FindThreads: Drop IRIX-specific options and results

We do not need to support IRIX anymore, so drop relevant parts.  In
particular, the `CMAKE_THREAD_PREFER_PTHREAD` is frequently confused
with `THREADS_PREFER_PTHREAD_FLAG`.

Also remove references to the IRIX-specific options and results
from other modules and tests.

7 files changed, 44 insertions, 81 deletions

diff --git a/Modules/CMakeBackwardCompatibilityC.cmake b/Modules/CMakeBackwardCompatibilityC.cmake
index 5d86d73..775a513 100644
--- a/Modules/CMakeBackwardCompatibilityC.cmake
+++ b/Modules/CMakeBackwardCompatibilityC.cmake
@@ -59,9 +59,6 @@ if(NOT CMAKE_SKIP_COMPATIBILITY_TESTS)
   set (CMAKE_HP_PTHREADS        ${CMAKE_HP_PTHREADS_INIT} CACHE BOOL
      "Use HP pthreads.")
 
-  set (CMAKE_USE_SPROC          ${CMAKE_USE_SPROC_INIT} CACHE BOOL
-     "Use sproc libs.")
-
   if(__ERASE_CMAKE_TRY_COMPILE_OSX_ARCHITECTURES)
     set(CMAKE_TRY_COMPILE_OSX_ARCHITECTURES)
     set(__ERASE_CMAKE_TRY_COMPILE_OSX_ARCHITECTURES)
@@ -72,7 +69,6 @@ mark_as_advanced(
 CMAKE_HP_PTHREADS
 CMAKE_THREAD_LIBS
 CMAKE_USE_PTHREADS
-CMAKE_USE_SPROC
 CMAKE_USE_WIN32_THREADS
 CMAKE_X_CFLAGS
 CMAKE_X_LIBS
diff --git a/Modules/FindCUDA.cmake b/Modules/FindCUDA.cmake
index 0f5cab4..228eed4 100644
--- a/Modules/FindCUDA.cmake
+++ b/Modules/FindCUDA.cmake
@@ -875,11 +875,7 @@ endif()
 
 if(CUDA_USE_STATIC_CUDA_RUNTIME)
   if(UNIX)
-    # Check for the dependent libraries.  Here we look for pthreads.
-    if (DEFINED CMAKE_THREAD_PREFER_PTHREAD)
-      set(_cuda_cmake_thread_prefer_pthread ${CMAKE_THREAD_PREFER_PTHREAD})
-    endif()
-    set(CMAKE_THREAD_PREFER_PTHREAD 1)
+    # Check for the dependent libraries.
 
     # Many of the FindXYZ CMake comes with makes use of try_compile with int main(){return 0;}
     # as the source file.  Unfortunately this causes a warning with -Wstrict-prototypes and
@@ -890,13 +886,6 @@ if(CUDA_USE_STATIC_CUDA_RUNTIME)
     find_package(Threads REQUIRED)
     set(CMAKE_C_FLAGS ${_cuda_cmake_c_flags})
 
-    if (DEFINED _cuda_cmake_thread_prefer_pthread)
-      set(CMAKE_THREAD_PREFER_PTHREAD ${_cuda_cmake_thread_prefer_pthread})
-      unset(_cuda_cmake_thread_prefer_pthread)
-    else()
-      unset(CMAKE_THREAD_PREFER_PTHREAD)
-    endif()
-
     if(NOT APPLE)
       #On Linux, you must link against librt when using the static cuda runtime.
       find_library(CUDA_rt_LIBRARY rt)
diff --git a/Modules/FindDCMTK.cmake b/Modules/FindDCMTK.cmake
index 302c089..111e0ff 100644
--- a/Modules/FindDCMTK.cmake
+++ b/Modules/FindDCMTK.cmake
@@ -200,7 +200,6 @@ if(DCMTK_oflog_LIBRARY_RELEASE OR DCMTK_oflog_LIBRARY_DEBUG)
   # Hack - Not having a DCMTKConfig.cmake file to read the settings from, we will attempt to
   # find the library in all cases.
   # Ideally, pthread library should be discovered only if DCMTK_WITH_THREADS is enabled.
-  set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
   find_package(Threads)
 endif()
 
diff --git a/Modules/FindThreads.cmake b/Modules/FindThreads.cmake
index 691b1b7..9c96a1b 100644
--- a/Modules/FindThreads.cmake
+++ b/Modules/FindThreads.cmake
@@ -12,7 +12,6 @@ The following variables are set
 ::
 
