[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:
> > 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


https://reviews.llvm.org/D38415