commit 24471f62b41da451ca990bf2e3d00f63adb281a1
author Matthias Springer <me@m-sp.org> Mon Sep 29 08:05:59 2025 +0000
committer Matthias Springer <me@m-sp.org> Tue Sep 30 10:44:43 2025 +0000
tree 69853c9fa302ed72f7695766e6f8d982307fb469
parent 2284ce0596ecd66849099f4918f726f8e27607aa

[mlir][Transforms] Greedy pattern rewriter: fix infinite folding loop

mlir/lib/Dialect/Arith/IR/ArithOps.cpp

diff --git a/mlir/lib/Dialect/Arith/IR/ArithOps.cpp b/mlir/lib/Dialect/Arith/IR/ArithOps.cpp
index 7cfd6d3..04daed8c 100644
--- a/mlir/lib/Dialect/Arith/IR/ArithOps.cpp
+++ b/mlir/lib/Dialect/Arith/IR/ArithOps.cpp
@@ -393,7 +393,7 @@
 
 OpFoldResult arith::AddIOp::fold(FoldAdaptor adaptor) {
   // addi(x, 0) -> x
-  if (matchPattern(adaptor.getRhs(), m_Zero()))
+  if (matchPattern(adaptor.getRhs(), m_Zero()) && getLhs() != *this)
     return getLhs();
 
   // addi(subi(a, b), b) -> a

mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp

diff --git a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
index 74e4a82..93468dd 100644
--- a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
+++ b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
@@ -555,7 +555,8 @@
           replacements.push_back(constOp->getResult(0));
         }
 
-        if (materializationSucceeded) {
+        if (materializationSucceeded &&
+            !llvm::equal(replacements, op->getResults())) {
           rewriter.replaceOp(op, replacements);
           changed = true;
           LLVM_DEBUG(logSuccessfulFolding(dumpRootOp));

mlir/test/Transforms/canonicalize.mlir

diff --git a/mlir/test/Transforms/canonicalize.mlir b/mlir/test/Transforms/canonicalize.mlir
index 8e02c06..ed987e5 100644
--- a/mlir/test/Transforms/canonicalize.mlir
+++ b/mlir/test/Transforms/canonicalize.mlir
@@ -1248,3 +1248,12 @@
   %u = index.castu %const : index to i64
   return %u: i64
 }
+
+// -----
+
+// Make sure that the canonicalizer does not fold infinitely.
+
+// CHECK: %[[c0:.*]] = arith.constant 0 : index
+%c0 = arith.constant 0 : index
+// CHECK: %[[add:.*]] = arith.addi %[[c0]], %[[add]] : index
+%0 = arith.addi %c0, %0 : index