spmv: template arguments not always inferrable

[brian-kelley]

For a call like KokkosSparse::spmv(space, mode, alpha, A, x, beta, y);, template argument deduction fails.

[lucbv]

I am wondering if in @e10harvey 's case the issue is related to wrapping the execution space in a std::vector.
This might somehow hide the underlying execution space type?

[brian-kelley]

@lucbv Hmm, you might be right about that. Maybe for some type T, T& or const T& is the argument type but an enable_if only matches a T?

Anyway, the spmv unit tests do actually test this exact call with all template arguments deduced, so something else is going on.

[e10harvey]

Hm. I would expect the template arg to be inferrable from instances[i], where std::vector<exec_space> instances;.

[brian-kelley]

@e10harvey I just tried a spmv call similar to what you had (where the space is an element of a std::vector) but it compiled without errors. Could you post the error message you got?

[e10harvey]

From the source branch in #1963:

$ git rev-parse HEAD
35d8ff92b320c27fb36ce2875187db6d3ef49c92
$ git diff
diff --git a/perf_test/sparse/KokkosSparse_gs.cpp b/perf_test/sparse/KokkosSparse_gs.cpp
index 163fdb2dd..b32940c6c 100644
--- a/perf_test/sparse/KokkosSparse_gs.cpp
+++ b/perf_test/sparse/KokkosSparse_gs.cpp
@@ -326,7 +326,7 @@ void runGS(const GS_Parameters& params) {
     double bnorm   = KokkosBlas::nrm2(instances[i], b[i]);
     scalar_t alpha = Kokkos::reduction_identity<scalar_t>::prod();
     scalar_t beta  = -alpha;
-    KokkosSparse::spmv<exec_space, scalar_t, crsMat_t, scalar_view_t, scalar_t,
+    KokkosSparse::spmv<scalar_t, crsMat_t, scalar_view_t, scalar_t,
                        scalar_view_t>(instances[i], "N", alpha, blk_A, x[i],
                                       beta, res);
     double resnorm = KokkosBlas::nrm2(instances[i], res);
$ make sparse_gs
build] [ 98%] Built target kokkoskernels
[build] [100%] Building CXX object perf_test/sparse/CMakeFiles/sparse_gs.dir/KokkosSparse_gs.cpp.o
[build] /path/to/perf_test/sparse/KokkosSparse_gs.cpp:329:5: error: no matching function for call to 'spmv'
[build]     KokkosSparse::spmv<scalar_t, crsMat_t, scalar_view_t, scalar_t,
[build]     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[build] /path/to/perf_test/sparse/KokkosSparse_gs.cpp:477:5: note: in instantiation of function template specialization 'runGS<Kokkos::Serial>' requested here
[build]     runGS<Kokkos::DefaultExecutionSpace>(params);
[build]     ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1186:6: note: candidate function template not viable: no known conversion from 'value_type' (aka 'Kokkos::Serial') to 'KokkosKernels::Experimental::Controls' for 1st argument
[build] void spmv(KokkosKernels::Experimental::Controls controls, const char mode[],
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1288:6: note: candidate function template not viable: no known conversion from 'value_type' (aka 'Kokkos::Serial') to 'const scalar_t' (aka 'const double') for 1st argument
[build] void spmv(const ExecutionSpace& space, const char mode[],
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1205:6: note: candidate template ignored: requirement '!KokkosSparse::is_crs_matrix<KokkosSparse::CrsMatrix<double, int, Kokkos::Serial, void, unsigned long>>::value' was not satisfied [with AlphaType = scalar_t, AMatrix = crsMat_t, XVector = scalar_view_t, BetaType = scalar_t, YVector = scalar_view_t]
[build] void spmv(KokkosKernels::Experimental::Controls /*controls*/,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1259:6: note: candidate function template not viable: requires 6 arguments, but 7 were provided
[build] void spmv(const char mode[], const AlphaType& alpha, const AMatrix& A,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:263:6: note: candidate function template not viable: requires 8 arguments, but 7 were provided
[build] void spmv(KokkosKernels::Experimental::Controls controls, const char mode[],
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:458:6: note: candidate function template not viable: requires 8 arguments, but 7 were provided
[build] void spmv(KokkosKernels::Experimental::Controls controls, const char mode[],
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:814:6: note: candidate function template not viable: requires 8 arguments, but 7 were provided
[build] void spmv(KokkosKernels::Experimental::Controls controls, const char mode[],
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1008:6: note: candidate function template not viable: requires 8 arguments, but 7 were provided
[build] void spmv(KokkosKernels::Experimental::Controls controls, const char mode[],
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1064:6: note: candidate function template not viable: requires 8 arguments, but 7 were provided
[build] void spmv(const ExecutionSpace& space,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:1227:6: note: candidate function template not viable: requires 8 arguments, but 7 were provided
[build] void spmv(const ExecutionSpace& /* space */,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:76:6: note: candidate function template not viable: requires 9 arguments, but 7 were provided
[build] void spmv(const ExecutionSpace& space,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:275:6: note: candidate function template not viable: requires 9 arguments, but 7 were provided
[build] void spmv(const ExecutionSpace& space,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:653:6: note: candidate function template not viable: requires 9 arguments, but 7 were provided
[build] void spmv(const ExecutionSpace& space,
[build]      ^
[build] /path/to/sparse/src/KokkosSparse_spmv.hpp:826:6: note: candidate function template not viable: requires 9 arguments, but 7 were provided
[build] void spmv(const ExecutionSpace& space,
[build]      ^
[build] 1 error generated.
[build] make[3]: *** [perf_test/sparse/CMakeFiles/sparse_gs.dir/KokkosSparse_gs.cpp.o] Error 1
[build] make[2]: *** [perf_test/sparse/CMakeFiles/sparse_gs.dir/all] Error 2
[build] make[1]: *** [perf_test/sparse/CMakeFiles/sparse_gs.dir/rule] Error 2
[build] make: *** [sparse_gs] Error 2

Not specifying any template argument does work though.

It looks like you must specify template arguments from left to right rather than right to left.

[brian-kelley]

Oh yeah, I was thinking that not specifying any arguments should work, and is generally how I would expect spmv to be used.

[e10harvey]

There should be a 'Easy close' and 'Almost impossible close' button next to 'close with comment' ; )