[rab/gsab] Fix length-tracking handling in TA#subarray

The normative change in
https://github.com/tc39/proposal-resizablearraybuffer/pull/93 changed
the behavior of TypedArray.prototype.subarray(begin, end) such that if
the receiver is a length-tracking TA and end is undefined, the result
TypedArray is also length-tracking.

This change reached consensus in the March 2022 TC39.

Bug: v8:11111
Change-Id: If1a84cc3134f3ce8046196d6cc36683b6996dec0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3888382
Commit-Queue: Marja Hölttä <marja@chromium.org>
Auto-Submit: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83147}

src/builtins/typed-array-createtypedarray.tq

@@ -478,12 +478,12 @@ transitioning macro TypedArraySpeciesCreateByLength(implicit context: Context)(
 
 transitioning macro TypedArraySpeciesCreateByBuffer(implicit context: Context)(
     methodName: constexpr string, exemplar: JSTypedArray, buffer: JSArrayBuffer,
-    beginByteOffset: uintptr, newLength: uintptr): JSTypedArray {
+    beginByteOffset: uintptr, newLength: NumberOrUndefined): JSTypedArray {
   const numArgs: constexpr int31 = 3;
   // TODO(v8:4153): pass length further as uintptr.
   const typedArray: JSTypedArray = TypedArraySpeciesCreate(
       methodName, numArgs, exemplar, buffer, Convert<Number>(beginByteOffset),
-      Convert<Number>(newLength));
+      newLength);
   return typedArray;
 }
 

src/builtins/typed-array-subarray.tq

@@ -10,16 +10,18 @@ transitioning javascript builtin TypedArrayPrototypeSubArray(
   const methodName: constexpr string = '%TypedArray%.prototype.subarray';
 
   // 1. Let O be the this value.
-  // 3. If O does not have a [[TypedArrayName]] internal slot, throw a
-  // TypeError exception.
+  // 2. Perform ? RequireInternalSlot(O, [[TypedArrayName]]).
   const source = Cast<JSTypedArray>(receiver)
       otherwise ThrowTypeError(
       MessageTemplate::kIncompatibleMethodReceiver, methodName);
 
-  // 5. Let buffer be O.[[ViewedArrayBuffer]].
+  // 3. Assert: O has a [[ViewedArrayBuffer]] internal slot.
+  // 4. Let buffer be O.[[ViewedArrayBuffer]].
   const buffer = typed_array::GetTypedArrayBuffer(source);
 
-  // 6. Let srcLength be O.[[ArrayLength]].
+  // 5. Let getSrcBufferByteLength be
+  //    MakeIdempotentArrayBufferByteLengthGetter(SeqCst).
+  // 6. Let srcLength be IntegerIndexedObjectLength(O, getSrcBufferByteLength).
   let srcLength: uintptr;
   try {
     srcLength = LoadJSTypedArrayLengthAndCheckDetached(source)
@@ -29,41 +31,57 @@ transitioning javascript builtin TypedArrayPrototypeSubArray(
     srcLength = 0;
   }
 
-  // 8. Let relativeBegin be ? ToInteger(begin).
-  // 9. If relativeBegin < 0, let beginIndex be max((srcLength +
-  // relativeBegin), 0); else let beginIndex be min(relativeBegin,
-  // srcLength).
+  // 8. Let relativeBegin be ? ToIntegerOrInfinity(begin).
+  // 9. If relativeBegin is -∞, let beginIndex be 0.
+  // 10. Else if relativeBegin < 0, let beginIndex be max(srcLength +
+  //     relativeBegin, 0).
+  // 11. Else, let beginIndex be min(relativeBegin, srcLength).
   const arg0 = arguments[0];
   const begin: uintptr =
       arg0 != Undefined ? ConvertAndClampRelativeIndex(arg0, srcLength) : 0;
 
-  // 10. If end is undefined, let relativeEnd be srcLength;
-  //      else, let relativeEnd be ? ToInteger(end).
-  // 11. If relativeEnd < 0, let endIndex be max((srcLength + relativeEnd),
-  // 0); else let endIndex be min(relativeEnd, srcLength).
+  // 12. If O.[[ArrayLength]] is auto and end is undefined, then
   const arg1 = arguments[1];
-  const end: uintptr = arg1 != Undefined ?
+  const endIsDefined = arg1 != Undefined;
+
+  let newLength: NumberOrUndefined;
+  if (IsLengthTrackingJSArrayBufferView(source) && !endIsDefined) {
+    // a. Let newLength be undefined.
+    newLength = Undefined;
+  } else {
+    // 13. Else,
+    //   a. If end is undefined, let relativeEnd be srcLength; else let
+    //      relativeEnd be ? ToIntegerOrInfinity(end).
+    //   b. If relativeEnd is -∞, let endIndex be 0.
+    //   c. Else if relativeEnd < 0, let endIndex be max(srcLength +
+    //      relativeEnd, 0).
+    //   d. Else, let endIndex be min(relativeEnd, srcLength).
+    const end: uintptr = endIsDefined ?
         ConvertAndClampRelativeIndex(arg1, srcLength) :
         srcLength;
 
