noduplicate prevents unrolling of small loops that happen to have
barriers in them. If a loop has a barrier in it, it is OK to duplicate
it for the unroll.
llvm-svn: 256075
sub C, x - > add (sub 0, x), C for DS offsets.
This is mostly to fix regressions that show up when
SeparateConstOffsetFromGEP is enabled.
llvm-svn: 247054