summaryrefslogtreecommitdiffstats
path: root/Modules/FindMPI.cmake
blob: 143d10af068697e9edb7604c848f6f50571ef99c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
# - Find a Message Passing Interface (MPI) implementation
# The Message Passing Interface (MPI) is a library used to write
# high-performance distributed-memory parallel applications, and
# is typically deployed on a cluster. MPI is a standard interface
# (defined by the MPI forum) for which many implementations are
# available. All of them have somewhat different include paths,
# libraries to link against, etc., and this module tries to smooth
# out those differences.
#
# === Variables ===
#
# This module will set the following variables per language in your project,
# where <lang> is one of C, CXX, or Fortran:
#   MPI_<lang>_FOUND           TRUE if FindMPI found MPI flags for <lang>
#   MPI_<lang>_COMPILER        MPI Compiler wrapper for <lang>
#   MPI_<lang>_COMPILE_FLAGS   Compilation flags for MPI programs
#   MPI_<lang>_INCLUDE_PATH    Include path(s) for MPI header
#   MPI_<lang>_LINK_FLAGS      Linking flags for MPI programs
#   MPI_<lang>_LIBRARIES       All libraries to link MPI programs against
# Additionally, FindMPI sets the following variables for running MPI
# programs from the command line:
#   MPIEXEC                    Executable for running MPI programs
#   MPIEXEC_NUMPROC_FLAG       Flag to pass to MPIEXEC before giving
#                              it the number of processors to run on
#   MPIEXEC_PREFLAGS           Flags to pass to MPIEXEC directly
#                              before the executable to run.
#   MPIEXEC_POSTFLAGS          Flags to pass to MPIEXEC after other flags
# === Usage ===
#
# To use this module, simply call FindMPI from a CMakeLists.txt file, or
# run find_package(MPI), then run CMake.  If you are happy with the auto-
# detected configuration for your language, then you're done.  If not, you
# have two options:
#   1. Set MPI_<lang>_COMPILER to the MPI wrapper (mpicc, etc.) of your
#      choice and reconfigure.  FindMPI will attempt to determine all the
#      necessary variables using THAT compiler's compile and link flags.
#   2. If this fails, or if your MPI implementation does not come with
#      a compiler wrapper, then set both MPI_<lang>_LIBRARIES and
#      MPI_<lang>_INCLUDE_PATH.  You may also set any other variables
#      listed above, but these two are required.  This will circumvent
#      autodetection entirely.
# When configuration is successful, MPI_<lang>_COMPILER will be set to the
# compiler wrapper for <lang>, if it was found.  MPI_<lang>_FOUND and other
# variables above will be set if any MPI implementation was found for <lang>,
# regardless of whether a compiler was found.
#
# When using MPIEXEC to execute MPI applications, you should typically use
# all of the MPIEXEC flags as follows:
#   ${MPIEXEC} ${MPIEXEC_NUMPROC_FLAG} PROCS
#     ${MPIEXEC_PREFLAGS} EXECUTABLE ${MPIEXEC_POSTFLAGS} ARGS
# where PROCS is the number of processors on which to execute the program,
# EXECUTABLE is the MPI program, and ARGS are the arguments to pass to the
# MPI program.
#
# === Backward Compatibility ===
#
# For backward compatibility with older versions of FindMPI, these
# variables are set, but deprecated:
#   MPI_FOUND           MPI_COMPILER        MPI_LIBRARY
#   MPI_COMPILE_FLAGS   MPI_INCLUDE_PATH    MPI_EXTRA_LIBRARY
#   MPI_LINK_FLAGS      MPI_LIBRARIES
# In new projects, please use the MPI_<lang>_XXX equivalents.

#=============================================================================
# Copyright 2001-2011 Kitware, Inc.
# Copyright 2010-2011 Todd Gamblin tgamblin@llnl.gov
# Copyright 2001-2009 Dave Partyka
#
# Distributed under the OSI-approved BSD License (the "License");
# see accompanying file Copyright.txt for details.
#
# This software is distributed WITHOUT ANY WARRANTY; without even the
# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the License for more information.
#=============================================================================
# (To distribute this file outside of CMake, substitute the full
#  License text for the above reference.)

