From b3c4344a6852e55c849976dd46ec4e861399bf16 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Thu, 7 Feb 2019 15:21:35 +0100
Subject: bug #1676: workaround GCC's bug in c++17 mode.

---
 Eigen/src/Core/DenseBase.h                | 4 ++--
 Eigen/src/Core/util/ForwardDeclarations.h | 6 +-----
 bench/bench_gemm.cpp                      | 5 +++--
 3 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/Eigen/src/Core/DenseBase.h b/Eigen/src/Core/DenseBase.h
index 65ec1f54b..406e66013 100644
--- a/Eigen/src/Core/DenseBase.h
+++ b/Eigen/src/Core/DenseBase.h
@@ -40,7 +40,7 @@ static inline void check_DenseIndex_is_signed() {
   */
 template<typename Derived> class DenseBase
 #ifndef EIGEN_PARSED_BY_DOXYGEN
-  : public DenseCoeffsBase<Derived>
+  : public DenseCoeffsBase<Derived, internal::accessors_level<Derived>::value>
 #else
   : public DenseCoeffsBase<Derived,DirectWriteAccessors>
 #endif // not EIGEN_PARSED_BY_DOXYGEN
@@ -71,7 +71,7 @@ template<typename Derived> class DenseBase
     typedef Scalar value_type;
     
     typedef typename NumTraits<Scalar>::Real RealScalar;
-    typedef DenseCoeffsBase<Derived> Base;
+    typedef DenseCoeffsBase<Derived, internal::accessors_level<Derived>::value> Base;
 
     using Base::derived;
     using Base::const_cast_derived;
diff --git a/Eigen/src/Core/util/ForwardDeclarations.h b/Eigen/src/Core/util/ForwardDeclarations.h
index 5d86a51ac..050d15e96 100644
--- a/Eigen/src/Core/util/ForwardDeclarations.h
+++ b/Eigen/src/Core/util/ForwardDeclarations.h
@@ -47,11 +47,7 @@ template<typename T> struct NumTraits;
 template<typename Derived> struct EigenBase;
 template<typename Derived> class DenseBase;
 template<typename Derived> class PlainObjectBase;
-
-
-template<typename Derived,
-         int Level = internal::accessors_level<Derived>::value >
-class DenseCoeffsBase;
+template<typename Derived, int Level> class DenseCoeffsBase;
 
 template<typename _Scalar, int _Rows, int _Cols,
          int _Options = AutoAlign |
diff --git a/bench/bench_gemm.cpp b/bench/bench_gemm.cpp
index 688d99c4a..7c6dbea61 100644
--- a/bench/bench_gemm.cpp
+++ b/bench/bench_gemm.cpp
@@ -112,6 +112,7 @@ void matlab_cplx_cplx(const M& ar, const M& ai, const M& br, const M& bi, M& cr,
   cr.noalias() -= ai * bi;
   ci.noalias() += ar * bi;
   ci.noalias() += ai * br;
+  // [cr ci] += [ar ai] * br + [-ai ar] * bi
 }
 
 void matlab_real_cplx(const M& a, const M& br, const M& bi, M& cr, M& ci)
@@ -240,7 +241,7 @@ int main(int argc, char ** argv)
     blas_gemm(a,b,r);
     c.noalias() += a * b;
     if(!r.isApprox(c)) {
-      std::cout << r  - c << "\n";
+      std::cout << (r  - c).norm() << "\n";
       std::cerr << "Warning, your product is crap!\n\n";
     }
   #else
@@ -249,7 +250,7 @@ int main(int argc, char ** argv)
       gemm(a,b,c);
       r.noalias() += a.cast<Scalar>() .lazyProduct( b.cast<Scalar>() );
       if(!r.isApprox(c)) {
-        std::cout << r - c << "\n";
+        std::cout << (r  - c).norm() << "\n";
         std::cerr << "Warning, your product is crap!\n\n";
       }
     }
-- 
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