[clang] [OpenMP] Introduce -fopenmp-force-usm flag (PR #75468)

[Joseph Huber via cfe-commits]

================
@@ -129,6 +129,22 @@ AMDGPUOpenMPToolChain::GetCXXStdlibType(const ArgList &Args) const {
 void AMDGPUOpenMPToolChain::AddClangSystemIncludeArgs(
     const ArgList &DriverArgs, ArgStringList &CC1Args) const {
   HostTC.AddClangSystemIncludeArgs(DriverArgs, CC1Args);
+
+  CC1Args.push_back("-internal-isystem");
+  SmallString<128> P(HostTC.getDriver().ResourceDir);
+  llvm::sys::path::append(P, "include/cuda_wrappers");
+  CC1Args.push_back(DriverArgs.MakeArgString(P));
+
+  // Force USM mode will forcefully include #pragma omp requires
+  // unified_shared_memory via the force_usm header
+  // XXX This may result in a compilation error if the source
+  // file already includes that pragma.
+  if (DriverArgs.hasArg(options::OPT_fopenmp_force_usm)) {
+    CC1Args.push_back("-include");
+    CC1Args.push_back(
+        DriverArgs.MakeArgString(HostTC.getDriver().ResourceDir +
+                                 "/include/openmp_wrappers/force_usm.h"));
----------------
jhuber6 wrote:

Here's the patch for `-fopenmp-offload-mandatory` which is a similar use-case https://reviews.llvm.org/D120353.

https://github.com/llvm/llvm-project/pull/75468