# include this to handle the QUIETLY and REQUIRED arguments
include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
include(${CMAKE_CURRENT_LIST_DIR}/GetPrerequisites.cmake)

#
# This part detects MPI compilers, attempting to wade through the mess of compiler names in
# a sensible way.
#
# The compilers are detected in this order:
#
# 1. Try to find the most generic availble MPI compiler, as this is usually set up by
#    cluster admins.  e.g., if plain old mpicc is available, we'll use it and assume it's
#    the right compiler.
#
# 2. If a generic mpicc is NOT found, then we attempt to find one that matches
#    CMAKE_<lang>_COMPILER_ID. e.g. if you are using XL compilers, we'll try to find mpixlc
#    and company, but not mpiicc.  This hopefully prevents toolchain mismatches.
#
# If you want to force a particular MPI compiler other than what we autodetect (e.g. if you
# want to compile regular stuff with GNU and parallel stuff with Intel), you can always set
# your favorite MPI_<lang>_COMPILER explicitly and this stuff will be ignored.
#

# Start out with the generic MPI compiler names, as these are most commonly used.
set(_MPI_C_COMPILER_NAMES                  mpicc    mpcc      mpicc_r mpcc_r)
set(_MPI_CXX_COMPILER_NAMES                mpicxx   mpiCC     mpcxx   mpCC    mpic++   mpc++
                                           mpicxx_r mpiCC_r   mpcxx_r mpCC_r  mpic++_r mpc++_r)
set(_MPI_Fortran_COMPILER_NAMES            mpif95   mpif95_r  mpf95   mpf95_r
                                           mpif90   mpif90_r  mpf90   mpf90_r
                                           mpif77   mpif77_r  mpf77   mpf77_r)

# GNU compiler names
set(_MPI_GNU_C_COMPILER_NAMES              mpigcc mpgcc mpigcc_r mpgcc_r)
set(_MPI_GNU_CXX_COMPILER_NAMES            mpig++ mpg++ mpig++_r mpg++_r)
set(_MPI_GNU_Fortran_COMPILER_NAMES        mpigfortran mpgfortran mpigfortran_r mpgfortran_r
                                           mpig77 mpig77_r mpg77 mpg77_r)

# Intel MPI compiler names
set(_MPI_Intel_C_COMPILER_NAMES            mpiicc)
set(_MPI_Intel_CXX_COMPILER_NAMES          mpiicpc  mpiicxx mpiic++ mpiiCC)
set(_MPI_Intel_Fortran_COMPILER_NAMES      mpiifort mpiif95 mpiif90 mpiif77)

# PGI compiler names
set(_MPI_PGI_C_COMPILER_NAMES              mpipgcc mppgcc)
set(_MPI_PGI_CXX_COMPILER_NAMES            mpipgCC mppgCC)
set(_MPI_PGI_Fortran_COMPILER_NAMES        mpipgf95 mpipgf90 mppgf95 mppgf90 mpipgf77 mppgf77)

# XLC MPI Compiler names
set(_MPI_XL_C_COMPILER_NAMES               mpxlc      mpxlc_r    mpixlc     mpixlc_r)
set(_MPI_XL_CXX_COMPILER_NAMES             mpixlcxx   mpixlC     mpixlc++   mpxlcxx   mpxlc++   mpixlc++   mpxlCC
                                           mpixlcxx_r mpixlC_r   mpixlc++_r mpxlcxx_r mpxlc++_r mpixlc++_r mpxlCC_r)
set(_MPI_XL_Fortran_COMPILER_NAMES         mpixlf95   mpixlf95_r mpxlf95 mpxlf95_r
                                           mpixlf90   mpixlf90_r mpxlf90 mpxlf90_r
                                           mpixlf77   mpixlf77_r mpxlf77 mpxlf77_r
                                           mpixlf     mpixlf_r   mpxlf   mpxlf_r)

# append vendor-specific compilers to the list if we either don't know the compiler id,
# or if we know it matches the regular compiler.
foreach (lang C CXX Fortran)
  foreach (id GNU Intel PGI XL)
    if (NOT CMAKE_${lang}_COMPILER_ID OR "${CMAKE_${lang}_COMPILER_ID}" STREQUAL "${id}")
      list(APPEND _MPI_${lang}_COMPILER_NAMES ${_MPI_${id}_${lang}_COMPILER_NAMES})
    endif()
    unset(_MPI_${id}_${lang}_COMPILER_NAMES)    # clean up the namespace here
  endforeach()
endforeach()


# Names to try for MPI exec
set(_MPI_EXEC_NAMES                        mpiexec mpirun lamexec srun)

# Grab the path to MPI from the registry if we're on windows.
set(_MPI_PREFIX_PATH)
if(WIN32)
  list(APPEND _MPI_PREFIX_PATH "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MPICH\\SMPD;binary]/..")
  list(APPEND _MPI_PREFIX_PATH "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MPICH2;Path]")
  list(APPEND _MPI_PREFIX_PATH "$ENV{ProgramW6432}/MPICH2/")
endif()

