Fix unsafe cast in Value#toString

Change-Id: I6cdcbbee6acc0ff66058d05b6a44f3c004c2c3c3
diff --git a/src/main/java/com/android/tools/r8/ir/code/Value.java b/src/main/java/com/android/tools/r8/ir/code/Value.java
index 6011eb0..f08a4e2 100644
--- a/src/main/java/com/android/tools/r8/ir/code/Value.java
+++ b/src/main/java/com/android/tools/r8/ir/code/Value.java
@@ -801,7 +801,7 @@
                               user.isAnd()
                                   || user.isOr()
                                   || ((user.isShl() || user.isShr() || user.isUshr())
-                                      && constNumberValue == user.asShl().getFirstOperand())
+                                      && constNumberValue == user.getFirstOperand())
                                   || user.isXor());
           if (useBinaryRepresentation) {
             builder.append("0b").append(Integer.toBinaryString(intValue));