As discussed on D77804, instcombine will have already performed a similar SimplifyMultipleUseDemandedBits call which will break the UXTB16 pattern that was being match in these DAG tests
I've updated the existing tests so that it match the instcombine IR (with a suitable FIXME) and added an equivalent test pattern suggested by @dmgreen
Replace the use of grep with FileCheck. Tidy up some of the tests. A
few of the tests have been left as weak as previously, though some have
been made more stringent.
llvm-svn: 290616
