Add handling for hashed uninflated object.

This is an Optimization to reduce how often we call
System.identityHashCode. If the lockword is set to the hash code
state then we simply return this value. Otherwise, we use
System.identityHashCode.

Maps launch exclusive time spent in System.identityHashCode:
Before: 4.5%
After: 2.4%

Bug: 16828525

(cherry picked from commit 6917aebf2eb26c2b003a72d09c1c5bb6310160b0)

Change-Id: I0ccad53cb5f8f4f27fe11725a91ab45a117452a3

1 files changed, 6 insertions, 0 deletions

diff --git a/libart/src/main/java/java/lang/Object.java b/libart/src/main/java/java/lang/Object.java
index acae8ca..20fdbf9 100644
--- a/libart/src/main/java/java/lang/Object.java
+++ b/libart/src/main/java/java/lang/Object.java
@@ -273,6 +273,12 @@ public class Object {
      * @see #equals
      */
     public int hashCode() {
+        int lockWord = shadow$_monitor_;
+        final int lockWordMask = 0xC0000000;  // Top 2 bits.
+        final int lockWordStateHash = 0x80000000;  // Top 2 bits are value 2 (kStateHash).
+        if ((lockWord & lockWordMask) == lockWordStateHash) {
+            return lockWord & ~lockWordMask;
+        }
         return System.identityHashCode(this);
     }