[Mlir-commits] [mlir] [mlir][SCF] Add pass option to deactivate pattern rollback (PR #168481)

[Matthias Springer]

https://github.com/matthias-springer created https://github.com/llvm/llvm-project/pull/168481

Add a pass option to `convert-scf-to-cf` to deactivate pattern rollback for better performance. The lowering patterns from SCF->CF to benefit a lot from this feature because `splitBlock` is expensive in the rollback driver.


>From 45279a48fc1bbbf7c233423cf92cc6aff946f872 Mon Sep 17 00:00:00 2001
From: Matthias Springer <me at m-sp.org>
Date: Tue, 18 Nov 2025 04:52:06 +0000
Subject: [PATCH] [mlir][SCF] Add pass option to deactivate pattern rollback

---
 mlir/include/mlir/Conversion/Passes.td                    | 4 ++++
 mlir/lib/Conversion/SCFToControlFlow/SCFToControlFlow.cpp | 7 +++++--
 mlir/test/Conversion/SCFToControlFlow/convert-to-cfg.mlir | 1 +
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/mlir/include/mlir/Conversion/Passes.td b/mlir/include/mlir/Conversion/Passes.td
index 79bc380dbcb7a..ca2ed2947b8e0 100644
--- a/mlir/include/mlir/Conversion/Passes.td
+++ b/mlir/include/mlir/Conversion/Passes.td
@@ -1084,6 +1084,10 @@ def SCFToControlFlowPass : Pass<"convert-scf-to-cf"> {
   let summary = "Convert SCF dialect to ControlFlow dialect, replacing structured"
                 " control flow with a CFG";
   let dependentDialects = ["cf::ControlFlowDialect"];
+  let options = [
+    Option<"allowPatternRollback", "allow-pattern-rollback", "bool", "true",
+           "Experimental performance flag to disallow pattern rollback">
+  ];
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/Conversion/SCFToControlFlow/SCFToControlFlow.cpp b/mlir/lib/Conversion/SCFToControlFlow/SCFToControlFlow.cpp
index 37cfc9f2c23e6..03842cc9bd3a0 100644
--- a/mlir/lib/Conversion/SCFToControlFlow/SCFToControlFlow.cpp
+++ b/mlir/lib/Conversion/SCFToControlFlow/SCFToControlFlow.cpp
@@ -36,6 +36,7 @@ namespace {
 
 struct SCFToControlFlowPass
     : public impl::SCFToControlFlowPassBase<SCFToControlFlowPass> {
+  using Base::Base;
   void runOnOperation() override;
 };
 
@@ -736,7 +737,9 @@ void SCFToControlFlowPass::runOnOperation() {
   target.addIllegalOp<scf::ForallOp, scf::ForOp, scf::IfOp, scf::IndexSwitchOp,
                       scf::ParallelOp, scf::WhileOp, scf::ExecuteRegionOp>();
   target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
-  if (failed(
-          applyPartialConversion(getOperation(), target, std::move(patterns))))
+  ConversionConfig config;
+  config.allowPatternRollback = allowPatternRollback;
+  if (failed(applyPartialConversion(getOperation(), target, std::move(patterns),
+                                    config)))
     signalPassFailure();
 }
diff --git a/mlir/test/Conversion/SCFToControlFlow/convert-to-cfg.mlir b/mlir/test/Conversion/SCFToControlFlow/convert-to-cfg.mlir
index 483c7b35c6ec8..0c4f20e8d1a04 100644
--- a/mlir/test/Conversion/SCFToControlFlow/convert-to-cfg.mlir
+++ b/mlir/test/Conversion/SCFToControlFlow/convert-to-cfg.mlir
@@ -1,4 +1,5 @@
 // RUN: mlir-opt -allow-unregistered-dialect -convert-scf-to-cf -split-input-file %s | FileCheck %s
+// RUN: mlir-opt -allow-unregistered-dialect -convert-scf-to-cf="allow-pattern-rollback=0" -split-input-file %s | FileCheck %s
 
 // CHECK-LABEL: func @simple_std_for_loop(%{{.*}}: index, %{{.*}}: index, %{{.*}}: index) {
 //  CHECK-NEXT:  cf.br ^bb1(%{{.*}} : index)