Explicitly initialize Bigint members after uninitialized allocations.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index f4e69460b8f55acdf07f10c463f9d6a803823309..316df393de91ab0a4709c17cf9a2eaddeb2aa921 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -249,10 +249,12 @@ RawBigint* SnapshotReader::NewBigint(const char* hex_string) {
   ASSERT(isolate()->no_gc_scope_depth() != 0);
   cls_ = object_store()->bigint_class();
   intptr_t bigint_length = BigintOperations::ComputeChunkLength(hex_string);
-  const Bigint& result = Bigint::Handle(reinterpret_cast<RawBigint*>(
-      AllocateUninitialized(cls_, Bigint::InstanceSize(bigint_length))));
-  BigintOperations::FromHexCString(hex_string, result);
-  return result.raw();
+  RawBigint* obj = reinterpret_cast<RawBigint*>(
+      AllocateUninitialized(cls_, Bigint::InstanceSize(bigint_length)));
+  obj->ptr()->allocated_length_ = bigint_length;
+  obj->ptr()->signed_length_ = bigint_length;

[siva, 2012/04/26 04:45:04]

why not add a set_allocated_length() and set_signed_length() in object.h and use
them here

or

Bigint& result = Bigint::Handle();
{
  NoGCScope nogc;
  result = AllocateUninitialized(...);
  result.raw()->ptr()->allocated_length_ = ...
  result.raw()->ptr()->signed_length_ = ...
 }
 BigintOperations::FromHexCString(...);
 return

[cshapiro, 2012/04/26 06:34:53]

Hmm... I tried to make the code look like the rest of the code in the snapshot
reader.

The NoGCScope seemed unnecessary because of the assert on line 249 and because
the entire read is wrapped in a NoGCScope on line 130.

We have a SetLength but it does something different than one would expect.  It
is confusing to me why we have these two length values in the first place.  
Let's talk about this off-line.

[siva, 2012/04/26 17:17:44]

Agree, I didn't realize we already had a NoGCScope around the caller.

Maybe in a different CL, I will add an assertion in each of this functions so
that there is no confusion.

On 2012/04/26 06:34:53, cshapiro wrote:

+  BigintOperations::FromHexCString(hex_string, Bigint::Handle(obj));
+  return obj;
 }