[OpenMP] Implicit USM Clause Solution

This uses an implicitly added OpenMP USM Clause when initializing SEMA
to enforce the use of USM.

Author: jplehr

clang/include/clang/Basic/LangOptions.def

@@ -260,6 +260,7 @@ LANGOPT(OpenMPTeamSubscription  , 1, 0, "Assume distributed loops do not have mo
 LANGOPT(OpenMPNoThreadState  , 1, 0, "Assume that no thread in a parallel region will modify an ICV.")
 LANGOPT(OpenMPNoNestedParallelism  , 1, 0, "Assume that no thread in a parallel region will encounter a parallel region")
 LANGOPT(OpenMPOffloadMandatory  , 1, 0, "Assert that offloading is mandatory and do not create a host fallback.")
+LANGOPT(OpenMPForceUSM     , 1, 0, "Enable OpenMP unified shared memory mode via compiler.")
 LANGOPT(NoGPULib  , 1, 0, "Indicate a build without the standard GPU libraries.")
 LANGOPT(RenderScript      , 1, 0, "RenderScript")
 

clang/include/clang/Driver/Options.td

@@ -3451,6 +3451,10 @@ def fopenmp_offload_mandatory : Flag<["-"], "fopenmp-offload-mandatory">, Group<
   Flags<[NoArgumentUnused]>, Visibility<[ClangOption, CC1Option]>,
   HelpText<"Do not create a host fallback if offloading to the device fails.">,
   MarshallingInfoFlag<LangOpts<"OpenMPOffloadMandatory">>;
+def fopenmp_force_usm : Flag<["-"], "fopenmp-force-usm">, Group<f_Group>,
+  Flags<[NoArgumentUnused]>, Visibility<[ClangOption, CC1Option]>,
+  HelpText<"Force behvaior as if the user specified pragma omp requires unified_shared_memory.">,
+  MarshallingInfoFlag<LangOpts<"OpenMPForceUSM">>;
 def fopenmp_target_jit : Flag<["-"], "fopenmp-target-jit">, Group<f_Group>,
   Flags<[NoArgumentUnused]>, Visibility<[ClangOption, CLOption]>,
   HelpText<"Emit code that can be JIT compiled for OpenMP offloading. Implies -foffload-lto=full">;

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -1044,6 +1044,12 @@ CGOpenMPRuntime::CGOpenMPRuntime(CodeGenModule &CGM)
                                          ? CGM.getLangOpts().OMPHostIRFile
                                          : StringRef{});
   OMPBuilder.setConfig(Config);
+
+  // The user forces the compiler to behave as if omp requires unified_shared_memory was given.
+  if (CGM.getLangOpts().OpenMPForceUSM) {
+    HasRequiresUnifiedSharedMemory = true;
+    OMPBuilder.Config.setHasRequiresUnifiedSharedMemory(true);
+  }
 }
 
 void CGOpenMPRuntime::clear() {

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6382,6 +6382,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
         CmdArgs.push_back("-fopenmp-assume-no-nested-parallelism");
       if (Args.hasArg(options::OPT_fopenmp_offload_mandatory))
         CmdArgs.push_back("-fopenmp-offload-mandatory");
+      if (Args.hasArg(options::OPT_fopenmp_force_usm))
+        CmdArgs.push_back("-fopenmp-force-usm");
       break;
     default:
       // By default, if Clang doesn't know how to generate useful OpenMP code