Only allow instance-of to improve knowledge of a type for downcasts.

Previous "not upcast" test could improve a type to an impossible type that
following a merge back with the original register would lead to conflict
(and subsequent verifier errors).
Modify UpdateRegisters so that the work line will be updated if merging
causes changes in the fall-through case.

Bug: 15808277
Issue: https://code.google.com/p/android/issues/detail?id=72093
Change-Id: Ib16cae8506246177e902825af036d5a397ad0dac

1 files changed, 12 insertions, 0 deletions

diff --git a/test/052-verifier-fun/src/Main.java b/test/052-verifier-fun/src/Main.java
index 0168412..3ffd143 100644
--- a/test/052-verifier-fun/src/Main.java
+++ b/test/052-verifier-fun/src/Main.java
@@ -24,6 +24,7 @@ public class Main {
         tryBlah(1);
 
         System.out.println("Zorch.");
+        System.out.println("10 == " + instanceOfTest(10));
     }
 
     /*
@@ -120,4 +121,15 @@ public class Main {
 
         feature.doStuff();
     }
+
+    static int instanceOfTest(Integer x) {
+      Object y = x;
+      if (y instanceof String) {
+        // Bug: 15808277
+        // Non-sensical instance-of to check merging after the branch doesn't result in a verifier
+        // error.
+        ((String)y).charAt(0);
+      }
+      return x.intValue();
+    }
 }