[Mlir-commits] [mlir] [mlir][scf] fix getSuccessorRegions func in scf.forall (PR #147491)

[donald chen]

https://github.com/cxy-1993 created https://github.com/llvm/llvm-project/pull/147491

In accordance with the semantics of forall, its body is executed in parallel by multiple threads. We should not expect to branch back into the forall body after the region's execution is complete.

>From bdfb4b04deba41b5c7651de7b7a7e68504ce89c5 Mon Sep 17 00:00:00 2001
From: donald chen <chenxunyu1993 at gmail.com>
Date: Tue, 8 Jul 2025 09:13:26 +0000
Subject: [PATCH] [mlir][scf] fix getSuccessorRegions func in scf.forall

In accordance with the semantics of forall, its body is executed in
parallel by multiple threads. We should not expect to branch back into
the forall body after the region's execution is complete.
---
 mlir/lib/Dialect/SCF/IR/SCF.cpp | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mlir/lib/Dialect/SCF/IR/SCF.cpp b/mlir/lib/Dialect/SCF/IR/SCF.cpp
index 5a3bd984530db..2e0a7b85af756 100644
--- a/mlir/lib/Dialect/SCF/IR/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/IR/SCF.cpp
@@ -1927,11 +1927,13 @@ void ForallOp::getCanonicalizationPatterns(RewritePatternSet &results,
 /// not a constant.
 void ForallOp::getSuccessorRegions(RegionBranchPoint point,
                                    SmallVectorImpl<RegionSuccessor> &regions) {
-  // Both the operation itself and the region may be branching into the body or
-  // back into the operation itself. It is possible for loop not to enter the
-  // body.
-  regions.push_back(RegionSuccessor(&getRegion()));
-  regions.push_back(RegionSuccessor());
+  // In accordance with the semantics of forall, its body is executed in
+  // parallel by multiple threads. We should not expect to branch back into
+  // the forall body after the region's execution is complete.
+  if (point.isParent())
+    regions.push_back(RegionSuccessor(&getRegion()));
+  else
+    regions.push_back(RegionSuccessor());
 }
 
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