From 38f89453620eade48d8486483a0ccebfff446f80 Mon Sep 17 00:00:00 2001
From: Yue Huang <30948580+AdUhTkJm@users.noreply.github.com>
Date: Sat, 4 Apr 2026 14:17:57 +0800
Subject: [PATCH] [MLIR][Presburger] Fix stale pivot in Smith normal form
 (#189789)

The pivot used to fix divisibility in Smith normal form is stale. This
will not affect correctness, but can lower efficiency since the outer
loop will be executed more times.

Thanks for @benquike of discovering this.
---
 mlir/lib/Analysis/Presburger/Matrix.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mlir/lib/Analysis/Presburger/Matrix.cpp b/mlir/lib/Analysis/Presburger/Matrix.cpp
index 6ea04543146b..94e9eb5792da 100644
--- a/mlir/lib/Analysis/Presburger/Matrix.cpp
+++ b/mlir/lib/Analysis/Presburger/Matrix.cpp
@@ -653,8 +653,6 @@ IntMatrix::computeSmithNormalForm() const {
         u.negateRow(i);
       }
 
-      DynamicAPInt pivot = d(i, i);
-
       // Clear other entries in row i and column i with Euclid's algorithm.
       for (unsigned r = i + 1; r < numRows; ++r) {
         while (d(r, i) != 0) {
@@ -684,7 +682,7 @@ IntMatrix::computeSmithNormalForm() const {
         }
       }
 
-      if (auto row = findNonMultipleRow(d, i + 1, pivot)) {
+      if (auto row = findNonMultipleRow(d, i + 1, d(i, i))) {
         // Add the row (r) to row i. This brings d(r, c) into the i-th row,
         // creating a new value at d(i, c) that will be used to reduce the
         // pivot size.