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


Micah Villmow

Systems Engineer

Advanced Technology & Performance

Advanced Micro Devices Inc.

4555 Great America Pkwy,

Santa Clara, CA. 95054

P: 408-572-6219

F: 408-572-6596

Here's what the comment in X86/X86ISelLowering.h has to say:

    /// computeMaskedBitsForTargetNode - Determine which of the bits
    /// in Mask are known to be either zero or one and return them in
    /// KnownZero/KnownOne bitsets.


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.