The dream of a unified check-line auto-generator for all phases of compilation is dead.
The llc script has already diverged to be better at its goal, so having 2 scripts that
do almost the same thing is just causing confusion.
We can rip out the llc ability in update_test_checks.py next and rename it, so it will
be clear that we have one script for llc check auto-generation and another for opt.
llvm-svn: 305206
We treat bitwise 'not' as a special operation and try not to reduce its all-ones mask.
Presumably, this is because a 'not' may be cheaper than a generic 'xor' or it may get
folded into another logic op if the target has those. However, if we can remove a logic
instruction by changing the xor's constant mask value, that should always be a win.
Note that the IR version of SimplifyDemandedBits() does not treat 'not' as a special-case
currently (although that's marked with a FIXME). So if you run this IR through -instcombine,
you should get the same end result. I'm hoping to add a different backend transform that
will expose this problem though, so I need to solve this first.
Differential Revision: https://reviews.llvm.org/D27356
llvm-svn: 288676
Sanjay Patel