[CVP] Failure to recognise trunc nsw from assumptions

[RKSimon]

Pulled out of #130088

----------------------------------------
define i8 @src(i16 noundef %x) {
#0:
  %add = add i16 noundef %x, 128
  %or.cond.i = icmp ult i16 %add, 256
  assume i1 %or.cond.i
  %conv1 = trunc i16 noundef %x to i8
  ret i8 %conv1
}
=>
define i8 @tgt(i16 noundef %x) {
#0:
  %conv1 = trunc nsw i16 noundef %x to i8
  ret i8 %conv1
}
Transformation seems to be correct!

https://alive2.llvm.org/ce/z/2qhZy4

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
2. In the comments of this issue, request for it to be assigned to you, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

Pulled out of #130088 ```ll ---------------------------------------- define i8 @src(i16 noundef %x) { #0: %add = add i16 noundef %x, 128 %or.cond.i = icmp ult i16 %add, 256 assume i1 %or.cond.i %conv1 = trunc i16 noundef %x to i8 ret i8 %conv1 } => define i8 @tgt(i16 noundef %x) { #0: %conv1 = trunc nsw i16 noundef %x to i8 ret i8 %conv1 } Transformation seems to be correct! ``` https://alive2.llvm.org/ce/z/2qhZy4

[bababuck]

@dtcxzyw Can iI give this a go if no one else is already working on it?

[ArunaHulakoti]

@llvmbot Could you please provide more details on the expected behavior?

[dtcxzyw]

@dtcxzyw Can iI give this a go if no one else is already working on it?

Sorry to tell you that this issue is covered by #130504.

[veera-sivarajan]

@bababuck sorry, I didn't know you were assigned to this.