Add reference to problem report.

llvm-svn: 40889
diff --git a/llvm/test/Analysis/ScalarEvolution/2007-08-06-Unsigned.ll b/llvm/test/Analysis/ScalarEvolution/2007-08-06-Unsigned.ll
index 1b8dc4d..3051472 100644
--- a/llvm/test/Analysis/ScalarEvolution/2007-08-06-Unsigned.ll
+++ b/llvm/test/Analysis/ScalarEvolution/2007-08-06-Unsigned.ll
@@ -1,4 +1,5 @@
 ; RUN: llvm-as < %s | opt -scalar-evolution -analyze |& grep "Loop bb: ( -1 + ( -1 *  %x) +  %y) iterations!"
+; PR1597
 
 define i32 @f(i32 %x, i32 %y) {
 entry: