From f263bd8f7d4c82af9672803e6d8d57f25c929d00 Mon Sep 17 00:00:00 2001
From: Joseph Huber <jhuber6@vols.utk.edu>
Date: Mon, 27 Mar 2023 10:01:12 -0500
Subject: [PATCH] [Clang] Implicitly include LLVM libc headers for the GPU

There is currently work to support basic `libc` functionality on the
GPU. Some basic information about the projects can be found at
https://libc.llvm.org/gpu_mode.html. Typically, including the system
headers on the GPU will result in an error. For this reason the LLVM
`libc` project will generate its own headers that can be used with the
GPU.

The problem is that these headers will use the same name as the system headers.
For that reason, D146970 places it in the `llvm-libc` subfolder. In order to
still pick these files up, this patch adds changes in clang to default to
searching this directory when targeting the GPU. This lets offloading languages
such as OpenMP use the system `string.h` when compiling for the host and then
the LLVM libc `string.h` when targeting the GPU.

Depends on D146970

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D146973
---
 clang/lib/Driver/ToolChains/Clang.cpp | 18 ++++++++++++++++++
 clang/test/Driver/gpu-libc-headers.c  | 22 ++++++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 clang/test/Driver/gpu-libc-headers.c

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 41fe893..a17db9b 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1157,6 +1157,24 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
   if (JA.isOffloading(Action::OFK_HIP))
     getToolChain().AddHIPIncludeArgs(Args, CmdArgs);
 
+  // If we are compiling for a GPU target we want to override the system headers
+  // with ones created by the 'libc' project if present.
+  if (!Args.hasArg(options::OPT_nostdinc) &&
+      !Args.hasArg(options::OPT_nogpuinc) &&
+      !Args.hasArg(options::OPT_nobuiltininc) &&
+      (getToolChain().getTriple().isNVPTX() ||
+       getToolChain().getTriple().isAMDGCN())) {
+
+      // Add include/gpu-none-libc/* to our system include path. This lets us use
+      // GPU-specific system headers first. These headers should be made to be
+      // compatible with the host environment's headers.
+      SmallString<128> P(llvm::sys::path::parent_path(D.InstalledDir));
+      llvm::sys::path::append(P, "include");
+      llvm::sys::path::append(P, "gpu-none-llvm");
+      CmdArgs.push_back("-c-isystem");
+      CmdArgs.push_back(Args.MakeArgString(P));
+  }
+
   // If we are offloading to a target via OpenMP we need to include the
   // openmp_wrappers folder which contains alternative system headers.
   if (JA.isDeviceOffloading(Action::OFK_OpenMP) &&
diff --git a/clang/test/Driver/gpu-libc-headers.c b/clang/test/Driver/gpu-libc-headers.c
new file mode 100644
index 0000000..c8f772f
--- /dev/null
+++ b/clang/test/Driver/gpu-libc-headers.c
@@ -0,0 +1,22 @@
+// REQUIRES: nvptx-registered-target
+// REQUIRES: amdgpu-registered-target
+
+// RUN:   %clang -### --target=x86_64-unknown-linux-gnu -fopenmp=libomp --sysroot=./ \
+// RUN:     -fopenmp-targets=amdgcn-amd-amdhsa -Xopenmp-target=amdgcn-amd-amdhsa --offload-arch=gfx908  \
+// RUN:     -nogpulib %s 2>&1 | FileCheck %s --check-prefix=CHECK-HEADERS
+// RUN:   %clang -### --target=x86_64-unknown-linux-gnu -fopenmp=libomp --sysroot=./ \
+// RUN:     -fopenmp-targets=nvptx64-nvidia-cuda -Xopenmp-target=nvptx64-nvidia-cuda --offload-arch=sm_70  \
+// RUN:     -nogpulib %s 2>&1 | FileCheck %s --check-prefix=CHECK-HEADERS
+// RUN:   %clang -### --target=nvptx64-nvidia-cuda -march=sm_70 -nogpulib --sysroot=./ %s 2>&1 | \
+// RUN:     FileCheck %s --check-prefix=CHECK-HEADERS
+// RUN:   %clang -### --target=amdgcn-amd-amdhsa -mcpu=gfx1030 -nogpulib --sysroot=./ %s 2>&1 | \
+// RUN:     FileCheck %s --check-prefix=CHECK-HEADERS
+// CHECK-HEADERS: "-cc1"{{.*}}"-c-isystem" "{{.*}}include/gpu-none-llvm"{{.*}}"-isysroot" "./"
+
+// RUN:   %clang -### --target=amdgcn-amd-amdhsa -mcpu=gfx1030 -nogpulib \
+// RUN:     -nogpuinc %s 2>&1 | FileCheck %s --check-prefix=CHECK-HEADERS-DISABLED
+// RUN:   %clang -### --target=amdgcn-amd-amdhsa -mcpu=gfx1030 -nogpulib \
+// RUN:     -nostdinc %s 2>&1 | FileCheck %s --check-prefix=CHECK-HEADERS-DISABLED
+// RUN:   %clang -### --target=amdgcn-amd-amdhsa -mcpu=gfx1030 -nogpulib \
+// RUN:     -nobuiltininc %s 2>&1 | FileCheck %s --check-prefix=CHECK-HEADERS-DISABLED
+// CHECK-HEADERS-DISABLED-NOT: "-cc1"{{.*}}"-c-isystem" "{{.*}}include/gpu-none-llvm"
-- 
2.7.4