
           !IsCustomElementsReceiverInstanceType(map.instance_type)) {
-        accessor = kFastElementsAccessorId;
         loadFn = Load<DictionaryElements>;
         storeFn = Store<DictionaryElements>;
         canUseSameAccessorFn = CanUseSameAccessor<DictionaryElements>;
@@ -157,8 +147,7 @@ namespace array {
       0,
       AllocateZeroedFixedArray(Convert<intptr>(kMaxMergePending)),
       AllocateZeroedFixedArray(Convert<intptr>(sortLength)),
-      kEmptyFixedArray,
-      accessor
+      kEmptyFixedArray
     };
   }
 
@@ -1296,55 +1285,59 @@ namespace array {
 
   transitioning macro
   CopyReceiverElementsToWorkArray(
-      implicit context: Context, sortState: SortState)(length: Smi)
-      labels Bailout {
+      implicit context: Context, sortState: SortState)(length: Smi) {
     // TODO(szuend): Investigate if we can use COW arrays or a memcpy + range
     //               barrier to speed this step up.
-    const loadFn = sortState.loadFn;
+    let loadFn = sortState.loadFn;
     const workArray = sortState.workArray;
 
     for (let i: Smi = 0; i < length; ++i) {
+      try {
         workArray.objects[i] = CallLoad(loadFn, i) otherwise Bailout;
       }
+      label Bailout deferred {
+        sortState.ResetToGenericAccessor();
+        loadFn = sortState.loadFn;
+        workArray.objects[i] = CallLoad(loadFn, i) otherwise unreachable;
+      }
+    }
   }
 
   transitioning macro
   CopyWorkArrayToReceiver(implicit context: Context, sortState: SortState)(
-      length: Smi)
-      labels Bailout {
+      length: Smi) {
     // TODO(szuend): Build fast-path that simply installs the work array as the
     // new backing store where applicable.
-    const storeFn = sortState.storeFn;
+    let storeFn = sortState.storeFn;
     const workArray = sortState.workArray;
 
     for (let i: Smi = 0; i < length; ++i) {
+      try {
         CallStore(storeFn, i, workArray.objects[i]) otherwise Bailout;
       }
+      label Bailout deferred {
+        sortState.ResetToGenericAccessor();
+        storeFn = sortState.storeFn;
+        CallStore(storeFn, i, workArray.objects[i]) otherwise unreachable;
+      }
+    }
   }
 
   transitioning builtin
   ArrayTimSort(context: Context, sortState: SortState, length: Smi): Object {
-    try {
-      CopyReceiverElementsToWorkArray(length) otherwise Slow;
+    CopyReceiverElementsToWorkArray(length);
     ArrayTimSortImpl(context, sortState, length);
 
+    try {
       // The comparison function or toString might have changed the
       // receiver, if that is the case, we switch to the slow path.
-      // TODO(szuend): Introduce "special" slow path that only copies,
-      //               but skips the whole re-sorting.
       sortState.CheckAccessor() otherwise Slow;
-      CopyWorkArrayToReceiver(length) otherwise Slow;
-    }
-    label Slow {
-      if (sortState.accessor == kGenericElementsAccessorId) {
-        // We were already on the slow path. This must not happen.
-        unreachable;
     }
-      const newSortState: SortState = NewSortState(
-          sortState.receiver, sortState.userCmpFn,
-          sortState.initialReceiverLength, sortState.workArray.length, true);
-      ArrayTimSort(context, newSortState, length);
+    label Slow deferred {
+      sortState.ResetToGenericAccessor();
     }
+    
+    CopyWorkArrayToReceiver(length);
     return kSuccess;
   }