   CMAKE_THREAD_LIBS_INIT     - the thread library
-  CMAKE_USE_SPROC_INIT       - are we using sproc?
   CMAKE_USE_WIN32_THREADS_INIT - using WIN32 threads?
   CMAKE_USE_PTHREADS_INIT    - are we using pthreads
   CMAKE_HP_PTHREADS_INIT     - are we using hp pthreads
@@ -23,12 +22,6 @@ The following import target is created
 
   Threads::Threads
 
-For systems with multiple thread libraries, caller can set
-
-::
-
-  CMAKE_THREAD_PREFER_PTHREAD
-
 If the use of the -pthread compiler and linker flag is preferred then the
 caller can set
 
@@ -55,12 +48,6 @@ else()
   message(FATAL_ERROR "FindThreads only works if either C or CXX language is enabled")
 endif()
 
-# Do we have sproc?
-if(CMAKE_SYSTEM_NAME MATCHES IRIX AND NOT CMAKE_THREAD_PREFER_PTHREAD)
-  include (CheckIncludeFiles)
-  CHECK_INCLUDE_FILES("sys/types.h;sys/prctl.h"  CMAKE_HAVE_SPROC_H)
-endif()
-
 # Internal helper macro.
 # Do NOT even think about using it outside of this file!
 macro(_check_threads_lib LIBNAME FUNCNAME VARNAME)
@@ -113,58 +100,53 @@ macro(_check_pthreads_flag)
   endif()
 endmacro()
 
-if(CMAKE_HAVE_SPROC_H AND NOT CMAKE_THREAD_PREFER_PTHREAD)
-  # We have sproc
-  set(CMAKE_USE_SPROC_INIT 1)
+# Do we have pthreads?
+if(CMAKE_C_COMPILER_LOADED)
+  CHECK_INCLUDE_FILE("pthread.h" CMAKE_HAVE_PTHREAD_H)
 else()
-  # Do we have pthreads?
-  if(CMAKE_C_COMPILER_LOADED)
-    CHECK_INCLUDE_FILE("pthread.h" CMAKE_HAVE_PTHREAD_H)
-  else()
-    CHECK_INCLUDE_FILE_CXX("pthread.h" CMAKE_HAVE_PTHREAD_H)
-  endif()
-  if(CMAKE_HAVE_PTHREAD_H)
-
-    #
-    # We have pthread.h
-    # Let's check for the library now.
-    #
-    set(CMAKE_HAVE_THREADS_LIBRARY)
-    if(NOT THREADS_HAVE_PTHREAD_ARG)
-      # Check if pthread functions are in normal C library.
-      # If the pthread functions already exist in C library, we could just use
-      # them instead of linking to the additional pthread library. We could
-      # try to check any pthread symbol name, but here is an exception. If we
-      # use clang asan build, we will find the pthread_create() symbol in the
-      # libc(libasan). However, it doesn't have the full pthread implementation.
-      # So, we can't assume that we have the pthread implementation in libc
-      # using the pthread_create() checking here. Then, we turn to check the
-      # pthread_kill() symbol instead.
-      CHECK_SYMBOL_EXISTS(pthread_kill pthread.h CMAKE_HAVE_LIBC_PTHREAD_KILL)
-      if(CMAKE_HAVE_LIBC_PTHREAD_KILL)
-        set(CMAKE_THREAD_LIBS_INIT "")
-        set(CMAKE_HAVE_THREADS_LIBRARY 1)
-        set(Threads_FOUND TRUE)
-      else()
-
-        # Check for -pthread first if enabled. This is the recommended
-        # way, but not backwards compatible as one must also pass -pthread
-        # as compiler flag then.
-        if (THREADS_PREFER_PTHREAD_FLAG)
-           _check_pthreads_flag()
-        endif ()
-
-        _check_threads_lib(pthreads pthread_create CMAKE_HAVE_PTHREADS_CREATE)
-        _check_threads_lib(pthread  pthread_create CMAKE_HAVE_PTHREAD_CREATE)
-        if(CMAKE_SYSTEM_NAME MATCHES "SunOS")
-            # On sun also check for -lthread
-            _check_threads_lib(thread thr_create CMAKE_HAVE_THR_CREATE)
-        endif()
+  CHECK_INCLUDE_FILE_CXX("pthread.h" CMAKE_HAVE_PTHREAD_H)
+endif()
+if(CMAKE_HAVE_PTHREAD_H)
+
+  #
+  # We have pthread.h
+  # Let's check for the library now.
+  #
+  set(CMAKE_HAVE_THREADS_LIBRARY)
+  if(NOT THREADS_HAVE_PTHREAD_ARG)
+    # Check if pthread functions are in normal C library.
+    # If the pthread functions already exist in C library, we could just use
+    # them instead of linking to the additional pthread library. We could
+    # try to check any pthread symbol name, but here is an exception. If we
+    # use clang asan build, we will find the pthread_create() symbol in the
+    # libc(libasan). However, it doesn't have the full pthread implementation.
+    # So, we can't assume that we have the pthread implementation in libc
+    # using the pthread_create() checking here. Then, we turn to check the
+    # pthread_kill() symbol instead.
+    CHECK_SYMBOL_EXISTS(pthread_kill pthread.h CMAKE_HAVE_LIBC_PTHREAD_KILL)
+    if(CMAKE_HAVE_LIBC_PTHREAD_KILL)
+      set(CMAKE_THREAD_LIBS_INIT "")
+      set(CMAKE_HAVE_THREADS_LIBRARY 1)
+      set(Threads_FOUND TRUE)
+    else()
+
+      # Check for -pthread first if enabled. This is the recommended
+      # way, but not backwards compatible as one must also pass -pthread
+      # as compiler flag then.
+      if (THREADS_PREFER_PTHREAD_FLAG)
+         _check_pthreads_flag()
+      endif ()
+
+      _check_threads_lib(pthreads pthread_create CMAKE_HAVE_PTHREADS_CREATE)
+      _check_threads_lib(pthread  pthread_create CMAKE_HAVE_PTHREAD_CREATE)
+      if(CMAKE_SYSTEM_NAME MATCHES "SunOS")
+          # On sun also check for -lthread
+          _check_threads_lib(thread thr_create CMAKE_HAVE_THR_CREATE)
       endif()
     endif()
-
-    _check_pthreads_flag()
   endif()
+
+  _check_pthreads_flag()
 endif()
 
