v2: tighten the sub64 tests
v3: rename to CARRY/BORROW
v4: fixup test cmdline
add known bits computation
use sign extend instead of sub 0,x
better add test
v5: remove redundant break
move lowering to separate functions
fix comments
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewers: arsenm
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234759 91177308-0d34-0410-b5e6-96231b3b80d8