[OPENMP] Allow to disable OpenMP support and link libgomp

[ABataev]

Summary

Added flag ENABLE_CLANG_OPENMP that is ON by default. If set to OFF, changes behavior of -fopenmp option to the old one.

[emaste]

I'm curious - what is the use case for the old behaviour?

AFAICT if the user sets Enable OpenMP support OFF they'll get a compiler that links against libgomp when -fopenmp is specified, but doesn't produce a useful openmp executable?

test/OpenMP/linking_no_openmp.c

2

-fopenmp=libgomp?

[emaste]

In D9875#175604, @emaste wrote:

I'm curious - what is the use case for the old behaviour?

Ah, I found Chandler's explanation for this, in the thread for r237769.

[• jhowarth]

I am not having any luck with this proposed patch. Building current llvm/clang/openmp/compiler-rt trunk with it produces a compiler that always defaults to emitting -lgomp for -fopenmp even if cmake is explicitly passed -DENABLE_CLANG_OPENMP=ON.

[ABataev]

Already has been fixed by Richard Smith.

[chandlerc]

Yea, i think Daniel's patch was a closer start. Anyways, thanks for taking
a stab at this.

CMakeLists.txt

if (CLANG_BUILT_STANDALONE)
 
   # Also copy ClangConfig.cmake to the build directory so that dependent projects
   # can build against a build directory of Clang more easily.
   configure_file(
     ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules/ClangConfig.cmake
     ${CLANG_BINARY_DIR}/share/clang/cmake/ClangConfig.cmake
     COPYONLY)
 endif ()
+
+option(ENABLE_CLANG_OPENMP "Enable OpenMP support." ON)
+if (ENABLE_CLANG_OPENMP)
+  set(CLANG_ENABLE_OPENMP "1")
+  add_definitions(-DENABLE_CLANG_OPENMP)
+else()
+  set(CLANG_ENABLE_OPENMP "0")
+endif()
+

lib/Driver/Tools.cpp

#ifdef LLVM_ON_UNIX
   std::string UID = llvm::utostr(getuid());
 #else
   // FIXME: Windows seems to have an 'SID' that might work.
   std::string UID = "9999";
 #endif
   Result.append(UID.begin(), UID.end());
 }
 
+enum LibOpenMP {
+  LibUnknown,
+  LibGOMP,
+  LibIOMP5
+};
+
 void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                          const InputInfo &Output,
                          const InputInfoList &Inputs,
                          const ArgList &Args,
                          const char *LinkingOutput) const {
   bool KernelOrKext = Args.hasArg(options::OPT_mkernel,
                                   options::OPT_fapple_kext);
   const Driver &D = getToolChain().getDriver();

   // AltiVec language extensions aren't relevant for assembling.
   if (!isa<PreprocessJobAction>(JA) || 
       Output.getType() != types::TY_PP_Asm)
     Args.AddLastArg(CmdArgs, options::OPT_faltivec);
   Args.AddLastArg(CmdArgs, options::OPT_fdiagnostics_show_template_tree);
   Args.AddLastArg(CmdArgs, options::OPT_fno_elide_type);
 
   // Forward flags for OpenMP
-  if (Args.hasArg(options::OPT_fopenmp_EQ) ||
-      Args.hasArg(options::OPT_fopenmp)) {
+  LibOpenMP UsedOpenMPLib = LibUnknown;
+  if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_EQ)) {
+    UsedOpenMPLib = llvm::StringSwitch<LibOpenMP>(A->getValue())
+        .Case("libgomp",  LibGOMP)
+        .Case("libiomp5", LibIOMP5)
+        .Default(LibUnknown);
+    if (UsedOpenMPLib == LibUnknown)
+      getToolChain().getDriver().Diag(diag::err_drv_unsupported_option_argument)
+        << A->getOption().getName() << A->getValue();
+  } else if (Args.hasArg(options::OPT_fopenmp)) {
+#ifdef ENABLE_CLANG_OPENMP
+    UsedOpenMPLib = LibIOMP5;
+#else
+    UsedOpenMPLib = LibGOMP;
+#endif // ENABLE_CLANG_OPENMP
+  }
+  if (UsedOpenMPLib == LibIOMP5) {
     CmdArgs.push_back("-fopenmp");
   }
 
   const SanitizerArgs &Sanitize = getToolChain().getSanitizerArgs();
   Sanitize.addArgs(Args, CmdArgs);
 
