...into (ashr (shl (anyext X), ...), ...), which requires one fewer
instruction. The (anyext X) can sometimes be simplified too.
I didn't do this in DAGCombiner because widening shifts isn't a win
on all targets.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199114 91177308-0d34-0410-b5e6-96231b3b80d8
The input to an RxSBG operation can be narrower as long as the upper bits
are don't care. This fixes a FIXME added in r192783.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192790 91177308-0d34-0410-b5e6-96231b3b80d8
This is really an extension of the current (shl (shr ...)) -> shl optimization.
The main difference is that certain upper bits must also not be demanded.
The motivating examples are the first two in the testcase, which occur
in llvmpipe output.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192783 91177308-0d34-0410-b5e6-96231b3b80d8
