GVN: Fix quadratic runtime on the number of switch cases.

No intended behavior change.  This was introduced in r162023.  With the fixed
algorithm a Release build of ARMInstPrinter.cpp goes from 16s to 10s on a
2011 MBP.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162559 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed