I'm trying to compile some TensorFlow native op with CUDA code. I'm using Python 3.6 and TensorFlow 1.11 here, and CUDA 8.0, on Ubuntu 16.
More specifically:
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.10) GNU C++11 (Ubuntu 5.4.0-6ubuntu1~16.04.10) version 5.4.0 20160609 (x86_64-linux-gnu) compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR version 3.1.4, MPC version 1.0.3 Edit: I repeated the experiment with CUDA 9.0 and CUDA 9.1, and also various compiler backends, via -compiler-bindir clang++ or -compiler-bindir gcc-4.8, and it's always the same error.
test.cu:
// For Eigen::GpuDevice. #define EIGEN_USE_GPU 1 // For Eigen::ThreadPoolDevice. #define EIGEN_USE_THREADS 1 #include "tensorflow/core/framework/op.h" #include "tensorflow/core/framework/shape_inference.h" #include "tensorflow/core/framework/op_kernel.h" #include "tensorflow/core/common_runtime/device.h" #include <cuda.h> #include <cuda_runtime.h> #include <cublas_v2.h> #include <math_constants.h> #include "tensorflow/core/platform/stream_executor.h" Compiling:
$ /usr/local/cuda-8.0/bin/nvcc -shared -O2 -std=c++11 -I /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include -I /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/external/nsync/public -I /usr/local/cuda-8.0/include -L /usr/local/cuda-8.0/lib64 -x cu -DGOOGLE_CUDA=1 -Xcompiler -fPIC -D_GLIBCXX_USE_CXX11_ABI=0 -g test.cu -o test.so -lblas -lf77blas -L/u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/numpy/.libs -lopenblasp-r0-8dca6697.3.0.dev -L/u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow -ltensorflow_framework (Add -v -Xcompiler -v to get some more compiler version info, although that does not seem related here.)
Output:
nvcc warning : The 'compute_20', 'sm_20', and 'sm_21' architectures are deprecated, and may be removed in a future release (Use -Wno-deprecated-gpu-targets to suppress warning). /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/google/protobuf/arena_impl.h(55): warning: integer conversion resulted in a change of sign /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/google/protobuf/arena_impl.h(309): warning: integer conversion resulted in a change of sign /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/google/protobuf/arena_impl.h(310): warning: integer conversion resulted in a change of sign /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/absl/strings/string_view.h(501): error: constexpr function return is non-constant /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1255): warning: calling a constexpr __host__ function("real") from a __host__ __device__ function("abs") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1255): warning: calling a constexpr __host__ function("imag") from a __host__ __device__ function("abs") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1260): warning: calling a constexpr __host__ function("real") from a __host__ __device__ function("abs") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1260): warning: calling a constexpr __host__ function("imag") from a __host__ __device__ function("abs") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1285): warning: calling a constexpr __host__ function("real") from a __host__ __device__ function("exp") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1286): warning: calling a constexpr __host__ function("imag") from a __host__ __device__ function("exp") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1287): warning: calling a constexpr __host__ function("imag") from a __host__ __device__ function("exp") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1293): warning: calling a constexpr __host__ function("real") from a __host__ __device__ function("exp") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1294): warning: calling a constexpr __host__ function("imag") from a __host__ __device__ function("exp") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../../../Eigen/src/Core/MathFunctions.h(1295): warning: calling a constexpr __host__ function("imag") from a __host__ __device__ function("exp") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/tensorflow/core/lib/bfloat16/bfloat16.h(72): warning: calling a constexpr __host__ function("real") from a __host__ __device__ function("bfloat16") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/tensorflow/core/lib/bfloat16/bfloat16.h(75): warning: calling a constexpr __host__ function("real") from a __host__ __device__ function("bfloat16") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this. /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/tensorflow/core/util/tensor_format.h(124): warning: missing return statement at end of non-void function "tensorflow::GetTensorSpatialDims" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/tensorflow/core/util/tensor_format.h(148): warning: missing return statement at end of non-void function "tensorflow::GetTensorDimsFromSpatialDims" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/tensorflow/core/framework/function.h(618): warning: integer conversion resulted in a