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

[Hongbin Zheng via Phabricator via llvm-commits]

etherzhhb added inline comments.


================
Comment at: lib/Transforms/Utils/SimplifyIndVar.cpp:552
 
-  if (!C)
+  if (!SE->isLoopInvariant(S, L))
     return false;
----------------
efriedma wrote:
> 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. :)
Not sure if we assume LCSSA (or SCEV could see through it), I hit some crash when I just test 'if (!SE->isLoopInvariant(S, IV's Loop))' and it turned out that IV's Loop do not contain IV's user. I will find those cases


https://reviews.llvm.org/D38415