[change-array-by-copy] Refactor ConvertToRelativeIndex

This refactors ConvertToRelativeIndex into a clamping version and a
version that takes OOB labels for the upcoming implementation of
Array#with and TypedArray#with.

Also gets rid of the the "to" in the name, because these macros are
actually converting _from_ a relative index to an absolute one, not
the other way around.

Bug: v8:12764
Change-Id: I8bf1c16ce73008164acbd6b849f4259fb9315274
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3669655
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80786}

src/builtins/array-at.tq

@@ -3,25 +3,39 @@
 // found in the LICENSE file.
 
 namespace array {
+macro ConvertRelativeIndex(index: Number, length: Number):
+    Number labels OutOfBoundsLow, OutOfBoundsHigh {
+  const relativeIndex = index >= 0 ? index : length + index;
+  if (relativeIndex < 0) goto OutOfBoundsLow;
+  if (relativeIndex >= length) goto OutOfBoundsHigh;
+  return relativeIndex;
+}
+
 // https://tc39.es/proposal-item-method/#sec-array.prototype.at
 transitioning javascript builtin ArrayPrototypeAt(
     js-implicit context: NativeContext, receiver: JSAny)(index: JSAny): JSAny {
   // 1. Let O be ? ToObject(this value).
   const o = ToObject_Inline(context, receiver);
+
   // 2. Let len be ? LengthOfArrayLike(O).
   const len = GetLengthProperty(o);
-  // 3. Let relativeIndex be ? ToInteger(index).
-  const relativeIndex = ToInteger_Inline(index);
-  // 4. If relativeIndex ≥ 0, then
-  //   a. Let k be relativeIndex.
-  // 5. Else,
-  //   a. Let k be len + relativeIndex.
-  const k = relativeIndex >= 0 ? relativeIndex : len + relativeIndex;
-  // 6. If k < 0 or k ≥ len, then return undefined.
-  if (k < 0 || k >= len) {
+
+  try {
+    // 3. Let relativeIndex be ? ToInteger(index).
+    const relativeIndex = ToInteger_Inline(index);
+
+    // 4. If relativeIndex ≥ 0, then
+    //   a. Let k be relativeIndex.
+    // 5. Else,
+    //   a. Let k be len + relativeIndex.
+    const k = ConvertRelativeIndex(relativeIndex, len) otherwise OutOfBounds,
+          OutOfBounds;
+
+    // 7. Return ? Get(O, ! ToString(k)).
+    return GetProperty(o, k);
+  } label OutOfBounds {
+    // 6. If k < 0 or k ≥ len, then return undefined.
     return Undefined;
   }
-  // 7. Return ? Get(O, ! ToString(k)).
-  return GetProperty(o, k);
 }
 }

src/builtins/array-copywithin.tq

@@ -3,8 +3,15 @@
 // found in the LICENSE file.
 
 namespace array {
-macro ConvertToRelativeIndex(index: Number, length: Number): Number {
-  return index < 0 ? Max(index + length, 0) : Min(index, length);
+macro ConvertAndClampRelativeIndex(index: Number, length: Number): Number {
+  try {
+    return ConvertRelativeIndex(index, length) otherwise OutOfBoundsLow,
+           OutOfBoundsHigh;
+  } label OutOfBoundsLow {
+    return 0;
+  } label OutOfBoundsHigh {
+    return length;
+  }
 }
 
 // https://tc39.github.io/ecma262/#sec-array.prototype.copyWithin
@@ -21,14 +28,14 @@ transitioning javascript builtin ArrayPrototypeCopyWithin(
 
   // 4. If relativeTarget < 0, let to be max((len + relativeTarget), 0);
   //    else let to be min(relativeTarget, len).
-  let to: Number = ConvertToRelativeIndex(relativeTarget, length);
+  let to: Number = ConvertAndClampRelativeIndex(relativeTarget, length);
 
   // 5. Let relativeStart be ? ToInteger(start).
   const relativeStart: Number = ToInteger_Inline(arguments[1]);
 
   // 6. If relativeStart < 0, let from be max((len + relativeStart), 0);
   //    else let from be min(relativeStart, len).
-  let from: Number = ConvertToRelativeIndex(relativeStart, length);
+  let from: Number = ConvertAndClampRelativeIndex(relativeStart, length);
 
