make/cmake: remove openmp option: OpenMP is required

CMakeLists.txt

@@ -53,7 +53,6 @@ endif()
 option( BUILD_SHARED_LIBS "Build shared libraries" true )
 option( build_tests "Build test suite" "${slate_is_project}" )
 option( color "Use ANSI color output" true )
-option( use_openmp "Use OpenMP, if available" true )
 option( c_api "Build C API" false )
 # todo: option( fortran_api "Build Fortran API. Requires C API." false )
 
@@ -121,7 +120,6 @@ BUILD_SHARED_LIBS      = ${BUILD_SHARED_LIBS}
 build_tests            = ${build_tests}
 color                  = ${color}
 gpu_backend            = ${gpu_backend}
-use_openmp             = ${use_openmp}
 c_api                  = ${c_api}
 fortran_api            = ${fortran_api}
 slate_is_project       = ${slate_is_project}
@@ -300,23 +298,13 @@ endif()
 # OpenMP support.
 # Needed before BLAS++.
 message( "" )
-message( "---------------------------------------- OpenMP: use_openmp = ${use_openmp}" )
-set( slate_use_openmp false )  # output in slateConfig.cmake.in
-if (NOT use_openmp)
-    message( STATUS "User has requested to NOT use OpenMP" )
+message( "---------------------------------------- OpenMP" )
+find_package( OpenMP )
+if (OpenMP_CXX_FOUND)
+    target_link_libraries( slate PUBLIC "OpenMP::OpenMP_CXX" )
+    set( slate_use_openmp true )  # historical; output in slateConfig.cmake.in
 else()
-    find_package( OpenMP )
-    if (OpenMP_CXX_FOUND)
-        target_link_libraries( slate PUBLIC "OpenMP::OpenMP_CXX" )
-        set( slate_use_openmp true )
-    else()
-        message( STATUS "No OpenMP support in SLATE" )
-        target_sources(
-            slate
-            PRIVATE
-            src/stubs/openmp_stubs.cc
-        )
-    endif()
+    message( FATAL_ERROR "OpenMP is required" )
 endif()
 
 #-------------------------------------------------------------------------------

GNUmakefile

@@ -220,7 +220,7 @@ ifeq (${openmp},1)
         LDFLAGS  += -fopenmp
     endif
 else
-    slate_src += src/stubs/openmp_stubs.cc
+    ${error ERROR: unsupported `openmp=${openmp}`. OpenMP is required.}
 endif
 
 #-------------------------------------------------------------------------------

INSTALL.md

@@ -30,7 +30,8 @@ which includes BLAS++ and LAPACK++.
 
 Configure and compile the SLATE library and its tester,
 then install the headers and library. This will also compile
-BLAS++, LAPACK++, and TestSweeper.
+BLAS++, LAPACK++, and TestSweeper. SLATE requires MPI and an
+OpenMP C++17 compiler.
 
 **Option 1: Makefile**
 
@@ -243,10 +244,6 @@ options include:
         or other valid HIP architecture, separated by space.
         See https://llvm.org/docs/AMDGPUUsage.html
 
-    openmp
-        SLATE will compile with OpenMP by default. To compile without
-        OpenMP, set `openmp = 0`.
-
     c_api
         Whether to build C API. Python is required. One of:
         1                   build C API
@@ -320,11 +317,6 @@ options include:
         For example, `-DCMAKE_CUDA_ARCHITECTURES=70` should be added for
         the Volta architecture.
 
-    use_openmp
-        Whether to use OpenMP, if available. One of:
-        yes (default)
-        no
-
     build_tests
         Whether to build test suite (test/tester).
         Requires ScaLAPACK unless SCALAPACK_LIBRARIES=none. One of:

include/slate/internal/openmp.hh

@@ -3,9 +3,6 @@
 // This program is free software: you can redistribute it and/or modify it under
 // the terms of the BSD 3-Clause license. See the accompanying LICENSE file.
 
-//------------------------------------------------------------------------------
-/// @file
-///
 #ifndef SLATE_OPENMP_HH
 #define SLATE_OPENMP_HH