Merge branch 'upstream-Eigen3' into eigen-fork-update-verify-2026-05-10

* upstream-Eigen3:
  Eigen3 2026-05-10 (ae53bfe8)

# Conflicts:
#	Modules/ThirdParty/Eigen3/src/itkeigen/cmake/Eigen3Config.cmake.in

Author: hjmjohnson

Modules/ThirdParty/Eigen3/UpdateFromUpstream.sh

@@ -13,7 +13,7 @@ readonly ownership="Eigen Upstream <kwrobot@kitware.com>"
 exact_tree_match=false
 readonly subtree="Modules/ThirdParty/Eigen3/src/itkeigen"
 readonly repo="https://github.com/InsightSoftwareConsortium/eigen"
-readonly tag="for/itk-20260501-879885e1"
+readonly tag="for/itk-20260509-599d71ab-p2"
 readonly paths="
 Eigen/AccelerateSupport
 Eigen/Cholesky

Modules/ThirdParty/Eigen3/src/itkeigen/CMakeLists.txt

@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: The Eigen Authors
+# SPDX-License-Identifier: MPL-2.0
+
 # Same version of ITK cmake_minimum_required
 cmake_minimum_required(VERSION 3.16.3)
 
@@ -965,6 +968,17 @@ target_include_directories (eigen_internal SYSTEM INTERFACE
 
 # Export as title case Eigen
 set_target_properties (eigen_internal PROPERTIES EXPORT_NAME Eigen)
+# Register in ITK's main export set so find_package(ITK) resolves
+# eigen_internal as an IMPORTED target loaded from ITKTargets.cmake
+# (issue InsightSoftwareConsortium/ITK#6239: SimpleITK FetchContent +
+# FIND_PACKAGE_ARGS fallback). ${ITK3P_INSTALL_EXPORT_NAME} is set by
+# ITK proper in Modules/ThirdParty/Eigen3/src/CMakeLists.txt; if unset
+# (i.e. building outside ITK), this install becomes a no-op.
+if(DEFINED ITK3P_INSTALL_EXPORT_NAME)
+  install (TARGETS eigen_internal EXPORT ${ITK3P_INSTALL_EXPORT_NAME})
+endif()
+# Also register in the standalone ITKInternalEigen3 export set used by
+# find_package(ITKInternalEigen3) consumers.
 install (TARGETS eigen_internal EXPORT ITKInternalEigen3Targets)
 
 set(EIGEN3_TARGETS_FILE ITKInternalEigen3Targets.cmake)

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/AccelerateSupport

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_ACCELERATESUPPORT_MODULE_H
 #define EIGEN_ACCELERATESUPPORT_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Cholesky

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_CHOLESKY_MODULE_H
 #define EIGEN_CHOLESKY_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/CholmodSupport

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_CHOLMODSUPPORT_MODULE_H
 #define EIGEN_CHOLMODSUPPORT_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Core

@@ -7,6 +7,7 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_CORE_MODULE_H
 #define EIGEN_CORE_MODULE_H
@@ -49,7 +50,6 @@
 #include "src/Core/util/MKL_support.h"
 #include "src/Core/util/AOCL_Support.h"
 
-
 // EIGEN_HAS_GPU_FP16 is now always true when compiling with CUDA or HIP.
 // Use EIGEN_GPUCC (compile-time) or EIGEN_GPU_COMPILE_PHASE (device phase) instead.
 // TODO: Remove EIGEN_HAS_GPU_BF16 similarly once HIP bf16 guards are cleaned up.
@@ -152,8 +152,8 @@
 
 namespace Eigen {
 
-using std::size_t;
 using std::ptrdiff_t;
+using std::size_t;
 
 }  // namespace Eigen
 
@@ -275,9 +275,10 @@ using std::ptrdiff_t;
 #include "src/Core/arch/SVE/TypeCasting.h"
 #include "src/Core/arch/SVE/MathFunctions.h"
 #elif defined EIGEN_VECTORIZE_RVV10
+#include "src/Core/arch/RVV10/PacketMathDecl.h"
 #include "src/Core/arch/RVV10/PacketMath.h"
-#include "src/Core/arch/RVV10/PacketMath4.h"
 #include "src/Core/arch/RVV10/PacketMath2.h"
+#include "src/Core/arch/RVV10/PacketMath4.h"
 #include "src/Core/arch/RVV10/TypeCasting.h"
 #include "src/Core/arch/RVV10/MathFunctions.h"
 #if defined EIGEN_VECTORIZE_RVV10FP16
@@ -286,6 +287,10 @@ using std::ptrdiff_t;
 #if defined EIGEN_VECTORIZE_RVV10BF16
 #include "src/Core/arch/RVV10/PacketMathBF16.h"
 #endif
+#if EIGEN_RISCV64_DEFAULT_LMUL == 1
+#include "src/Core/arch/RVV10/Complex.h"
+#include "src/Core/arch/RVV10/Complex2.h"
+#endif
 #elif defined EIGEN_VECTORIZE_ZVECTOR
 #include "src/Core/arch/ZVector/PacketMath.h"
 #include "src/Core/arch/ZVector/MathFunctions.h"

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Dense

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_DENSE_MODULE_H
 #define EIGEN_DENSE_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Eigen

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_EIGEN_MODULE_H
 #define EIGEN_EIGEN_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Eigenvalues

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_EIGENVALUES_MODULE_H
 #define EIGEN_EIGENVALUES_MODULE_H

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/Geometry

@@ -4,6 +4,8 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-FileCopyrightText: The Eigen Authors
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_GEOMETRY_MODULE_H
 #define EIGEN_GEOMETRY_MODULE_H
@@ -23,7 +25,8 @@
  *  - \link Quaternion quaternions \endlink
  *  - cross products (\ref MatrixBase::cross(), \ref MatrixBase::cross3())
  *  - orthogonal vector generation (MatrixBase::unitOrthogonal)
- *  - some linear components: \link ParametrizedLine parametrized-lines \endlink and \link Hyperplane hyperplanes \endlink
+ *  - some linear components: \link ParametrizedLine parametrized-lines \endlink and \link Hyperplane hyperplanes
+ * \endlink
  *  - \link AlignedBox axis aligned bounding boxes \endlink
  *  - \link umeyama() least-square transformation fitting \endlink
  * \code