**
Revision
367747
by ctopper:
**[InstSimplify] Add test case to show bad sign bit handling for integer abs idiom in computeKnownBits.

computeKnownBits will indicate the sign bit of abs is 0 if the

the RHS operand returned by matchSelectPattern has the nsw flag set.

For abs idioms like (X >= 0) ? X : -X, the RHS returns -X. But

we can also match ((X-Y) >= 0 ? X-Y : Y-X as abs. In this case

RHS will be the Y-X operand. According to Alive, the sign bit for

this is only 0 if both the X-Y and Y-X operands have the nsw flag.

But we're only checking the Y-X operand.