# Build a list of prefixes to search for MPI.
foreach(SystemPrefixDir ${CMAKE_SYSTEM_PREFIX_PATH})
  foreach(MpiPackageDir ${_MPI_PREFIX_PATH})
    if(EXISTS ${SystemPrefixDir}/${MpiPackageDir})
      list(APPEND _MPI_PREFIX_PATH "${SystemPrefixDir}/${MpiPackageDir}")
    endif()
  endforeach()
endforeach()


#
# interrogate_mpi_compiler(lang try_libs)
#
# Attempts to extract compiler and linker args from an MPI compiler. The arguments set
# by this function are:
#
#   MPI_<lang>_INCLUDE_PATH    MPI_<lang>_LINK_FLAGS     MPI_<lang>_FOUND
#   MPI_<lang>_COMPILE_FLAGS   MPI_<lang>_LIBRARIES
#
# MPI_<lang>_COMPILER must be set beforehand to the absolute path to an MPI compiler for
# <lang>.  Additionally, MPI_<lang>_INCLUDE_PATH and MPI_<lang>_LIBRARIES may be set
# to skip autodetection.
#
# If try_libs is TRUE, this will also attempt to find plain MPI libraries in the usual
# way.  In general, this is not as effective as interrogating the compilers, as it
# ignores language-specific flags and libraries.  However, some MPI implementations
# (Windows implementations) do not have compiler wrappers, so this approach must be used.
#
function (interrogate_mpi_compiler lang try_libs)
  # MPI_${lang}_NO_INTERROGATE will be set to a compiler name when the *regular* compiler was
  # discovered to be the MPI compiler.  This happens on machines like the Cray XE6 that use
  # modules to set cc, CC, and ftn to the MPI compilers.  If the user force-sets another MPI
  # compiler, MPI_${lang}_COMPILER won't be equal to MPI_${lang}_NO_INTERROGATE, and we'll
  # inspect that compiler anew.  This allows users to set new compilers w/o rm'ing cache.
  string(COMPARE NOTEQUAL "${MPI_${lang}_NO_INTERROGATE}" "${MPI_${lang}_COMPILER}" interrogate)

  # If MPI is set already in the cache, don't bother with interrogating the compiler.
  if (interrogate AND ((NOT MPI_${lang}_INCLUDE_PATH) OR (NOT MPI_${lang}_LIBRARIES)))
    if (MPI_${lang}_COMPILER)
      # Check whether the -showme:compile option works. This indicates that we have either OpenMPI
      # or a newer version of LAM-MPI, and implies that -showme:link will also work.
      execute_process(
        COMMAND ${MPI_${lang}_COMPILER} -showme:compile
        OUTPUT_VARIABLE  MPI_COMPILE_CMDLINE OUTPUT_STRIP_TRAILING_WHITESPACE
        ERROR_VARIABLE   MPI_COMPILE_CMDLINE ERROR_STRIP_TRAILING_WHITESPACE
        RESULT_VARIABLE  MPI_COMPILER_RETURN)

      if (MPI_COMPILER_RETURN EQUAL 0)
        # If we appear to have -showme:compile, then we should
        # also have -showme:link. Try it.
        execute_process(
          COMMAND ${MPI_${lang}_COMPILER} -showme:link
          OUTPUT_VARIABLE  MPI_LINK_CMDLINE OUTPUT_STRIP_TRAILING_WHITESPACE
          ERROR_VARIABLE   MPI_LINK_CMDLINE ERROR_STRIP_TRAILING_WHITESPACE
          RESULT_VARIABLE  MPI_COMPILER_RETURN)

        if (MPI_COMPILER_RETURN EQUAL 0)
          # We probably have -showme:incdirs and -showme:libdirs as well,
          # so grab that while we're at it.
          execute_process(
            COMMAND ${MPI_${lang}_COMPILER} -showme:incdirs
            OUTPUT_VARIABLE  MPI_INCDIRS OUTPUT_STRIP_TRAILING_WHITESPACE
            ERROR_VARIABLE   MPI_INCDIRS ERROR_STRIP_TRAILING_WHITESPACE)

          execute_process(
            COMMAND ${MPI_${lang}_COMPILER} -showme:libdirs
            OUTPUT_VARIABLE  MPI_LIBDIRS OUTPUT_STRIP_TRAILING_WHITESPACE
            ERROR_VARIABLE   MPI_LIBDIRS ERROR_STRIP_TRAILING_WHITESPACE)

        else()
          # reset things here if something went wrong.
          set(MPI_COMPILE_CMDLINE)
          set(MPI_LINK_CMDLINE)
        endif()
      endif ()

