Add transformation to update loop interation space. Now,

Add transformation to update loop interation space. Now,
for (i=A; i<N; i++) {
  if (i < X && i > Y)
    do_something();
}

is transformed into

U=min(N,X); L=max(A,Y);
for (i=L;i<U;i++)
  do_somethihg();

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42299 91177308-0d34-0410-b5e6-96231b3b80d8