[PATCH] D34278: [InstCombine] Recognize and simplify three way comparison idioms

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:2495
+    Value *Cond = Builder->getFalse();
+    if (TrueWhenLessThan)
+      Cond = Builder->CreateOr(Cond, Builder->CreateICmp(ICmpInst::ICMP_SLT, OrigLHS, OrigRHS));
----------------
anna wrote:
> mkazantsev wrote:
> > Is it possible that more than one of {TrueWhenLessThan, TrueWhenEqual, TrueWhenGreaterThan} is true?
> > 
> > If no, please add an assertion on that and use "else if" below.
> > If yes, should we not consider this when creating conditions?
> Yes, more than one can be true at a time: this actually enumerates all the possible 8 combinations, because of the chaining of these ORs in `CreateOr`. We pass in the `Cond` as the parameter. 
> 
> (I actually liked this idea a lot: credit goes to Sanjoy in suggesting this in the original review).
> 
> Please see the comment above the code, should I perhaps clarify it more? 
> 
> 
I've re-read the comment and the code, and I think it's fine, I just didn't realize the idea from the very beginning.


https://reviews.llvm.org/D34278