      # Older versions of LAM-MPI have "-showme". Try to find that.
      if (NOT MPI_COMPILER_RETURN EQUAL 0)
        execute_process(
          COMMAND ${MPI_${lang}_COMPILER} -showme
          OUTPUT_VARIABLE  MPI_COMPILE_CMDLINE OUTPUT_STRIP_TRAILING_WHITESPACE
          ERROR_VARIABLE   MPI_COMPILE_CMDLINE ERROR_STRIP_TRAILING_WHITESPACE
          RESULT_VARIABLE  MPI_COMPILER_RETURN)
      endif()

      # MVAPICH uses -compile-info and -link-info.  Try them.
      if (NOT MPI_COMPILER_RETURN EQUAL 0)
        execute_process(
          COMMAND ${MPI_${lang}_COMPILER} -compile-info
          OUTPUT_VARIABLE  MPI_COMPILE_CMDLINE OUTPUT_STRIP_TRAILING_WHITESPACE
          ERROR_VARIABLE   MPI_COMPILE_CMDLINE ERROR_STRIP_TRAILING_WHITESPACE
          RESULT_VARIABLE  MPI_COMPILER_RETURN)

        # If we have compile-info, also have link-info.
        if (MPI_COMPILER_RETURN EQUAL 0)
          execute_process(
            COMMAND ${MPI_${lang}_COMPILER} -link-info
            OUTPUT_VARIABLE  MPI_LINK_CMDLINE OUTPUT_STRIP_TRAILING_WHITESPACE
            ERROR_VARIABLE   MPI_LINK_CMDLINE ERROR_STRIP_TRAILING_WHITESPACE
            RESULT_VARIABLE  MPI_COMPILER_RETURN)
        endif()

        # make sure we got compile and link.  Reset vars if something's wrong.
        if (NOT MPI_COMPILER_RETURN EQUAL 0)
          set(MPI_COMPILE_CMDLINE)
          set(MPI_LINK_CMDLINE)
        endif()
      endif()

      # MPICH just uses "-show". Try it.
      if (NOT MPI_COMPILER_RETURN EQUAL 0)
        execute_process(
          COMMAND ${MPI_${lang}_COMPILER} -show
          OUTPUT_VARIABLE  MPI_COMPILE_CMDLINE OUTPUT_STRIP_TRAILING_WHITESPACE
          ERROR_VARIABLE   MPI_COMPILE_CMDLINE ERROR_STRIP_TRAILING_WHITESPACE
          RESULT_VARIABLE  MPI_COMPILER_RETURN)
      endif()

      if (MPI_COMPILER_RETURN EQUAL 0)
        # We have our command lines, but we might need to copy MPI_COMPILE_CMDLINE
        # into MPI_LINK_CMDLINE, if we didn't find the link line.
        if (NOT MPI_LINK_CMDLINE)
          set(MPI_LINK_CMDLINE ${MPI_COMPILE_CMDLINE})
        endif()
      else()
        message(STATUS "Unable to determine MPI from MPI driver ${MPI_${lang}_COMPILER}")
        set(MPI_COMPILE_CMDLINE)
        set(MPI_LINK_CMDLINE)
      endif()

      # Here, we're done with the interrogation part, and we'll try to extract args we care
      # about from what we learned from the compiler wrapper scripts.

      # If interrogation came back with something, extract our variable from the MPI command line
      if (MPI_COMPILE_CMDLINE OR MPI_LINK_CMDLINE)
        # Extract compile flags from the compile command line.
        string(REGEX MATCHALL "(^| )-[Df]([^\" ]+|\"[^\"]+\")" MPI_ALL_COMPILE_FLAGS "${MPI_COMPILE_CMDLINE}")
        set(MPI_COMPILE_FLAGS_WORK)

        foreach(FLAG ${MPI_ALL_COMPILE_FLAGS})
          if (MPI_COMPILE_FLAGS_WORK)
            set(MPI_COMPILE_FLAGS_WORK "${MPI_COMPILE_FLAGS_WORK} ${FLAG}")
          else()
            set(MPI_COMPILE_FLAGS_WORK ${FLAG})
          endif()
        endforeach()

        # Extract include paths from compile command line
        string(REGEX MATCHALL "(^| )-I([^\" ]+|\"[^\"]+\")" MPI_ALL_INCLUDE_PATHS "${MPI_COMPILE_CMDLINE}")
        foreach(IPATH ${MPI_ALL_INCLUDE_PATHS})
          string(REGEX REPLACE "^ ?-I" "" IPATH ${IPATH})
          string(REGEX REPLACE "//" "/" IPATH ${IPATH})
          list(APPEND MPI_INCLUDE_PATH_WORK ${IPATH})
        endforeach()

