assigned to @lattner

i.e. this example shows that replacing ult with slt (and presumably
vice-versa) can be advantageous, but this is not exploited.

I forgot to mention where this comes from: the gcc -> llvm switch
conversion code lowers wide case ranges to explicit conditional
branches. The test that x is in the range lo .. hi is emitted as
"x-lo ule hi-lo". If lo is INT_MIN then this results in suboptimal
code, as explained in this PR. I could have checked for this case
explicitly in the switch conversion code, but I didn't want to do so
because it is really a job for the optimizers: they should be able to
handle this case. Oddly enough, if you emit the test as "(x>=lo)&&(x<=hi)"
then it gets simplified optimally.

Fixed, testcase here: Transforms/InstCombine/xor2.ll:test[01]
Patch here:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070402/046701.html

This handles the general case of a xor constant, not just this specific one.

-Chris