From d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0 Mon Sep 17 00:00:00 2001
From: Alex Druinsky <adruinsky@google.com>
Date: Wed, 20 Oct 2021 16:03:12 -0700
Subject: [PATCH] Fix vectorized reductions for Eigen::half

Fixes compiler errors in expressions that look like

  Eigen::Matrix<Eigen::half, 3, 1>::Random().maxCoeff()

The error comes from the code that creates the initial value for
vectorized reductions. The fix is to specify the scalar type of the
reduction's initial value.

The cahnge is necessary for Eigen::half because unlike other types,
Eigen::half scalars cannot be implicitly created from integers.
---
 Eigen/src/Core/PartialReduxEvaluator.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Eigen/src/Core/PartialReduxEvaluator.h b/Eigen/src/Core/PartialReduxEvaluator.h
index 4040ae726f..a179688815 100644
--- a/Eigen/src/Core/PartialReduxEvaluator.h
+++ b/Eigen/src/Core/PartialReduxEvaluator.h
@@ -56,12 +56,17 @@ struct packetwise_redux_traits
 /* Value to be returned when size==0 , by default let's return 0 */
 template<typename PacketType,typename Func>
 EIGEN_DEVICE_FUNC
-PacketType packetwise_redux_empty_value(const Func& ) { return pset1<PacketType>(0); }
+PacketType packetwise_redux_empty_value(const Func& ) {
+  const typename unpacket_traits<PacketType>::type zero(0);
+  return pset1<PacketType>(zero);
+}
 
 /* For products the default is 1 */
 template<typename PacketType,typename Scalar>
 EIGEN_DEVICE_FUNC
-PacketType packetwise_redux_empty_value(const scalar_product_op<Scalar,Scalar>& ) { return pset1<PacketType>(1); }
+PacketType packetwise_redux_empty_value(const scalar_product_op<Scalar,Scalar>& ) {
+  return pset1<PacketType>(Scalar(1));
+}
 
 /* Perform the actual reduction */
 template<typename Func, typename Evaluator,
-- 
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