GPU: Raise CUDA/HIP minimum and remove legacy guards

- Raise CUDA minimum from 9.0 to 11.4 (sm_70/Volta).
- Raise HIP minimum to GFX906 (Vega 20/MI50) / ROCm 5.6.
- Remove EIGEN_HAS_{CUDA,HIP,GPU}_FP16 guards — FP16 is always available
  on sm_70+ and GFX906+.
- Remove obsolete __HIP_ARCH_HAS_* preprocessor branches.
- C++14 cleanup: remove pre-C++14 workarounds in GPU code.
- Fix NVCC warnings (deprecated register keyword, unreachable code,
  tautological comparisons).
- Fix HIP test execution on gfx1151.
- Update CI configuration for new minimum versions.

Eigen/src/Core/util/ConfigureVectorization.h

@@ -541,12 +541,6 @@ extern "C" {
 #if defined EIGEN_CUDACC
 #define EIGEN_VECTORIZE_GPU
 #include <vector_types.h>
-#if EIGEN_CUDA_SDK_VER >= 70500
-#define EIGEN_HAS_CUDA_FP16
-#endif
-#endif
-
-#if defined(EIGEN_HAS_CUDA_FP16)
 #include <cuda_runtime_api.h>
 #include <cuda_fp16.h>
 #endif
@@ -554,7 +548,6 @@ extern "C" {
 #if defined(EIGEN_HIPCC)
 #define EIGEN_VECTORIZE_GPU
 #include <hip/hip_vector_types.h>
-#define EIGEN_HAS_HIP_FP16
 #include <hip/hip_fp16.h>
 #define EIGEN_HAS_HIP_BF16
 #include <hip/hip_bfloat16.h>

Eigen/src/Core/util/DisableStupidWarnings.h

@@ -84,8 +84,7 @@
 #endif
 
 #if defined __NVCC__ && defined __CUDACC__
-// MSVC 14.16 (required by CUDA 9.*) does not support the _Pragma keyword, so
-// we instead use Microsoft's __pragma extension.
+// MSVC does not support the _Pragma keyword, so we use Microsoft's __pragma extension.
 #if defined _MSC_VER
 #define EIGEN_MAKE_PRAGMA(X) __pragma(#X)
 #else

Eigen/src/Core/util/Macros.h

@@ -148,13 +148,8 @@
 #endif
 
 #if defined(__NVCC__)
-#if defined(__CUDACC_VER_MAJOR__) && (__CUDACC_VER_MAJOR__ >= 9)
+// CUDA 11.4+ always defines __CUDACC_VER_MAJOR__.
 #define EIGEN_COMP_NVCC ((__CUDACC_VER_MAJOR__ * 10000) + (__CUDACC_VER_MINOR__ * 100))
-#elif defined(__CUDACC_VER__)
-#define EIGEN_COMP_NVCC __CUDACC_VER__
-#else
-#error "NVCC did not define compiler version."
-#endif
 #else
 #define EIGEN_COMP_NVCC 0
 #endif
@@ -575,6 +570,10 @@
 #define EIGEN_CUDA_SDK_VER 0
 #endif
 
+#if defined(EIGEN_CUDACC) && EIGEN_CUDA_SDK_VER > 0 && EIGEN_CUDA_SDK_VER < 110400
+#error "Eigen requires CUDA 11.4 or later."
+#endif
+
 #if defined(__HIPCC__) && !defined(EIGEN_NO_HIP) && !defined(__SYCL_DEVICE_ONLY__)
 // Means the compiler is HIPCC (analogous to EIGEN_CUDACC, but for HIP)
 #define EIGEN_HIPCC __HIPCC__
@@ -584,22 +583,20 @@
 // ++ host_defines.h which contains the defines for the __host__ and __device__ macros
 #include <hip/hip_runtime.h>
 
+// Eigen requires ROCm/HIP >= 5.6 (GFX906 minimum architecture).
+// This floor exists to allow simplifying shared CUDA/HIP preprocessor guards —
+// all __HIP_ARCH_HAS_WARP_SHUFFLE__, __HIP_ARCH_HAS_FP16__, etc. are always true on GFX906+.
+#if defined(HIP_VERSION_MAJOR) && (HIP_VERSION_MAJOR < 5 || (HIP_VERSION_MAJOR == 5 && HIP_VERSION_MINOR < 6))
+#error "Eigen requires ROCm/HIP >= 5.6."
+#endif
+
 #if defined(__HIP_DEVICE_COMPILE__) && !defined(__SYCL_DEVICE_ONLY__)
 // analogous to EIGEN_CUDA_ARCH, but for HIP
 #define EIGEN_HIP_DEVICE_COMPILE __HIP_DEVICE_COMPILE__
 #endif
 
-// For HIP (ROCm 3.5 and higher), we need to explicitly set the launch_bounds attribute
-// value to 1024. The compiler assigns a default value of 256 when the attribute is not
-// specified. This results in failures on the HIP platform, for cases when a GPU kernel
-// without an explicit launch_bounds attribute is called with a threads_per_block value
-// greater than 256.
-//
-// This is a regression in functionality and is expected to be fixed within the next
-// couple of ROCm releases (compiler will go back to using 1024 value as the default)
-//
-// In the meantime, we will use a "only enabled for HIP" macro to set the launch_bounds
-// attribute.
+// HIP compilers default to launch_bounds(256), which causes failures when kernels
+// are called with more than 256 threads per block. Explicitly set to 1024 for HIP.
 
 #define EIGEN_HIP_LAUNCH_BOUNDS_1024 __launch_bounds__(1024)