[LLVMdev] computeMaskedBitsforTargetNode

[Eli Friedman]

On Thu, Nov 20, 2008 at 6:19 PM, Villmow, Micah <Micah.Villmow at amd.com> wrote:
> Can someone explain what this function is supposed to do? I've looked at
> PowerPC, Sparc, etc.. and can't really figure out what I should be doing
> here.

It's an optimization: it allows the target-independent passes like
DAGCombine to get information about which bits of a value are known at
compile-time to be set or known to be unset.  The conservative
assumption is that nothing is known, so the default implementation is
always correct.

-Eli