   // Report an error for -faltivec on anything other than PowerPC.
   if (const Arg *A = Args.getLastArg(options::OPT_faltivec))
void darwin::Link::AddLinkArgs(Compilation &C,
   Args.AddAllArgs(CmdArgs, options::OPT_segcreate);
   Args.AddLastArg(CmdArgs, options::OPT_whyload);
   Args.AddLastArg(CmdArgs, options::OPT_whatsloaded);
   Args.AddAllArgs(CmdArgs, options::OPT_dylinker__install__name);
   Args.AddLastArg(CmdArgs, options::OPT_dylinker);
   Args.AddLastArg(CmdArgs, options::OPT_Mach);
 }
 
-enum LibOpenMP {
-  LibUnknown,
-  LibGOMP,
-  LibIOMP5
-};
-
 void darwin::Link::ConstructJob(Compilation &C, const JobAction &JA,
                                 const InputInfo &Output,
                                 const InputInfoList &Inputs,
                                 const ArgList &Args,
                                 const char *LinkingOutput) const {
   assert(Output.getType() == types::TY_Image && "Invalid linker output type.");
 
   // If the number of arguments surpasses the system limits, we will encode the
if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_EQ)) {
     UsedOpenMPLib = llvm::StringSwitch<LibOpenMP>(A->getValue())
         .Case("libgomp",  LibGOMP)
         .Case("libiomp5", LibIOMP5)
         .Default(LibUnknown);
     if (UsedOpenMPLib == LibUnknown)
       getToolChain().getDriver().Diag(diag::err_drv_unsupported_option_argument)
         << A->getOption().getName() << A->getValue();
   } else if (Args.hasArg(options::OPT_fopenmp)) {
+#ifdef ENABLE_CLANG_OPENMP
     UsedOpenMPLib = LibIOMP5;
+#else
+    UsedOpenMPLib = LibGOMP;
+#endif // ENABLE_CLANG_OPENMP
   }
   switch (UsedOpenMPLib) {
   case LibGOMP:
     CmdArgs.push_back("-lgomp");
     break;
   case LibIOMP5:
     CmdArgs.push_back("-liomp5");
     break;
if (!Args.hasArg(options::OPT_nodefaultlibs)) {
         UsedOpenMPLib = llvm::StringSwitch<LibOpenMP>(A->getValue())
                             .Case("libgomp", LibGOMP)
                             .Case("libiomp5", LibIOMP5)
                             .Default(LibUnknown);
         if (UsedOpenMPLib == LibUnknown)
           D.Diag(diag::err_drv_unsupported_option_argument)
               << A->getOption().getName() << A->getValue();
       } else if (Args.hasArg(options::OPT_fopenmp)) {
+#ifdef ENABLE_CLANG_OPENMP
         UsedOpenMPLib = LibIOMP5;
+#else
+        UsedOpenMPLib = LibGOMP;
+#endif // ENABLE_CLANG_OPENMP
       }
       switch (UsedOpenMPLib) {
       case LibGOMP:
         CmdArgs.push_back("-lgomp");
 
         // FIXME: Exclude this for platforms with libgomp that don't require
         // librt. Most modern Linux platforms require it, but some may not.
         CmdArgs.push_back("-lrt");

test/OpenMP/linking.c

 // Test the that the driver produces reasonable linker invocations with
 // -fopenmp or -fopenmp|libgomp.
+// REQUIRES: openmp
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -fopenmp -target i386-unknown-linux \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-32 %s
 // CHECK-LD-32: "{{.*}}ld{{(.exe)?}}"
 // CHECK-LD-32: "-liomp5" "-lgcc"
 // CHECK-LD-32: "-lpthread" "-lc"
 //

