[PATCH] D38415: [SimplifyIndVar] Replace IVUsers with loop invariant if possible

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


================
Comment at: lib/Transforms/Utils/SimplifyIndVar.cpp:552
 
-  if (!C)
+  if (!SE->isLoopInvariant(S, L))
     return false;
----------------
etherzhhb wrote:
> efriedma wrote:
> > etherzhhb wrote:
> > > We may only want to do the replace if S is invariant of the IV's Loop, which may be different from "L" which is the innermost loop that contains the IV user
> > Yes; otherwise, the transform isn't doing anything useful.
> > 
> > We might need to call isHighCostExpansion here, so we don't generate something ridiculous?
> Yes, this make sense.
> 
> I did some experiments and we may want to actually write:
> 
> ```
> if (!SE->isLoopInvariant(S, IV's Loop) || !SE->isLoopInvariant(S, IV User's Loop))
> ```
> 
> If IV's Loop do not contains IV User's Loop
Given a function in LCSSA form, I don't think this relevant?  But feel free to prove me wrong. :)


https://reviews.llvm.org/D38415