change of sign /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/tensorflow/core/framework/function.h(619): warning: integer conversion resulted in a change of sign /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(651): warning: missing return statement at end of non-void function "Eigen::internal::igammac_cf_impl<Scalar, mode>::run [with Scalar=float, mode=Eigen::internal::VALUE]" detected during: instantiation of "Scalar Eigen::internal::igammac_cf_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::VALUE]" (855): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::VALUE]" (2096): here instantiation of "Eigen::internal::igamma_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma(const Scalar &, const Scalar &) [with Scalar=float]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsHalf.h(34): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(712): warning: missing return statement at end of non-void function "Eigen::internal::igamma_series_impl<Scalar, mode>::run [with Scalar=float, mode=Eigen::internal::VALUE]" detected during: instantiation of "Scalar Eigen::internal::igamma_series_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::VALUE]" (863): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::VALUE]" (2096): here instantiation of "Eigen::internal::igamma_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma(const Scalar &, const Scalar &) [with Scalar=float]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsHalf.h(34): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(651): warning: missing return statement at end of non-void function "Eigen::internal::igammac_cf_impl<Scalar, mode>::run [with Scalar=float, mode=Eigen::internal::DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igammac_cf_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::DERIVATIVE]" (855): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::DERIVATIVE]" (2102): here instantiation of "Eigen::internal::igamma_der_a_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma_der_a(const Scalar &, const Scalar &) [with Scalar=float]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsHalf.h(38): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(712): warning: missing return statement at end of non-void function "Eigen::internal::igamma_series_impl<Scalar, mode>::run [with Scalar=float, mode=Eigen::internal::DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igamma_series_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::DERIVATIVE]" (863): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::DERIVATIVE]" (2102): here instantiation of "Eigen::internal::igamma_der_a_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma_der_a(const Scalar &, const Scalar &) [with Scalar=float]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsHalf.h(38): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(651): warning: missing return statement at end of non-void function "Eigen::internal::igammac_cf_impl<Scalar, mode>::run [with Scalar=float, mode=Eigen::internal::SAMPLE_DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igammac_cf_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (855): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (2108): here instantiation of "Eigen::internal::gamma_sample_der_alpha_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::gamma_sample_der_alpha(const Scalar &, const Scalar &) [with Scalar=float]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsHalf.h(42): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(712): warning: missing return statement at end of non-void function "Eigen::internal::igamma_series_impl<Scalar, mode>::run [with Scalar=float, mode=Eigen::internal::SAMPLE_DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igamma_series_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (863): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=float, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (2108): here instantiation of "Eigen::internal::gamma_sample_der_alpha_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::gamma_sample_der_alpha(const Scalar &, const Scalar &) [with Scalar=float]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsHalf.h(42): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(651): warning: missing return statement at end of non-void function "Eigen::internal::igammac_cf_impl<Scalar, mode>::run [with Scalar=double, mode=Eigen::internal::VALUE]" detected during: instantiation of "Scalar Eigen::internal::igammac_cf_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::VALUE]" (855): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::VALUE]" (2096): here instantiation of "Eigen::internal::igamma_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma(const Scalar &, const Scalar &) [with Scalar=double]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/arch/CUDA/CudaSpecialFunctions.h(120): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(712): warning: missing return statement at end of non-void function "Eigen::internal::igamma_series_impl<Scalar, mode>::run [with Scalar=double, mode=Eigen::internal::VALUE]" detected during: instantiation of "Scalar Eigen::internal::igamma_series_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::VALUE]" (863): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::VALUE]" (2096): here instantiation of "Eigen::internal::igamma_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma(const Scalar &, const Scalar &) [with Scalar=double]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/arch/CUDA/CudaSpecialFunctions.h(120): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(651): warning: missing return statement at end of non-void function "Eigen::internal::igammac_cf_impl<Scalar, mode>::run [with Scalar=double, mode=Eigen::internal::DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igammac_cf_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::DERIVATIVE]" (855): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::DERIVATIVE]" (2102): here instantiation of "Eigen::internal::igamma_der_a_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma_der_a(const Scalar &, const Scalar &) [with Scalar=double]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/arch/CUDA/CudaSpecialFunctions.h(135): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(712): warning: missing return statement at end of non-void function "Eigen::internal::igamma_series_impl<Scalar, mode>::run [with Scalar=double, mode=Eigen::internal::DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igamma_series_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::DERIVATIVE]" (863): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::DERIVATIVE]" (2102): here instantiation of "Eigen::internal::igamma_der_a_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::igamma_der_a(const Scalar &, const Scalar &) [with Scalar=double]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/arch/CUDA/CudaSpecialFunctions.h(135): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(651): warning: missing return statement at end of non-void function "Eigen::internal::igammac_cf_impl<Scalar, mode>::run [with Scalar=double, mode=Eigen::internal::SAMPLE_DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igammac_cf_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (855): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (2108): here instantiation of "Eigen::internal::gamma_sample_der_alpha_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::gamma_sample_der_alpha(const Scalar &, const Scalar &) [with Scalar=double]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/arch/CUDA/CudaSpecialFunctions.h(154): here /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/SpecialFunctionsImpl.h(712): warning: missing return statement at end of non-void function "Eigen::internal::igamma_series_impl<Scalar, mode>::run [with Scalar=double, mode=Eigen::internal::SAMPLE_DERIVATIVE]" detected during: instantiation of "Scalar Eigen::internal::igamma_series_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (863): here instantiation of "Scalar Eigen::internal::igamma_generic_impl<Scalar, mode>::run(Scalar, Scalar) [with Scalar=double, mode=Eigen::internal::SAMPLE_DERIVATIVE]" (2108): here instantiation of "Eigen::internal::gamma_sample_der_alpha_retval<Eigen::internal::global_math_functions_filtering_base<Scalar, void>::type>::type Eigen::numext::gamma_sample_der_alpha(const Scalar &, const Scalar &) [with Scalar=double]" /u/zeyer/py-envs/py36-tf111/lib/python3.6/site-packages/tensorflow/include/unsupported/Eigen/CXX11/../src/SpecialFunctions/arch/CUDA/CudaSpecialFunctions.h(154): here 1 error detected in the compilation of "/var/tmp/tmpxft_000021f3_00000000-9_test.cpp1.ii". The main error seems to be this:
absl/strings/string_view.h(501): error: constexpr function return is non-constant Looking at that code in string_view.h:
static constexpr size_type CheckLengthInternal(size_type len) { return ABSL_ASSERT(len <= kMaxSize), len; } Where ABSL_ASSERT is defined (in absl/base/macros.h) as:
// ABSL_ASSERT() // // In C++11, `assert` can't be used portably within constexpr functions. // ABSL_ASSERT functions as a runtime assert but works in C++11 constexpr // functions. Example: // // constexpr double Divide(double a, double b) { // return ABSL_ASSERT(b != 0), a / b; // } // // This macro is inspired by // https://akrzemi1.wordpress.com/2017/05/18/asserts-in-constexpr-functions/ #if defined(NDEBUG) #define ABSL_ASSERT(expr) (false ? (void)(expr) : (void)0) #else #define ABSL_ASSERT(expr) \ (ABSL_PREDICT_TRUE((expr)) ? (void)0 \ : [] { assert(false && #expr); }()) // NOLINT #endif Any suggestion what the problem might be? And how to resolve it?
Compiling the same file directly with g++ works. So this is specifically a problem with the nvcc frontend (cudafe).
Edit: I think this might actually be a bug in TensorFlow (or the absl library), so I reported it here. Or it might be a bug in cudafe. (But actually, I think the error looks valid, as this is really not a constant expression, and the ABSL_ASSERT workaround/hack described here might not work here.)