[PATCH] D14175: [SCEV] Generalize the SCEV algorithm for creating expressions for PHI nodes

[Sanjoy Das via llvm-commits]

sanjoy requested changes to this revision.
sanjoy added a comment.
This revision now requires changes to proceed.

Overall, looks good.  I just have one comment inline.


================
Comment at: lib/Analysis/ScalarEvolution.cpp:3818
@@ +3817,3 @@
+      // by one iteration.
+      const SCEV *Shifted = SCEVShiftRewriter::rewrite(BEValue, L, *this);
+      const SCEV *Start = SCEVInitRewriter::rewrite(Shifted, L, *this);
----------------
Why not do `{A,+,B}` => `(A-B)` as a single transform?

Also, a nice way to document this rule is (totally up to you if you like this language):

```
PHI(f(I), f({I+S,+,S})) --> f({I,+,S})
```



http://reviews.llvm.org/D14175