Lazily compute object identity hash codes.

Before, we computed identity hashcodes whenever we inflated a monitor.
This caused issues since it meant that we would have all of these
hash codes in the image, causing locks to excessively inflate during
application run time.

This change makes it so that we lazily compute hash codes. When a
thin lock gets inflated, we assign a hash code of 0 assigned to it.
This value signifies no hash code. When we try to get the identity
hash code of an object with an inflated monitor, it gets computed if
it is 0.

Change-Id: Iae6acd1960515a36e74644e5b1323ff336731806

1 files changed, 7 insertions, 2 deletions

diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index af60a38..75be2c9 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -504,7 +504,11 @@ void ImageWriter::CopyAndFixupObjectsCallback(Object* object, void* arg) {
       Monitor* monitor = lw.FatLockMonitor();
       CHECK(monitor != nullptr);
       CHECK(!monitor->IsLocked());
-      copy->SetLockWord(LockWord::FromHashCode(monitor->GetHashCode()));
+      if (monitor->HasHashCode()) {
+        copy->SetLockWord(LockWord::FromHashCode(monitor->GetHashCode()));
+      } else {
+        copy->SetLockWord(LockWord());
+      }
       break;
     }
     case LockWord::kThinLocked: {
@@ -512,9 +516,10 @@ void ImageWriter::CopyAndFixupObjectsCallback(Object* object, void* arg) {
       break;
     }
     case LockWord::kUnlocked:
-      // Fall-through.
+      break;
     case LockWord::kHashCode:
       // Do nothing since we can just keep the same hash code.
+      CHECK_NE(lw.GetHashCode(), 0);
       break;
     default:
       LOG(FATAL) << "Unreachable.";