[Mlir-commits] [mlir] [mlir][Transforms] Dialect Conversion: `allowPatternRollback` to check foldings (PR #148394)

[Matthias Springer]

https://github.com/matthias-springer created https://github.com/llvm/llvm-project/pull/148394

When an operation is folded to an attribute, the attribute must be materialized as a constant operation. That operation must then be legalized. If such a legalization fails, the entire folding is rolled back. This is not supported in a One-Shot Dialect Conversion.

This commit improves the `allowPatternRollback` flag handling, such that a fatal error is reported when a folder is attempted to be rolled back.



>From 886438865e2656fdbb135882729e6133bdc8f47e Mon Sep 17 00:00:00 2001
From: Matthias Springer <me at m-sp.org>
Date: Sat, 12 Jul 2025 18:54:39 +0000
Subject: [PATCH] [mlir][Transforms] Dialect Conversion: `allowPatternRollback`
 to check foldings

---
 mlir/lib/Transforms/Utils/DialectConversion.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mlir/lib/Transforms/Utils/DialectConversion.cpp b/mlir/lib/Transforms/Utils/DialectConversion.cpp
index 9f71129d39d09..437dbcfea5288 100644
--- a/mlir/lib/Transforms/Utils/DialectConversion.cpp
+++ b/mlir/lib/Transforms/Utils/DialectConversion.cpp
@@ -2176,6 +2176,7 @@ OperationLegalizer::legalizeWithFold(Operation *op,
   (void)rewriterImpl;
 
   // Try to fold the operation.
+  StringRef opName = op->getName().getStringRef();
   SmallVector<Value, 2> replacementValues;
   SmallVector<Operation *, 2> newOps;
   rewriter.setInsertionPoint(op);
@@ -2195,6 +2196,12 @@ OperationLegalizer::legalizeWithFold(Operation *op,
       LLVM_DEBUG(logFailure(rewriterImpl.logger,
                             "failed to legalize generated constant '{0}'",
                             newOp->getName()));
+      if (!config.allowPatternRollback) {
+        // Rolling back a folder is like rolling back a pattern.
+        llvm::report_fatal_error(
+            "op '" + opName +
+            "' folder rollback of IR modifications requested");
+      }
       // Legalization failed: erase all materialized constants.
       for (Operation *op : newOps)
         rewriter.eraseOp(op);