[builtins] Support BigInt code stubs for BIG ENDIAN platforms

mjsunit/harmony/bigint/typedarray test failure on mips32 big endian
pointed there was a problem.

Change-Id: I016a31d7758e7bd4019210e23c147dc0f8ea893f
Reviewed-on: https://chromium-review.googlesource.com/995455
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52380}

src/code-stub-assembler.cc

@@ -1730,11 +1730,19 @@ Node* CodeStubAssembler::LoadFixedBigInt64ArrayElementAsTagged(
     TVARIABLE(WordT, var_sign, IntPtrConstant(BigInt::SignBits::encode(false)));
     TVARIABLE(IntPtrT, var_low);
     TVARIABLE(IntPtrT, var_high);
+#if defined(V8_TARGET_BIG_ENDIAN)
+    var_high = UncheckedCast<IntPtrT>(
+        Load(MachineType::UintPtr(), data_pointer, offset));
+    var_low = UncheckedCast<IntPtrT>(
+        Load(MachineType::UintPtr(), data_pointer,
+             Int32Add(offset, Int32Constant(kPointerSize))));
+#else
     var_low = UncheckedCast<IntPtrT>(
         Load(MachineType::UintPtr(), data_pointer, offset));
     var_high = UncheckedCast<IntPtrT>(
         Load(MachineType::UintPtr(), data_pointer,
              Int32Add(offset, Int32Constant(kPointerSize))));
+#endif
 
     Label high_zero(this), negative(this), allocate_one_digit(this),
         allocate_two_digits(this);
@@ -1813,11 +1821,19 @@ Node* CodeStubAssembler::LoadFixedBigUint64ArrayElementAsTagged(
     DCHECK(!Is64());
     Label high_zero(this);
 
+#if defined(V8_TARGET_BIG_ENDIAN)
+    TNode<UintPtrT> high = UncheckedCast<UintPtrT>(
+        Load(MachineType::UintPtr(), data_pointer, offset));
+    TNode<UintPtrT> low = UncheckedCast<UintPtrT>(
+        Load(MachineType::UintPtr(), data_pointer,
+             Int32Add(offset, Int32Constant(kPointerSize))));
+#else
     TNode<UintPtrT> low = UncheckedCast<UintPtrT>(
         Load(MachineType::UintPtr(), data_pointer, offset));
     TNode<UintPtrT> high = UncheckedCast<UintPtrT>(
         Load(MachineType::UintPtr(), data_pointer,
              Int32Add(offset, Int32Constant(kPointerSize))));
+#endif
 
     GotoIf(WordEqual(high, IntPtrConstant(0)), &high_zero);
     var_result = AllocateBigInt(IntPtrConstant(2));
@@ -8234,12 +8250,23 @@ void CodeStubAssembler::EmitBigTypedArrayElementStore(
   Node* offset = ElementOffsetFromIndex(intptr_key, BIGINT64_ELEMENTS,
                                         INTPTR_PARAMETERS, 0);
   MachineRepresentation rep = WordT::kMachineRepresentation;
+#if defined(V8_TARGET_BIG_ENDIAN)
+  if (!Is64()) {
+    StoreNoWriteBarrier(rep, backing_store, offset, var_high.value());
+    StoreNoWriteBarrier(rep, backing_store,
+                        IntPtrAdd(offset, IntPtrConstant(kPointerSize)),
+                        var_low.value());
+  } else {
+    StoreNoWriteBarrier(rep, backing_store, offset, var_low.value());
+  }
+#else
   StoreNoWriteBarrier(rep, backing_store, offset, var_low.value());
   if (!Is64()) {
     StoreNoWriteBarrier(rep, backing_store,
                         IntPtrAdd(offset, IntPtrConstant(kPointerSize)),
                         var_high.value());
   }
+#endif
 }
 
 void CodeStubAssembler::EmitElementStore(Node* object, Node* key, Node* value,