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

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: Jan Patrick Lehr (jplehr)

<details>
<summary>Changes</summary>

The new flag implements logic to include `#pragma omp requires unified_shared_memory` in every translation unit.
This enables a straightforward way to enable USM for an application without the need to modify sources.

This is the flag mentioned in https://github.com/llvm/llvm-project/pull/75467
Once the test landed, I'll rebase and enable the test with this patch.

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


4 Files Affected:

- (modified) clang/include/clang/Driver/Options.td (+2) 
- (modified) clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp (+14) 
- (modified) clang/lib/Headers/CMakeLists.txt (+1) 
- (added) clang/lib/Headers/openmp_wrappers/usm/force_usm.h (+6) 


``````````diff
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 1b02087425b751..b9cd3043a13a9a 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3381,6 +3381,8 @@ def fopenmp_cuda_blocks_per_sm_EQ : Joined<["-"], "fopenmp-cuda-blocks-per-sm=">
   Flags<[NoArgumentUnused, HelpHidden]>, Visibility<[ClangOption, CC1Option]>;
 def fopenmp_cuda_teams_reduction_recs_num_EQ : Joined<["-"], "fopenmp-cuda-teams-reduction-recs-num=">, Group<f_Group>,
   Flags<[NoArgumentUnused, HelpHidden]>, Visibility<[ClangOption, CC1Option]>;
+def fopenmp_force_usm : Flag<["-"], "fopenmp-force-usm">, Group<f_Group>,
+  Flags<[NoArgumentUnused, HelpHidden]>, Visibility<[CC1Option]>;
 
 //===----------------------------------------------------------------------===//
 // Shared cc1 + fc1 OpenMP Target Options
diff --git a/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp b/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp
index b012b7cb729378..2484a59085c276 100644
--- a/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp
+++ b/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp
@@ -129,6 +129,20 @@ 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 APU mode will focefully include #pragma omp requires
+  // unified_shared_memory via the force_usm header
+  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"));
+  }
 }
 
 void AMDGPUOpenMPToolChain::AddIAMCUIncludeArgs(const ArgList &Args,
diff --git a/clang/lib/Headers/CMakeLists.txt b/clang/lib/Headers/CMakeLists.txt
index f8fdd402777e48..aac232fa8b4405 100644
--- a/clang/lib/Headers/CMakeLists.txt
+++ b/clang/lib/Headers/CMakeLists.txt
@@ -319,6 +319,7 @@ set(openmp_wrapper_files
   openmp_wrappers/__clang_openmp_device_functions.h
   openmp_wrappers/complex_cmath.h
   openmp_wrappers/new
+  openmp_wrappers/usm/force_usm.h
 )
 
 set(llvm_libc_wrapper_files
diff --git a/clang/lib/Headers/openmp_wrappers/usm/force_usm.h b/clang/lib/Headers/openmp_wrappers/usm/force_usm.h
new file mode 100644
index 00000000000000..15c394e27ce9c2
--- /dev/null
+++ b/clang/lib/Headers/openmp_wrappers/usm/force_usm.h
@@ -0,0 +1,6 @@
+#ifndef __CLANG_FORCE_OPENMP_USM
+#define __CLANG_FORCE_OPENMP_USM
+
+#pragma omp requires unified_shared_memory
+
+#endif

``````````

</details>


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