Disable the (A == (B-A)) -> 2*A == B xform when the sub has multiple uses (in

this case, the xform introduces an extra operation).  This compiles
PowerPC/compare-duplicate.ll into:

_test:
        subf r2, r3, r4
        cmplw cr0, r2, r3
        bne cr0, LBB1_2 ;F

instead of:

_test:
        slwi r2, r3, 1
        subf r3, r3, r4
        cmplw cr0, r4, r2
        bne cr0, LBB1_2 ;F

This is target independent of course.

llvm-svn: 37246