[bigint,compiler] Fix endianness issue in bitfield access.

See https://chromium-review.googlesource.com/c/v8/v8/+/904725.

Change-Id: I6b017c0a8d1c521a83e0c6b5315e1c9689bb4f19
Bug: v8:6791
Reviewed-on: https://chromium-review.googlesource.com/906422Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51140}

src/compiler/access-builder.cc

@@ -56,7 +56,7 @@ FieldAccess AccessBuilder::ForHeapNumberValue() {
 FieldAccess AccessBuilder::ForBigIntBitfield() {
   FieldAccess access = {
       kTaggedBase,        BigInt::kBitfieldOffset, MaybeHandle<Name>(),
-      MaybeHandle<Map>(), TypeCache::Get().kInt32, MachineType::Int32(),
+      MaybeHandle<Map>(), TypeCache::Get().kInt32, MachineType::IntPtr(),
       kNoWriteBarrier};
   return access;
 }

src/compiler/effect-control-linearizer.cc

@@ -1175,9 +1175,9 @@ void EffectControlLinearizer::TruncateTaggedPointerToBit(
   __ Bind(&if_bigint);
   {
     Node* bitfield = __ LoadField(AccessBuilder::ForBigIntBitfield(), value);
-    Node* length_is_zero = __ Word32Equal(
-        __ Word32And(bitfield, __ Int32Constant(BigInt::LengthBits::kMask)),
-        zero);
+    Node* length_is_zero = __ WordEqual(
+        __ WordAnd(bitfield, __ IntPtrConstant(BigInt::LengthBits::kMask)),
+        __ IntPtrConstant(0));
     __ Goto(done, __ Word32Equal(length_is_zero, zero));
   }
 }