 if(CMAKE_THREAD_LIBS_INIT OR CMAKE_HAVE_LIBC_PTHREAD_KILL)
diff --git a/Modules/Qt4ConfigDependentSettings.cmake b/Modules/Qt4ConfigDependentSettings.cmake
index 684ec21..4699ecd 100644
--- a/Modules/Qt4ConfigDependentSettings.cmake
+++ b/Modules/Qt4ConfigDependentSettings.cmake
@@ -256,7 +256,6 @@ if(Q_WS_X11)
   # X11 libraries Qt always depends on
   set(QT_QTGUI_LIB_DEPENDENCIES ${QT_QTGUI_LIB_DEPENDENCIES} ${X11_Xext_LIB} ${X11_X11_LIB})
 
-  set(CMAKE_THREAD_PREFER_PTHREAD 1)
   find_package(Threads)
   if(CMAKE_USE_PTHREADS_INIT)
     set(QT_QTCORE_LIB_DEPENDENCIES ${QT_QTCORE_LIB_DEPENDENCIES} ${CMAKE_THREAD_LIBS_INIT})
diff --git a/Tests/FindThreads/C-only/CMakeLists.txt b/Tests/FindThreads/C-only/CMakeLists.txt
index ab4ca0d..ee2a5f9 100644
--- a/Tests/FindThreads/C-only/CMakeLists.txt
+++ b/Tests/FindThreads/C-only/CMakeLists.txt
@@ -1,7 +1,6 @@
 cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
 project(FindThreads_C-only C)
 
-set(CMAKE_THREAD_PREFER_PTHREAD On)
 find_package(Threads REQUIRED)
 
 if (NOT WIN32)
diff --git a/Tests/FindThreads/CXX-only/CMakeLists.txt b/Tests/FindThreads/CXX-only/CMakeLists.txt
index 9993123..3c6cc1e 100644
--- a/Tests/FindThreads/CXX-only/CMakeLists.txt
+++ b/Tests/FindThreads/CXX-only/CMakeLists.txt
@@ -1,7 +1,6 @@
 cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
 project(FindThreads_CXX-only CXX)
 
-set(CMAKE_THREAD_PREFER_PTHREAD On)
 find_package(Threads REQUIRED)
 
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/../../../Modules/CheckForPthreads.c