[PATCH] D48853: [SCEV] Add zext(C + x + ...) -> D + zext(C-D + x + ...)<nuw> transform

[Roman Tereshin via Phabricator via llvm-commits]

rtereshin added inline comments.


================
Comment at: test/Analysis/ScalarEvolution/no-wrap-add-exprs.ll:150
+; CHECK:  %p1.zext = zext i8 %p1 to i16
+; CHECK-NEXT:  -->  (zext i8 (8 + (4 * %x)) to i16) U: [0,253) S: [0,256)
+
----------------
mkazantsev wrote:
> Its weird. Why signed and unsigned ranges are different?
That's a good question. One thing I know is that the issue is orthogonal to this patch and exists on trunk:

```
  %p1.zext = zext i8 %p1 to i16
  -->  (zext i8 (8 + (4 * %x)) to i16) U: [0,253) S: [0,256)
```
(this is w/o this patch applied)

Perhaps unsigned range takes some knownbits-like information into account, while signed one doesn't.


Repository:
  rL LLVM

https://reviews.llvm.org/D48853