   // 7. If end is undefined, let relativeEnd be len;
   //    else let relativeEnd be ? ToInteger(end).
@@ -39,7 +46,7 @@ transitioning javascript builtin ArrayPrototypeCopyWithin(
 
   // 8. If relativeEnd < 0, let final be max((len + relativeEnd), 0);
   //    else let final be min(relativeEnd, len).
-  const final: Number = ConvertToRelativeIndex(relativeEnd, length);
+  const final: Number = ConvertAndClampRelativeIndex(relativeEnd, length);
 
   // 9. Let count be min(final-from, len-to).
   let count: Number = Min(final - from, length - to);

src/builtins/base.tq

@@ -1643,44 +1643,65 @@ extern macro IsOneByteStringInstanceType(InstanceType): bool;
 // After converting an index to an integer, calculate a relative index:
 // return index < 0 ? max(length + index, 0) : min(index, length)
 @export
-transitioning macro ConvertToRelativeIndex(implicit context: Context)(
+transitioning macro ConvertAndClampRelativeIndex(implicit context: Context)(
     index: JSAny, length: uintptr): uintptr {
   const indexNumber: Number = ToInteger_Inline(index);
-  return ConvertToRelativeIndex(indexNumber, length);
+  return ConvertAndClampRelativeIndex(indexNumber, length);
 }
 
 // Calculate a relative index:
 // return index < 0 ? max(length + index, 0) : min(index, length)
 @export
-macro ConvertToRelativeIndex(indexNumber: Number, length: uintptr): uintptr {
+macro ConvertAndClampRelativeIndex(indexNumber: Number, length: uintptr):
+    uintptr {
+  try {
+    return ConvertRelativeIndex(indexNumber, length) otherwise OutOfBoundsLow,
+           OutOfBoundsHigh;
+  } label OutOfBoundsLow {
+    return 0;
+  } label OutOfBoundsHigh {
+    return length;
+  }
+}
+
+// Calculate a relative index with explicit out-of-bounds labels.
+macro ConvertRelativeIndex(indexNumber: Number, length: uintptr):
+    uintptr labels OutOfBoundsLow, OutOfBoundsHigh {
   typeswitch (indexNumber) {
     case (indexSmi: Smi): {
       const indexIntPtr: intptr = Convert<intptr>(indexSmi);
       // The logic is implemented using unsigned types.
       if (indexIntPtr < 0) {
         const relativeIndex: uintptr = Unsigned(indexIntPtr) + length;
-        return relativeIndex < length ? relativeIndex : 0;
+        if (relativeIndex < length) return relativeIndex;
+        goto OutOfBoundsLow;
 
       } else {
         const relativeIndex: uintptr = Unsigned(indexIntPtr);
-        return relativeIndex < length ? relativeIndex : length;
+        if (relativeIndex < length) return relativeIndex;
+        goto OutOfBoundsHigh;
       }
     }
     case (indexHeapNumber: HeapNumber): {
       dcheck(IsNumberNormalized(indexHeapNumber));
       const indexDouble: float64 = Convert<float64>(indexHeapNumber);
-      // NaNs must already be handled by ConvertToRelativeIndex() version
+      // NaNs must already be handled by ConvertAndClampRelativeIndex() version
       // above accepting JSAny indices.
       dcheck(!Float64IsNaN(indexDouble));
       const lengthDouble: float64 = Convert<float64>(length);
       dcheck(lengthDouble <= kMaxSafeInteger);
       if (indexDouble < 0) {
         const relativeIndex: float64 = lengthDouble + indexDouble;
-        return relativeIndex > 0 ? ChangeFloat64ToUintPtr(relativeIndex) : 0;
+        if (relativeIndex > 0) {
+          return ChangeFloat64ToUintPtr(relativeIndex);
+        }
+        goto OutOfBoundsLow;
 
