Add the last part that is needed for vectorization of if-converted code.

Add the last part that is needed for vectorization of if-converted code.
Added the code that actually performs the if-conversion during vectorization.

We can now vectorize this code:

for (int i=0; i<n; ++i) {
  unsigned k = 0;

  if (a[i] > b[i])   <------ IF inside the loop.
    k = k * 5 + 3;

  a[i] = k;          <---- K is a phi node that becomes vector-select.
}

llvm-svn: 169217