There is already indication that this has occurred:

Optimize integral reciprocal (udiv 1, x and sdiv 1, x) to not use division: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-...

Optimize signed icmp of -(zext V): http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-...

Optimize -x s< cst: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-...

What's neat is that not all of these end up needing the InstCombine pass to get optimized, some of them can be handled using InstSimplify. InstSimplify isn't a pass, it's an analysis that get's called upon many times in the middle of other passes, strengthening them.