This commit contains the following (HIP specific) updates:

- unsupported/Eigen/CXX11/src/Tensor/TensorReductionGpu.h
  Changing "pass-by-reference" argument to be "pass-by-value" instead
  (in a  __global__ function decl).
  "pass-by-reference" arguments to __global__ functions are unwise,
  and will be explicitly flagged as errors by the newer versions of HIP.

- Eigen/src/Core/util/Memory.h
- unsupported/Eigen/CXX11/src/Tensor/TensorContraction.h
  Changes introduced in recent commits breaks the HIP compile.
  Adding EIGEN_DEVICE_FUNC attribute to some functions and
  calling ::malloc/free instead of the corresponding std:: versions
  to get the HIP compile working again

- unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h
  Change introduced a recent commit breaks the HIP compile
  (link stage errors out due to failure to inline a function).
  Disabling the recently introduced code (only for HIP compile), to get
  the eigen nightly testing going again.
  Will submit another PR once we have te proper fix.

- Eigen/src/Core/util/ConfigureVectorization.h
  Enabling GPU VECTOR support when HIP compiler is in use
  (for both the host and device compile phases)

Eigen/src/Core/util/ConfigureVectorization.h

@@ -379,10 +379,12 @@
   #include <cuda_fp16.h>
 #endif
 
-#if defined(EIGEN_HIP_DEVICE_COMPILE)
-
+#if defined(EIGEN_HIPCC)
   #define EIGEN_VECTORIZE_GPU
   #include <hip/hip_vector_types.h>
+#endif
+
+#if defined(EIGEN_HIP_DEVICE_COMPILE)
 
   #define EIGEN_HAS_HIP_FP16
   #include <hip/hip_fp16.h>

Eigen/src/Core/util/Memory.h

@@ -96,10 +96,16 @@ inline void throw_std_bad_alloc()
 /** \internal Like malloc, but the returned pointer is guaranteed to be 16-byte aligned.
   * Fast, but wastes 16 additional bytes of memory. Does not throw any exception.
   */
-inline void* handmade_aligned_malloc(std::size_t size, std::size_t alignment = EIGEN_DEFAULT_ALIGN_BYTES)
+EIGEN_DEVICE_FUNC inline void* handmade_aligned_malloc(std::size_t size, std::size_t alignment = EIGEN_DEFAULT_ALIGN_BYTES)
 {
   eigen_assert(alignment >= sizeof(void*) && (alignment & -alignment) == alignment && "Alignment must be at least sizeof(void*) and a power of 2");
+  
+#if defined(EIGEN_HIP_DEVICE_COMPILE)
+  void *original = ::malloc(size+alignment);
+#else
   void *original = std::malloc(size+alignment);
+#endif
+  
   if (original == 0) return 0;
   void *aligned = reinterpret_cast<void*>((reinterpret_cast<std::size_t>(original) & ~(std::size_t(alignment-1))) + alignment);
   *(reinterpret_cast<void**>(aligned) - 1) = original;
@@ -107,9 +113,15 @@ inline void* handmade_aligned_malloc(std::size_t size, std::size_t alignment = E
 }
 
 /** \internal Frees memory allocated with handmade_aligned_malloc */
-inline void handmade_aligned_free(void *ptr)
+EIGEN_DEVICE_FUNC inline void handmade_aligned_free(void *ptr)
 {
-  if (ptr) std::free(*(reinterpret_cast<void**>(ptr) - 1));
+  if (ptr) {
+#if defined(EIGEN_HIP_DEVICE_COMPILE)
+    ::free(*(reinterpret_cast<void**>(ptr) - 1));
+#else
+    std::free(*(reinterpret_cast<void**>(ptr) - 1));
+#endif
+  }
 }
 
 /** \internal