GetRegForReload() now keeps track which registers have been considered and rejected during its quest to find a suitable reload register. This avoids an infinite loop in case like this:
  t1 := op t2, t3
  t2 <- assigned r0 for use by the reload but ended up reuse r1
  t3 <- assigned r1 for use by the reload but ended up reuse r0
  t1 <- desires r1
        sees r1 is taken by t2, tries t2's reload register r0
        sees r0 is taken by t3, tries t3's reload register r1
        sees r1 is taken by t2, tries t2's reload register r0 ...

llvm-svn: 33382