        # try using showme:incdirs if extracting didn't work.
        if (NOT MPI_INCLUDE_PATH_WORK)
          set(MPI_INCLUDE_PATH_WORK ${MPI_INCDIRS})
          separate_arguments(MPI_INCLUDE_PATH_WORK)
        endif()

        # If all else fails, just search for mpi.h in the normal include paths.
        if (NOT MPI_INCLUDE_PATH_WORK)
          set(MPI_HEADER_PATH "MPI_HEADER_PATH-NOTFOUND" CACHE FILEPATH "Cleared" FORCE)
          find_path(MPI_HEADER_PATH mpi.h
            HINTS ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
            PATH_SUFFIXES include)
          set(MPI_INCLUDE_PATH_WORK ${MPI_HEADER_PATH})
        endif()

        # Extract linker paths from the link command line
        string(REGEX MATCHALL "(^| |-Wl,)-L([^\" ]+|\"[^\"]+\")" MPI_ALL_LINK_PATHS "${MPI_LINK_CMDLINE}")
        set(MPI_LINK_PATH)
        foreach(LPATH ${MPI_ALL_LINK_PATHS})
          string(REGEX REPLACE "^(| |-Wl,)-L" "" LPATH ${LPATH})
          string(REGEX REPLACE "//" "/" LPATH ${LPATH})
          list(APPEND MPI_LINK_PATH ${LPATH})
        endforeach()

        # try using showme:libdirs if extracting didn't work.
        if (NOT MPI_LINK_PATH)
          set(MPI_LINK_PATH ${MPI_LIBDIRS})
          separate_arguments(MPI_LINK_PATH)
        endif()

        # Extract linker flags from the link command line
        string(REGEX MATCHALL "(^| )-Wl,([^\" ]+|\"[^\"]+\")" MPI_ALL_LINK_FLAGS "${MPI_LINK_CMDLINE}")
        set(MPI_LINK_FLAGS_WORK)
        foreach(FLAG ${MPI_ALL_LINK_FLAGS})
          if (MPI_LINK_FLAGS_WORK)
            set(MPI_LINK_FLAGS_WORK "${MPI_LINK_FLAGS_WORK} ${FLAG}")
          else()
            set(MPI_LINK_FLAGS_WORK ${FLAG})
          endif()
        endforeach()

        # Extract the set of libraries to link against from the link command
        # line
        string(REGEX MATCHALL "(^| )-l([^\" ]+|\"[^\"]+\")" MPI_LIBNAMES "${MPI_LINK_CMDLINE}")
        # add the compiler implicit directories because some compilers
        # such as the intel compiler have libraries that show up
        # in the showme list that can only be found in the implicit
        # link directories of the compiler. Do this for C++ and C
        # compilers if the implicit link directories are defined.
        if (DEFINED CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES)
          set(MPI_LINK_PATH
            "${MPI_LINK_PATH};${CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES}")
        endif ()

        if (DEFINED CMAKE_C_IMPLICIT_LINK_DIRECTORIES)
          set(MPI_LINK_PATH
            "${MPI_LINK_PATH};${CMAKE_C_IMPLICIT_LINK_DIRECTORIES}")
        endif ()

        # Determine full path names for all of the libraries that one needs
        # to link against in an MPI program
        foreach(LIB ${MPI_LIBNAMES})
          string(REGEX REPLACE "^ ?-l" "" LIB ${LIB})
          # MPI_LIB is cached by find_library, but we don't want that.  Clear it first.
          set(MPI_LIB "MPI_LIB-NOTFOUND" CACHE FILEPATH "Cleared" FORCE)
          find_library(MPI_LIB NAMES ${LIB} HINTS ${MPI_LINK_PATH})

          if (MPI_LIB)
            list(APPEND MPI_LIBRARIES_WORK ${MPI_LIB})
          elseif (NOT MPI_FIND_QUIETLY)
            message(WARNING "Unable to find MPI library ${LIB}")
          endif()
        endforeach()

        # Sanity check MPI_LIBRARIES to make sure there are enough libraries
        list(LENGTH MPI_LIBRARIES_WORK MPI_NUMLIBS)
        list(LENGTH MPI_LIBNAMES MPI_NUMLIBS_EXPECTED)
        if (NOT MPI_NUMLIBS EQUAL MPI_NUMLIBS_EXPECTED)
          set(MPI_LIBRARIES_WORK "MPI_${lang}_LIBRARIES-NOTFOUND")
        endif()
      endif()

    elseif(try_libs)
      # If we didn't have an MPI compiler script to interrogate, attempt to find everything
      # with plain old find functions.  This is nasty because MPI implementations have LOTS of
      # different library names, so this section isn't going to be very generic.  We need to
      # make sure it works for MS MPI, though, since there are no compiler wrappers for that.
      find_path(MPI_HEADER_PATH mpi.h
        HINTS ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
        PATH_SUFFIXES include Inc)
      set(MPI_INCLUDE_PATH_WORK ${MPI_HEADER_PATH})

