From 468d0026f0b115715114116634fa88e31f48e8ed Mon Sep 17 00:00:00 2001
From: Thomas Gibson <14180421+thomasgibson@users.noreply.github.com>
Date: Mon, 17 Oct 2022 22:04:42 -0700
Subject: [PATCH] Allow for manually specifying MPI flags

---
 CMakeLists.txt | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8e599e7a..88f73df1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,7 +6,6 @@ project(BabelStream VERSION 4.0 LANGUAGES CXX)
 # set(CMAKE_VERBOSE_MAKEFILE ON)
 
 option(WITH_MPI "Enable MPI" OFF)
-find_package(MPI)
 
 # some nicer defaults for standard C++
 set(CMAKE_CXX_EXTENSIONS OFF)
@@ -70,6 +69,10 @@ hint_flag(CXX_EXTRA_LIBRARIES "
         Use this for linking extra libraries (e.g `-lmylib`, or simply `mylib`)")
 hint_flag(CXX_EXTRA_LINKER_FLAGS "
         Append to linker flags (i.e GCC's `-Wl` or equivalent)")
+hint_flag(MPI_CXX_FLAGS "
+	Append MPI flags to common compile flags.")
+hint_flag(MPI_CXX_LINKER_FLAGS "
+	Append linking flags specific to MPI.")
 
 # Honor user's CXX_EXTRA_LINK_FLAGS
 set(CXX_EXTRA_LINK_FLAGS ${CXX_EXTRA_FLAGS} ${CXX_EXTRA_LINK_FLAGS})
@@ -143,10 +146,12 @@ message(STATUS "CXX Flags   : ${CMAKE_CXX_FLAGS_${BUILD_TYPE}} ${ACTUAL_${BUILD_
         Default                  = `${DEFAULT_${BUILD_TYPE}_FLAGS}`
         Override (RELEASE_FLAGS) = `${${BUILD_TYPE}_FLAGS}`
         Extras (CXX_EXTRA_FLAGS) = `${CXX_EXTRA_FLAGS}`")
-message(STATUS "Link Flags  : ${LINK_FLAGS} ${CXX_EXTRA_LINK_FLAGS}")
-message(STATUS "Linker Flags: ${CMAKE_EXE_LINKER_FLAGS} ${CXX_EXTRA_LINKER_FLAGS} ")
-message(STATUS "Defs        : ${IMPL_DEFINITIONS}")
-message(STATUS "Executable  : ${EXE_NAME}")
+message(STATUS "MPI CXX Flags  : ${MPI_CXX_FLAGS}")
+message(STATUS "Link Flags     : ${LINK_FLAGS} ${CXX_EXTRA_LINK_FLAGS}")
+message(STATUS "MPI Link Flags : ${MPI_CXX_LINKER_FLAGS}")
+message(STATUS "Linker Flags   : ${CMAKE_EXE_LINKER_FLAGS} ${CXX_EXTRA_LINKER_FLAGS} ")
+message(STATUS "Defs           : ${IMPL_DEFINITIONS}")
+message(STATUS "Executable     : ${EXE_NAME}")
 
 # below we have all the usual CMake target setup steps
 
@@ -167,12 +172,17 @@ target_link_options(${EXE_NAME} PUBLIC ${LINK_FLAGS} ${CXX_EXTRA_LINK_FLAGS})
 
 # If MPI is requested, link relevant libraries
 if (WITH_MPI)
+    add_definitions(-DUSE_MPI)
+    find_package(MPI)
     if (MPI_FOUND)
         message(STATUS "MPI requested and found. Linking relevant MPI libraries.")
         target_link_libraries(${EXE_NAME} PUBLIC MPI::MPI_CXX)
-        add_definitions(-DUSE_MPI)
+    elseif (MPI_CXX_FLAGS OR MPI_CXX_LINKER_FLAGS)
+        message(STATUS "MPI requested. Using provided MPI_CXX_FLAGS and MPI_CXX_LINKER_FLAGS.")
+        target_compile_options(${EXE_NAME} PUBLIC ${MPI_CXX_FLAGS})
+        target_link_libraries(${EXE_NAME} PUBLIC ${MPI_CXX_LINKER_FLAGS})
     else ()
-        message(FATAL_ERROR "MPI requested, but no implementation has been detected.")
+        message(FATAL_ERROR "MPI requested, but no implementation has been detected. Please specify MPI_CXX_FLAGS and MPI_CXX_LINKER_FLAGS.")
     endif ()
 endif ()