[Thumb] Reapply r272251 with a fix for PR28348 (mk 2)

The important thing I was missing was ensuring newly added constants were kept in topological order. Repositioning the node is correct if the constant is newly added (so it has no topological ordering) but wrong if it already existed - positioning it next in the worklist would break the topological ordering.

Original commit message:
  [Thumb] Select a BIC instead of AND if the immediate can be encoded more optimally negated

  If an immediate is only used in an AND node, it is possible that the immediate can be more optimally materialized when negated. If this is the case, we can negate the immediate and use a BIC instead;

    int i(int a) {
      return a & 0xfffffeec;
    }

  Used to produce:
      ldr r1, [CONSTPOOL]
      ands r0, r1
    CONSTPOOL: 0xfffffeec

  And now produces:
      movs    r1, #255
      adds    r1, #20  ; Less costly immediate generation
      bics    r0, r1

llvm-svn: 274543

0 files changed, 0 insertions, 0 deletions