      # Decide between 32-bit and 64-bit libraries for Microsoft's MPI
      if("${CMAKE_SIZEOF_VOID_P}" EQUAL 8)
        set(MS_MPI_ARCH_DIR amd64)
      else()
        set(MS_MPI_ARCH_DIR i386)
      endif()

      set(MPI_LIB "MPI_LIB-NOTFOUND" CACHE FILEPATH "Cleared" FORCE)
      find_library(MPI_LIB
        NAMES         mpi mpich mpich2 msmpi
        HINTS         ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
        PATH_SUFFIXES lib lib/${MS_MPI_ARCH_DIR} Lib Lib/${MS_MPI_ARCH_DIR})
      set(MPI_LIBRARIES_WORK ${MPI_LIB})

      # Right now, we only know about the extra libs for C++.
      # We could add Fortran here (as there is usually libfmpich, etc.), but
      # this really only has to work with MS MPI on Windows.
      # Assume that other MPI's are covered by the compiler wrappers.
      if (${lang} STREQUAL CXX)
        set(MPI_LIB "MPI_LIB-NOTFOUND" CACHE FILEPATH "Cleared" FORCE)
        find_library(MPI_LIB
          NAMES         mpi++ mpicxx cxx mpi_cxx
          HINTS         ${_MPI_BASE_DIR} ${_MPI_PREFIX_PATH}
          PATH_SUFFIXES lib)
        if (MPI_LIBRARIES_WORK AND MPI_LIB)
          list(APPEND MPI_LIBRARIES_WORK ${MPI_LIB})
        endif()
      endif()

      if (NOT MPI_LIBRARIES_WORK)
        set(MPI_LIBRARIES_WORK "MPI_${lang}_LIBRARIES-NOTFOUND")
      endif()
    endif()

    # If we found MPI, set up all of the appropriate cache entries
    set(MPI_${lang}_COMPILE_FLAGS ${MPI_COMPILE_FLAGS_WORK} CACHE STRING "MPI ${lang} compilation flags"         FORCE)
    set(MPI_${lang}_INCLUDE_PATH  ${MPI_INCLUDE_PATH_WORK}  CACHE STRING "MPI ${lang} include path"              FORCE)
    set(MPI_${lang}_LINK_FLAGS    ${MPI_LINK_FLAGS_WORK}    CACHE STRING "MPI ${lang} linking flags"             FORCE)
    set(MPI_${lang}_LIBRARIES     ${MPI_LIBRARIES_WORK}     CACHE STRING "MPI ${lang} libraries to link against" FORCE)
    mark_as_advanced(MPI_${lang}_COMPILE_FLAGS MPI_${lang}_INCLUDE_PATH MPI_${lang}_LINK_FLAGS MPI_${lang}_LIBRARIES)

    # clear out our temporary lib/header detectionv variable here.
    set(MPI_LIB         "MPI_LIB-NOTFOUND"         CACHE INTERNAL "Scratch variable for MPI lib detection"    FORCE)
    set(MPI_HEADER_PATH "MPI_HEADER_PATH-NOTFOUND" CACHE INTERNAL "Scratch variable for MPI header detection" FORCE)
  endif()

  # finally set a found variable for each MPI language
  if (MPI_${lang}_INCLUDE_PATH AND MPI_${lang}_LIBRARIES)
    set(MPI_${lang}_FOUND TRUE PARENT_SCOPE)
  else()
    set(MPI_${lang}_FOUND FALSE PARENT_SCOPE)
  endif()
endfunction()


