[mlir] Fix debug output for passes that modify top-level operation.

[Jezurko]

Make it so that when the top-level (root) operation itself is being modified, it is also used as the root for debug output in PatternApplicator.
Fix #80021

[github-actions]

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be
notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write
permissions for the repository. In which case you can instead tag reviewers by
name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review
by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate
is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

[llvmbot]

@llvm/pr-subscribers-mlir

Author: Robert Konicar (Jezurko)

Changes

Make it so that when the top-level (root) operation itself is being modified, it is also used as the root for debug output in PatternApplicator.
Fix #80021

---

Full diff: https://github.com/llvm/llvm-project/pull/80022.diff

1 Files Affected:

• (modified) mlir/lib/Rewrite/PatternApplicator.cpp (+3-1)

diff --git a/mlir/lib/Rewrite/PatternApplicator.cpp b/mlir/lib/Rewrite/PatternApplicator.cpp
index 0064eb84aba84..686aef2e68e11 100644
--- a/mlir/lib/Rewrite/PatternApplicator.cpp
+++ b/mlir/lib/Rewrite/PatternApplicator.cpp
@@ -40,7 +40,9 @@ static void logImpossibleToMatch(const Pattern &pattern) {
 
 /// Log IR after pattern application.
 static Operation *getDumpRootOp(Operation *op) {
-  return op->getParentWithTrait<mlir::OpTrait::IsIsolatedFromAbove>();
+  return op->hasTrait<mlir::OpTrait::IsIsolatedFromAbove>()
+             ? op
+             : op->getParentWithTrait<mlir::OpTrait::IsIsolatedFromAbove>();
 }
 static void logSucessfulPatternApplication(Operation *op) {
   llvm::dbgs() << "// *** IR Dump After Pattern Application ***\n";

[joker-eph]

If you wish to fix the nullptr, I would likely write it as:

Suggested change

	return op->hasTrait<mlir::OpTrait::IsIsolatedFromAbove>()
	? op
	: op->getParentWithTrait<mlir::OpTrait::IsIsolatedFromAbove>();
	Operation *isolatedParent = op->getParentWithTrait<mlir::OpTrait::IsIsolatedFromAbove>();
	if (isolatedParent) return isolatedParent;
	return op;

(That would preserve the current behavior in general)

[matthias-springer]

This change makes sense to me. If there is no isolated-from-above parent, we are modifying the top-level module and we should dump it directly.

[Jezurko]

You are right, this is better. I have pushed an update