[LLVMdev] SimplifyDemandedUseBits vs (and (xor %V, -1), 4096)

[David Majnemer]

SimplifyDemandedUseBits in part because of the following comment:

// FIXME: for XOR, we prefer to force bits to 1 if they will make a -1.

will transform

%neg = xor i32 %V, -1
%and = and i32 %not, 4096

into

%and = and i32 %V, 4096
%xor = xor i32 %and, 4096

which would generate worse code for platforms that have a negate
instruction vs. encoding the immediate in the xor.

What should happen to the code to address the FIXME?

Thanks
-- 
David Majnemer
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130414/363c516a/attachment.html>