To go along with sabre's improved InstCombining, improve recognition of

integers that we can use as immediate values in instructions.

Example from yacr2:
-       lis r10, -1
-       ori r10, r10, 65535
-       add r28, r28, r10
+       addi r28, r28, -1
        addi r7, r7, 1
        addi r9, r9, 1
        b .LBB_main_9   ; loopentry.1.i214

llvm-svn: 16566