Changed the likelihood.

Changed the likelihoood of the mutation and added documentation to the
mutation.

Test: Performed. Ran dexfuzz and waited until mutation kicked in.
Change-Id: I878c1c3434cf17ae8eb1172bf0c326bf15629d5e
diff --git a/tools/dexfuzz/README b/tools/dexfuzz/README
index a635fe9..1f74262 100644
--- a/tools/dexfuzz/README
+++ b/tools/dexfuzz/README
@@ -145,7 +145,7 @@
 PoolIndexChanger 30
 RandomBranchChanger 30
 RandomInstructionGenerator 30
-RegisterClobber 40
+RegisterClobber 10
 SwitchBranchShifter 30
 TryBlockShifter 40
 ValuePrinter 40
diff --git a/tools/dexfuzz/src/dexfuzz/DexFuzz.java b/tools/dexfuzz/src/dexfuzz/DexFuzz.java
index b0ce5a8..2b3b8e7 100644
--- a/tools/dexfuzz/src/dexfuzz/DexFuzz.java
+++ b/tools/dexfuzz/src/dexfuzz/DexFuzz.java
@@ -33,9 +33,9 @@
  * Entrypoint class for dexfuzz.
  */
 public class DexFuzz {
-  // Last version update 1.6: added temporary register to ArrayLengthChanger.
+  // Last version update 1.7: changed the likelihood of RegisterClobber.
   private static int majorVersion = 1;
-  private static int minorVersion = 6;
+  private static int minorVersion = 7;
   private static int seedChangeVersion = 0;
 
   /**
diff --git a/tools/dexfuzz/src/dexfuzz/program/mutators/RegisterClobber.java b/tools/dexfuzz/src/dexfuzz/program/mutators/RegisterClobber.java
index 11da1d4..90f4f0f 100644
--- a/tools/dexfuzz/src/dexfuzz/program/mutators/RegisterClobber.java
+++ b/tools/dexfuzz/src/dexfuzz/program/mutators/RegisterClobber.java
@@ -61,7 +61,7 @@
 
   public RegisterClobber(Random rng, MutationStats stats, List<Mutation> mutations) {
     super(rng, stats, mutations);
-    likelihood = 40;
+    likelihood = 10;
   }
 
   @Override
@@ -90,6 +90,7 @@
       newInsn.insn = new Instruction();
       newInsn.insn.info = Instruction.getOpcodeInfo(Opcode.CONST_16);
       newInsn.insn.vregA = i;
+      // Used zero because it may also apply to objects, resulting in fewer verification failures.
       newInsn.insn.vregB = 0;
       mutatableCode.insertInstructionAt(newInsn, mutation.regClobberIdx + i);
     }