Introduce a flag --limit-ints-to-64-bits in the VM in order to investigate the

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 7482015638326648d80173606445df517d1fcd6b..b9521e685f9797e196d6920253283e7dd1bff946 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -19168,6 +19168,8 @@ RawBigint* Bigint::New(bool neg,
 
 
 RawBigint* Bigint::NewFromInt64(int64_t value, Heap::Space space) {
+  // Currently only used to convert Smi or Mint to hex String, therefore do
+  // not throw RangeError if --limit-ints-to-64-bits.
   const TypedData& digits = TypedData::Handle(NewDigits(2, space));
   bool neg;
   uint64_t abs_value;
@@ -19185,6 +19187,10 @@ RawBigint* Bigint::NewFromInt64(int64_t value, Heap::Space space) {
 
 
 RawBigint* Bigint::NewFromUint64(uint64_t value, Heap::Space space) {
+  if (FLAG_limit_ints_to_64_bits) {
+    Exceptions::ThrowRangeErrorMsg(
+        "Integer operand requires conversion to Bigint");
+  }
   const TypedData& digits = TypedData::Handle(NewDigits(2, space));
   SetDigitAt(digits, 0, static_cast<uint32_t>(value));
   SetDigitAt(digits, 1, static_cast<uint32_t>(value >> 32));
@@ -19195,6 +19201,12 @@ RawBigint* Bigint::NewFromUint64(uint64_t value, Heap::Space space) {
 RawBigint* Bigint::NewFromShiftedInt64(int64_t value,
                                        intptr_t shift,
                                        Heap::Space space) {
+  if (FLAG_limit_ints_to_64_bits) {
+    // The allocated Bigint value is not necessarily out of range, but it may
+    // be used as an operand in an operation resulting in a Bigint.
+    Exceptions::ThrowRangeErrorMsg(
+        "Integer operand requires conversion to Bigint");
+  }
   ASSERT(kBitsPerDigit == 32);
   ASSERT(shift >= 0);
   const intptr_t digit_shift = shift / kBitsPerDigit;
@@ -19225,6 +19237,7 @@ RawBigint* Bigint::NewFromShiftedInt64(int64_t value,
 
 
 RawBigint* Bigint::NewFromCString(const char* str, Heap::Space space) {
+  // Allow parser to scan Bigint literal, even with --limit-ints-to-64-bits.
   ASSERT(str != NULL);
   bool neg = false;
   TypedData& digits = TypedData::Handle();
@@ -19246,6 +19259,7 @@ RawBigint* Bigint::NewFromCString(const char* str, Heap::Space space) {
 
 
 RawBigint* Bigint::NewCanonical(const String& str) {
+  // Allow parser to scan Bigint literal, even with --limit-ints-to-64-bits.
   Thread* thread = Thread::Current();
   Zone* zone = thread->zone();
   Isolate* isolate = thread->isolate();