       } else {
-        return ChangeFloat64ToUintPtr(
-            indexDouble < lengthDouble ? indexDouble : lengthDouble);
+        if (indexDouble < lengthDouble) {
+          return ChangeFloat64ToUintPtr(indexDouble);
+        }
+        goto OutOfBoundsHigh;
       }
     }
   }

src/builtins/string-slice.tq

@@ -17,13 +17,13 @@ transitioning javascript builtin StringPrototypeSlice(
   // Convert {start} to a relative index.
   const arg0 = arguments[0];
   const start: uintptr =
-      arg0 != Undefined ? ConvertToRelativeIndex(arg0, length) : 0;
+      arg0 != Undefined ? ConvertAndClampRelativeIndex(arg0, length) : 0;
 
   // 5. If end is undefined, let intEnd be len;
   // else Convert {end} to a relative index.
   const arg1 = arguments[1];
   const end: uintptr =
-      arg1 != Undefined ? ConvertToRelativeIndex(arg1, length) : length;
+      arg1 != Undefined ? ConvertAndClampRelativeIndex(arg1, length) : length;
 
   if (end <= start) {
     return kEmptyString;

src/builtins/string-substr.tq

@@ -20,7 +20,7 @@ transitioning javascript builtin StringPrototypeSubstr(
   // 6. If intStart < 0, set intStart to max(size + intStart, 0).
   const start = arguments[0];
   const initStart: uintptr =
-      start != Undefined ? ConvertToRelativeIndex(start, size) : 0;
+      start != Undefined ? ConvertAndClampRelativeIndex(start, size) : 0;
 
   // 4. If length is undefined,
   //   let end be +∞; otherwise let end be ? ToInteger(length).

src/builtins/typed-array-slice.tq

@@ -76,7 +76,7 @@ transitioning javascript builtin TypedArrayPrototypeSlice(
   //    else let k be min(relativeStart, len).
   const start = arguments[0];
   const k: uintptr =
-      start != Undefined ? ConvertToRelativeIndex(start, len) : 0;
+      start != Undefined ? ConvertAndClampRelativeIndex(start, len) : 0;
 
   // 6. If end is undefined, let relativeEnd be len;
   //    else let relativeEnd be ? ToInteger(end).
@@ -84,7 +84,7 @@ transitioning javascript builtin TypedArrayPrototypeSlice(
   //    else let final be min(relativeEnd, len).
   const end = arguments[1];
   let final: uintptr =
-      end != Undefined ? ConvertToRelativeIndex(end, len) : len;
+      end != Undefined ? ConvertAndClampRelativeIndex(end, len) : len;
 
   // 8. Let count be max(final - k, 0).
   let count: uintptr = Unsigned(IntPtrMax(Signed(final - k), 0));

src/builtins/typed-array-subarray.tq

@@ -35,15 +35,16 @@ transitioning javascript builtin TypedArrayPrototypeSubArray(
   // srcLength).
   const arg0 = arguments[0];
   const begin: uintptr =
-      arg0 != Undefined ? ConvertToRelativeIndex(arg0, srcLength) : 0;
+      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).
   const arg1 = arguments[1];
-  const end: uintptr =
-      arg1 != Undefined ? ConvertToRelativeIndex(arg1, srcLength) : srcLength;
+  const end: uintptr = arg1 != Undefined ?
+      ConvertAndClampRelativeIndex(arg1, srcLength) :
+      srcLength;
 
   // 12. Let newLength be max(endIndex - beginIndex, 0).
   const newLength: uintptr = Unsigned(IntPtrMax(Signed(end - begin), 0));

test/cctest/test-code-stub-assembler.cc

@@ -318,7 +318,7 @@ TEST(IsValidPositiveSmi) {
 #endif
 }
 
-TEST(ConvertToRelativeIndex) {
+TEST(ConvertAndClampRelativeIndex) {
   Isolate* isolate(CcTest::InitIsolateOnce());
 
   const int kNumParams = 3;
@@ -335,7 +335,7 @@ TEST(ConvertToRelativeIndex) {
     TNode<UintPtrT> expected =
         m.ChangeUintPtrNumberToUintPtr(expected_relative_index);
 
-    TNode<UintPtrT> result = m.ConvertToRelativeIndex(index, length);
+    TNode<UintPtrT> result = m.ConvertAndClampRelativeIndex(index, length);
 
     m.Return(m.SelectBooleanConstant(m.WordEqual(result, expected)));
   }