# This function attempts to compile with the regular compiler, to see if MPI programs
# work with it.  This is a last ditch attempt after we've tried interrogating mpicc and
# friends, and after we've tried to find generic libraries.  Works on machines like
# Cray XE6, where the modules environment changes what MPI version cc, CC, and ftn use.
function(try_regular_compiler lang success)
  set(scratch_directory ${CMAKE_CURRENT_BINARY_DIR}${CMAKE_FILES_DIRECTORY})
  if (${lang} STREQUAL Fortran)
    set(test_file ${scratch_directory}/cmake_mpi_test.f90)
    file(WRITE ${test_file}
      "program hello\n"
      "include 'mpif.h'\n"
      "integer ierror\n"
      "call MPI_INIT(ierror)\n"
      "call MPI_FINALIZE(ierror)\n"
      "end\n")
  else()
    if (${lang} STREQUAL CXX)
      set(test_file ${scratch_directory}/cmake_mpi_test.cpp)
    else()
      set(test_file ${scratch_directory}/cmake_mpi_test.c)
    endif()
    file(WRITE ${test_file}
      "#include <mpi.h>\n"
      "int main(int argc, char **argv) {\n"
      "  MPI_Init(&argc, &argv);\n"
      "  MPI_Finalize();\n"
      "}\n")
  endif()
  try_compile(compiler_has_mpi ${scratch_directory} ${test_file})
  if (compiler_has_mpi)
    set(MPI_${lang}_NO_INTERROGATE ${CMAKE_${lang}_COMPILER} CACHE STRING "Whether to interrogate MPI ${lang} compiler" FORCE)
    set(MPI_${lang}_COMPILER       ${CMAKE_${lang}_COMPILER} CACHE STRING "MPI ${lang} compiler"                        FORCE)
    set(MPI_${lang}_COMPILE_FLAGS  ""                        CACHE STRING "MPI ${lang} compilation flags"               FORCE)
    set(MPI_${lang}_INCLUDE_PATH   ""                        CACHE STRING "MPI ${lang} include path"                    FORCE)
    set(MPI_${lang}_LINK_FLAGS     ""                        CACHE STRING "MPI ${lang} linking flags"                   FORCE)
    set(MPI_${lang}_LIBRARIES      ""                        CACHE STRING "MPI ${lang} libraries to link against"       FORCE)
  endif()
  set(${success} ${compiler_has_mpi} PARENT_SCOPE)
  unset(compiler_has_mpi CACHE)
endfunction()

# End definitions, commence real work here.

# Most mpi distros have some form of mpiexec which gives us something we can reliably look for.
find_program(MPIEXEC
  NAMES ${_MPI_EXEC_NAMES}
  PATHS ${_MPI_PREFIX_PATH}
  PATH_SUFFIXES bin
  DOC "Executable for running MPI programs.")

# call get_filename_component twice to remove mpiexec and the directory it exists in (typically bin).
# This gives us a fairly reliable base directory to search for /bin /lib and /include from.
get_filename_component(_MPI_BASE_DIR "${MPIEXEC}" PATH)
get_filename_component(_MPI_BASE_DIR "${_MPI_BASE_DIR}" PATH)

set(MPIEXEC_NUMPROC_FLAG "-np" CACHE STRING "Flag used by MPI to specify the number of processes for MPIEXEC; the next option will be the number of processes.")
set(MPIEXEC_PREFLAGS     ""    CACHE STRING "These flags will be directly before the executable that is being run by MPIEXEC.")
set(MPIEXEC_POSTFLAGS    ""    CACHE STRING "These flags will come after all flags given to MPIEXEC.")
set(MPIEXEC_MAX_NUMPROCS "2"   CACHE STRING "Maximum number of processors available to run MPI applications.")
mark_as_advanced(MPIEXEC MPIEXEC_NUMPROC_FLAG MPIEXEC_PREFLAGS MPIEXEC_POSTFLAGS MPIEXEC_MAX_NUMPROCS)


#=============================================================================
# Backward compatibility input hacks.  Propagate the FindMPI hints to C and
# CXX if the respective new versions are not defined.  Translate the old
# MPI_LIBRARY and MPI_EXTRA_LIBRARY to respective MPI_${lang}_LIBRARIES.
#
# Once we find the new variables, we translate them back into their old
# equivalents below.
foreach (lang C CXX)
  # Old input variables.
  set(_MPI_OLD_INPUT_VARS COMPILER COMPILE_FLAGS INCLUDE_PATH LINK_FLAGS)

  # Set new vars based on their old equivalents, if the new versions are not already set.
  foreach (var ${_MPI_OLD_INPUT_VARS})
    if (NOT MPI_${lang}_${var} AND MPI_${var})
      set(MPI_${lang}_${var} "${MPI_${var}}")
    endif()
  endforeach()

  # Special handling for MPI_LIBRARY and MPI_EXTRA_LIBRARY, which we nixed in the
  # new FindMPI.  These need to be merged into MPI_<lang>_LIBRARIES
  if (NOT MPI_${lang}_LIBRARIES AND (MPI_LIBRARY OR MPI_EXTRA_LIBRARY))
    set(MPI_${lang}_LIBRARIES ${MPI_LIBRARY} ${MPI_EXTRA_LIBRARY})
  endif()
endforeach()
#=============================================================================