test/OpenMP/linking_no_openmp.c

+// Test the that the driver produces reasonable linker invocations with
+// -fopenmp or -fopenmp|libgomp.
+// REQUIRES: no_openmp
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp -target i386-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-LD-32 %s
+// CHECK-LD-32: "{{.*}}ld{{(.exe)?}}"
+// CHECK-LD-32: "-lgomp" "-lrt" "-lgcc"
+// CHECK-LD-32: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp -target x86_64-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-LD-64 %s
+// CHECK-LD-64: "{{.*}}ld{{(.exe)?}}"
+// CHECK-LD-64: "-lgomp" "-lrt" "-lgcc"
+// CHECK-LD-64: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp=libgomp -target i386-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-GOMP-LD-32 %s
+// CHECK-GOMP-LD-32: "{{.*}}ld{{(.exe)?}}"
+// CHECK-GOMP-LD-32: "-lgomp" "-lrt" "-lgcc"
+// CHECK-GOMP-LD-32: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp=libgomp -target x86_64-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-GOMP-LD-64 %s
+// CHECK-GOMP-LD-64: "{{.*}}ld{{(.exe)?}}"
+// CHECK-GOMP-LD-64: "-lgomp" "-lrt" "-lgcc"
+// CHECK-GOMP-LD-64: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp -target i386-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-IOMP5-LD-32 %s
+// CHECK-IOMP5-LD-32: "{{.*}}ld{{(.exe)?}}"
+// CHECK-IOMP5-LD-32: "-lgomp" "-lrt" "-lgcc"
+// CHECK-IOMP5-LD-32: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp -target x86_64-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-IOMP5-LD-64 %s
+// CHECK-IOMP5-LD-64: "{{.*}}ld{{(.exe)?}}"
+// CHECK-IOMP5-LD-64: "-lgomp" "-lrt" "-lgcc"
+// CHECK-IOMP5-LD-64: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp=lib -target i386-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-LIB-LD-32 %s
+// CHECK-LIB-LD-32: error: unsupported argument 'lib' to option 'fopenmp='
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp=lib -target x86_64-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-LIB-LD-64 %s
+// CHECK-LIB-LD-64: error: unsupported argument 'lib' to option 'fopenmp='
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp -fopenmp=libgomp -target i386-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-LD-OVERRIDE-32 %s
+// CHECK-LD-OVERRIDE-32: "{{.*}}ld{{(.exe)?}}"
+// CHECK-LD-OVERRIDE-32: "-lgomp" "-lrt" "-lgcc"
+// CHECK-LD-OVERRIDE-32: "-lpthread" "-lc"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -fopenmp -fopenmp=libgomp -target x86_64-unknown-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-LD-OVERRIDE-64 %s
+// CHECK-LD-OVERRIDE-64: "{{.*}}ld{{(.exe)?}}"
+// CHECK-LD-OVERRIDE-64: "-lgomp" "-lrt" "-lgcc"
+// CHECK-LD-OVERRIDE-64: "-lpthread" "-lc"
+//

test/lit.cfg

if has_plugins and config.llvm_plugin_ext:
     config.available_features.add('plugins')
 
 config.substitutions.append( ('%llvmshlibdir', config.llvm_shlib_dir) )
 config.substitutions.append( ('%pluginext', config.llvm_plugin_ext) )
 
 if config.clang_examples:
     config.available_features.add('examples')
 
+if config.clang_openmp:
+    config.available_features.add('openmp')
+else:
+    config.available_features.add('no_openmp')
+
 # Note that when substituting %clang_cc1 also fill in the include directory of
 # the builtin headers. Those are part of even a freestanding environment, but
 # Clang relies on the driver to locate them.
 def getClangBuiltinIncludeDir(clang):
     # FIXME: Rather than just getting the version, we should have clang print
     # out its resource dir here in an easy to scrape form.
     cmd = subprocess.Popen([clang, '-print-file-name=include'],
                            stdout=subprocess.PIPE,

test/lit.site.cfg.in

 config.target_triple = "@TARGET_TRIPLE@"
 config.llvm_use_sanitizer = "@LLVM_USE_SANITIZER@"
 config.clang_arcmt = @ENABLE_CLANG_ARCMT@
 config.clang_staticanalyzer = @ENABLE_CLANG_STATIC_ANALYZER@
 config.clang_examples = @ENABLE_CLANG_EXAMPLES@
 config.enable_shared = @ENABLE_SHARED@
 config.enable_backtrace = "@ENABLE_BACKTRACES@"
 config.host_arch = "@HOST_ARCH@"
+config.clang_openmp = "@CLANG_ENABLE_OPENMP@"
 
 # Support substitution of the tools and libs dirs with user parameters. This is
 # used when we can't determine the tool dir at configuration time.
 try:
     config.clang_tools_dir = config.clang_tools_dir % lit_config.params
     config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
     config.llvm_shlib_dir = config.llvm_shlib_dir % lit_config.params
     config.llvm_libs_dir = config.llvm_libs_dir % lit_config.params
 except KeyError:
     e = sys.exc_info()[1]
     key, = e.args
     lit_config.fatal("unable to find %r parameter, use '--param=%s=VALUE'" % (key,key))
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@CLANG_SOURCE_DIR@/test/lit.cfg")