[LLVM][SLSR] Add a debug counter

[justinfargnoli]

Add a debug counter to selectively enable or disable SLSR transformations. The debug counter should wrap SLSR's invocation of rewriteCandidateWithBasis().

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See DAGCombiner.cpp for an example use case for a debug counter:

SDValue DAGCombiner::combine(SDNode *N) {
  if (!DebugCounter::shouldExecute(DAGCombineCounter))
      return SDValue();
  ...

See 7a8dc3d for an example of a patch that adds support for a debug counter.

---

Don't feel the need to ask permission to work on this. Just give it a try!

CC @akshayrdeodhar

[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: Justin Fargnoli (justinfargnoli)

Add a debug counter to selectively enable or disable SLSR transformations. The debug counter should wrap `SLSR`'s invocation of [rewriteCandidateWithBasis()](https://github.com/llvm/llvm-project/blob/bd40421ad9ec5ecc164f8208caf3ba5657977e17/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp#L693C7-L693C32).

---

See DAGCombiner.cpp for an example use case for a debug counter:

SDValue DAGCombiner::combine(SDNode *N) {
  if (!DebugCounter::shouldExecute(DAGCombineCounter))
      return SDValue();
  ...

See 7a8dc3d for an example of a patch that adds support for a debug counter.

---

Don't feel the need to ask permission to work on this. Just give it a try!

CC @akshayrdeodhar

[GrumpyPigSkin]

Hi @justinfargnoli ,
I thought this would be an easy first issue, so I have added the debug counter to the file. My issue is how to write a test to ensure it's doing its job.
I had a look at Straight Line Strength Reduction in llvm and it is not immediately obvious to me how the output should be affected by using the counter, so any help would be great :) (or did you just want the functionality added with no test?)

[ParkHanbum]

@GrumpyPigSkin he left a commit link : 7a8dc3d
maybe you can refer it.

[justinfargnoli]

I'd recommend checking out the current state of the DCE debug counter test to understand what kind of test we want to write.

---

Perhaps you could base the test on stride_is_2s. You could check that only the first transformation occurs and the others are skipped.

[GrumpyPigSkin]

Aha okay thanks I’ll have a look. If you want to assign it to me that’d be great, I’m sure I can figure it out with the example's :)

[justinfargnoli]

Also, be sure to check out Adding debug counters to aid in debugging your code.