# This loop finds the compilers and sends them off for interrogation.
foreach (lang C CXX Fortran)
  if (CMAKE_${lang}_COMPILER_WORKS)
    # If the user supplies a compiler *name* instead of an absolute path, assume that we need to find THAT compiler.
    if (MPI_${lang}_COMPILER)
      is_file_executable(MPI_${lang}_COMPILER MPI_COMPILER_IS_EXECUTABLE)
      if (NOT MPI_COMPILER_IS_EXECUTABLE)
        # Get rid of our default list of names and just search for the name the user wants.
        set(_MPI_${lang}_COMPILER_NAMES ${MPI_${lang}_COMPILER})
        set(MPI_${lang}_COMPILER "MPI_${lang}_COMPILER-NOTFOUND" CACHE FILEPATH "Cleared" FORCE)
        # If the user specifies a compiler, we don't want to try to search libraries either.
        set(try_libs FALSE)
      endif()
    else()
      set(try_libs TRUE)
    endif()

    find_program(MPI_${lang}_COMPILER
      NAMES  ${_MPI_${lang}_COMPILER_NAMES}
      PATHS  "${MPI_HOME}/bin" "$ENV{MPI_HOME}/bin" ${_MPI_PREFIX_PATH})
    interrogate_mpi_compiler(${lang} ${try_libs})
    mark_as_advanced(MPI_${lang}_COMPILER)

    # last ditch try -- if nothing works so far, just try running the regular compiler and
    # see if we can create an MPI executable.
    set(regular_compiler_worked 0)
    if (NOT MPI_${lang}_LIBRARIES OR NOT MPI_${lang}_INCLUDE_PATH)
      try_regular_compiler(${lang} regular_compiler_worked)
    endif()

    set(MPI_${lang}_FIND_QUIETLY ${MPI_FIND_QUIETLY})
    set(MPI_${lang}_FIND_REQUIRED ${MPI_FIND_REQUIRED})
    set(MPI_${lang}_FIND_VERSION ${MPI_FIND_VERSION})
    set(MPI_${lang}_FIND_VERSION_EXACT ${MPI_FIND_VERSION_EXACT})

    if (regular_compiler_worked)
      find_package_handle_standard_args(MPI_${lang} DEFAULT_MSG MPI_${lang}_COMPILER)
    else()
      find_package_handle_standard_args(MPI_${lang} DEFAULT_MSG MPI_${lang}_LIBRARIES MPI_${lang}_INCLUDE_PATH)
    endif()
  endif()
endforeach()


#=============================================================================
# More backward compatibility stuff
#
# Bare MPI sans ${lang} vars are set to CXX then C, depending on what was found.
# This mimics the behavior of the old language-oblivious FindMPI.
set(_MPI_OLD_VARS FOUND COMPILER INCLUDE_PATH COMPILE_FLAGS LINK_FLAGS LIBRARIES)
if (MPI_CXX_FOUND)
  foreach (var ${_MPI_OLD_VARS})
    set(MPI_${var} ${MPI_CXX_${var}})
  endforeach()
elseif (MPI_C_FOUND)
  foreach (var ${_MPI_OLD_VARS})
    set(MPI_${var} ${MPI_C_${var}})
  endforeach()
else()
  # Note that we might still have found Fortran, but you'll need to use MPI_Fortran_FOUND
  set(MPI_FOUND FALSE)
endif()

# Chop MPI_LIBRARIES into the old-style MPI_LIBRARY and MPI_EXTRA_LIBRARY, and set them in cache.
if (MPI_LIBRARIES)
  list(GET MPI_LIBRARIES 0 MPI_LIBRARY_WORK)
  set(MPI_LIBRARY ${MPI_LIBRARY_WORK} CACHE FILEPATH "MPI library to link against" FORCE)
else()
  set(MPI_LIBRARY "MPI_LIBRARY-NOTFOUND" CACHE FILEPATH "MPI library to link against" FORCE)
endif()

list(LENGTH MPI_LIBRARIES MPI_NUMLIBS)
if (MPI_NUMLIBS GREATER 1)
  set(MPI_EXTRA_LIBRARY_WORK ${MPI_LIBRARIES})
  list(REMOVE_AT MPI_EXTRA_LIBRARY_WORK 0)
  set(MPI_EXTRA_LIBRARY ${MPI_EXTRA_LIBRARY_WORK} CACHE STRING "Extra MPI libraries to link against" FORCE)
else()
  set(MPI_EXTRA_LIBRARY "MPI_EXTRA_LIBRARY-NOTFOUND" CACHE STRING "Extra MPI libraries to link against" FORCE)
endif()
#=============================================================================

# unset these vars to cleanup namespace
unset(_MPI_OLD_VARS)
unset(_MPI_PREFIX_PATH)
unset(_MPI_BASE_DIR)
foreach (lang C CXX Fortran)
  unset(_MPI_${lang}_COMPILER_NAMES)
endforeach()