-  // 12. Let newLength be max(endIndex - beginIndex, 0).
-  const newLength: uintptr = Unsigned(IntPtrMax(Signed(end - begin), 0));
+    //   e. Let newLength be max(endIndex - beginIndex, 0).
+    newLength = Convert<Number>(Unsigned(IntPtrMax(Signed(end - begin), 0)));
+  }
 
-  // 13. Let constructorName be the String value of O.[[TypedArrayName]].
-  // 14. Let elementSize be the Number value of the Element Size value
+  // 14. Let constructorName be the String value of O.[[TypedArrayName]].
+  // 15. Let elementSize be the Number value of the Element Size value
   // specified in Table 52 for constructorName.
   const elementsInfo = typed_array::GetTypedArrayElementsInfo(source);
 
-  // 15. Let srcByteOffset be O.[[ByteOffset]].
+  // 16. Let srcByteOffset be O.[[ByteOffset]].
   const srcByteOffset: uintptr = source.byte_offset;
 
-  // 16. Let beginByteOffset be srcByteOffset + beginIndex × elementSize.
+  // 17. Let beginByteOffset be srcByteOffset + beginIndex × elementSize.
   const beginByteOffset =
       srcByteOffset + elementsInfo.CalculateByteLength(begin)
       otherwise ThrowRangeError(MessageTemplate::kInvalidArrayBufferLength);
 
-  // 17. Let argumentsList be « buffer, beginByteOffset, newLength ».
-  // 18. Return ? TypedArraySpeciesCreate(O, argumentsList).
+  // 18. If newLength is undefined, then
+  //   a. Let argumentsList be « buffer, 𝔽(beginByteOffset) ».
+  // 19. Else,
+  //   a. Let argumentsList be « buffer, 𝔽(beginByteOffset), 𝔽(newLength) ».
+  // 20. Return ? TypedArraySpeciesCreate(O, argumentsList).
   return TypedArraySpeciesCreateByBuffer(
       methodName, source, buffer, beginByteOffset, newLength);
 }

test/mjsunit/typedarray-growablesharedarraybuffer.js

@@ -3437,11 +3437,11 @@ Reverse(ArrayReverseHelper);
     assertEquals(4, fixedLengthSubFull.length);
     assertEquals(2, fixedLengthWithOffsetSubFull.length);
 
-    // TODO(v8:11111): Are subarrays of length-tracking TAs also
-    // length-tracking? See
-    // https://github.com/tc39/proposal-resizablearraybuffer/issues/91
-    assertEquals(4, lengthTrackingSubFull.length);
-    assertEquals(2, lengthTrackingWithOffsetSubFull.length);
+    // Subarrays of length-tracking TAs that don't pass an explicit end argument
+    // are also length-tracking.
+    assertEquals(lengthTracking.length, lengthTrackingSubFull.length);
+    assertEquals(lengthTrackingWithOffset.length,
+                 lengthTrackingWithOffsetSubFull.length);
   }
 })();
 
@@ -3479,7 +3479,8 @@ Reverse(ArrayReverseHelper);
     const evil = { valueOf: () => { gsab.grow(6 * ctor.BYTES_PER_ELEMENT);
                                     return 0;}};
 
-    assertEquals([0, 2, 4, 6], ToNumbers(lengthTracking.subarray(evil)));
+    assertEquals([0, 2, 4, 6], ToNumbers(
+      lengthTracking.subarray(evil, lengthTracking.length)));
   }
 })();
 

test/mjsunit/typedarray-resizablearraybuffer.js

@@ -6682,11 +6682,11 @@ Reverse(ArrayReverseHelper, false);
     assertEquals(4, fixedLengthSubFull.length);
     assertEquals(2, fixedLengthWithOffsetSubFull.length);
 
-    // TODO(v8:11111): Are subarrays of length-tracking TAs also
-    // length-tracking? See
-    // https://github.com/tc39/proposal-resizablearraybuffer/issues/91
-    assertEquals(4, lengthTrackingSubFull.length);
-    assertEquals(2, lengthTrackingWithOffsetSubFull.length);
+    // Subarrays of length-tracking TAs that don't pass an explicit end argument
+    // are also length-tracking.
+    assertEquals(lengthTracking.length, lengthTrackingSubFull.length);
+    assertEquals(lengthTrackingWithOffset.length,
+                 lengthTrackingWithOffsetSubFull.length);
   }
 })();
 
@@ -6779,7 +6779,9 @@ Reverse(ArrayReverseHelper, false);
       rab.resize(2 * ctor.BYTES_PER_ELEMENT);
       return 0;
     }};
-    assertThrows(() => { lengthTracking.subarray(evil); });
+    assertThrows(() => {
+      lengthTracking.subarray(evil, lengthTracking.length);
+    });
   }
 
   // Like the previous test, but now we construct a smaller subarray and it
@@ -6874,7 +6876,8 @@ Reverse(ArrayReverseHelper, false);
     const evil = { valueOf: () => { rab.resize(6 * ctor.BYTES_PER_ELEMENT);
                                     return 0;}};
 
-    assertEquals([0, 2, 4, 6], ToNumbers(lengthTracking.subarray(evil)));
+    assertEquals([0, 2, 4, 6], ToNumbers(
+      lengthTracking.subarray(evil, lengthTracking.length)));
   }
 })();