From 6f40e8a5a86d2c97db46ec5e531fc97744737355 Mon Sep 17 00:00:00 2001
From: "Hans J. Johnson" <hans-johnson@uiowa.edu>
Date: Wed, 29 Apr 2026 19:57:21 -0500
Subject: [PATCH] COMP: Use pzero() init for Packet locals in
 SelfadjointMatrixVector loop

Follow-up to #6166. On ubuntu-24.04 + GCC 13/14 + C++20 (the toolchain
that #6164 introduces), GCC -O3 IPA-CP emits additional false-positive
-Wmaybe-uninitialized at the outer selfadjoint_product_impl::run()
call site, attributing the read to "argument 3 of type const float *"
of the cloned selfadjoint_matrix_vector_product::run.constprop.isra.

Add pzero(Packet{}) declare-then-assign init for the four Packet
locals (A0i, A1i, Bi, Xi) loaded from the lhs/rhs/res pointers inside
the inner loop. Mirrors the #6166 ptmp2/ptmp3 pattern: pzero() is
visible to GCC's IPA-CP as a definite zero starting state, while a
bare declaration plus subsequent ploadu/pload is opaque and lets the
optimizer trace an uninit path through cloned variants.
---
 .../src/Core/products/SelfadjointMatrixVector.h      | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/src/Core/products/SelfadjointMatrixVector.h b/Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/src/Core/products/SelfadjointMatrixVector.h
index 6e3c0dc6fe0..912b579c576 100644
--- a/Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/src/Core/products/SelfadjointMatrixVector.h
+++ b/Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/src/Core/products/SelfadjointMatrixVector.h
@@ -112,13 +112,17 @@ selfadjoint_matrix_vector_product<Scalar, Index, StorageOrder, UpLo, ConjugateLh
     const Scalar* EIGEN_RESTRICT rhsIt = rhs + alignedStart;
     Scalar* EIGEN_RESTRICT resIt = res + alignedStart;
     for (Index i = alignedStart; i < alignedEnd; i += PacketSize) {
-      Packet A0i = ploadu<Packet>(a0It);
+      Packet A0i = pzero(Packet{});
+      A0i = ploadu<Packet>(a0It);
       a0It += PacketSize;
-      Packet A1i = ploadu<Packet>(a1It);
+      Packet A1i = pzero(Packet{});
+      A1i = ploadu<Packet>(a1It);
       a1It += PacketSize;
-      Packet Bi = ploadu<Packet>(rhsIt);
+      Packet Bi = pzero(Packet{});
+      Bi = ploadu<Packet>(rhsIt);
       rhsIt += PacketSize;  // FIXME should be aligned in most cases
-      Packet Xi = pload<Packet>(resIt);
+      Packet Xi = pzero(Packet{});
+      Xi = pload<Packet>(resIt);
 
       Xi = pcj0.pmadd(A0i, ptmp0, pcj0.pmadd(A1i, ptmp1, Xi));
       ptmp2 = pcj1.pmadd(A0i, Bi, ptmp2);