[clang] [Clang] Add a flag to include GPU startup files (PR #112025)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/112025

Summary:
The C library for GPUs provides the ability to target regular C/C++
programs by providing the C library and a file containing kernels that
call the `main` function. This is mostly used for unit tests, this patch
provides a quick way to add them without needing to know the paths. I
currently do this explicitly, but according to the libc++ contributors
we don't want to need to specify these paths manually. See the
discussion in https://github.com/llvm/llvm-project/pull/104515.

I just default to `lib/` if the target-specific one isn't found because
the linker will handle giving a reasonable error message if it's not
found. Basically the use-case looks like this.

```console
$ clang test.c --target=amdgcn-amd-amdhsa -mcpu=native -gpustartfiles
$ amdhsa-loader a.out
PASS!
```


>From a014a06d5b06bb8c94b4d86636fb57f342e184db Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Fri, 11 Oct 2024 12:21:49 -0500
Subject: [PATCH] [Clang] Add a flag to include GPU startup files

Summary:
The C library for GPUs provides the ability to target regular C/C++
programs by providing the C library and a file containing kernels that
call the `main` function. This is mostly used for unit tests, this patch
provides a quick way to add them without needing to know the paths. I
currently do this explicitly, but according to the libc++ contributors
we don't want to need to specify these paths manually. See the
discussion in https://github.com/llvm/llvm-project/pull/104515.

I just default to `lib/` if the target-specific one isn't found because
the linker will handle giving a reasonable error message if it's not
found. Basically the use-case looks like this.

```console
$ clang test.c --target=amdgcn-amd-amdhsa -mcpu=native -gpustartfiles
$ amdhsa-loader a.out
PASS!
```
---
 clang/include/clang/Driver/Options.td  | 3 +++
 clang/lib/Driver/ToolChains/AMDGPU.cpp | 9 +++++++++
 clang/lib/Driver/ToolChains/Cuda.cpp   | 9 +++++++++
 clang/test/Driver/gpustartfiles.c      | 7 +++++++
 4 files changed, 28 insertions(+)
 create mode 100644 clang/test/Driver/gpustartfiles.c

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d306c751505e98..b7f7a7cb47f754 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1316,6 +1316,9 @@ defm offload_via_llvm : BoolFOption<"offload-via-llvm",
   BothFlags<[], [ClangOption], " LLVM/Offload as portable offloading runtime.">>;
 }
 
+def gpustartfiles : Flag<["-"], "gpustartfiles">, Group<Link_Group>,
+  HelpText<"Link the GPU C startup utilities automatically, used for testing.">;
+
 // CUDA options
 let Group = cuda_Group in {
 def cuda_include_ptx_EQ : Joined<["--"], "cuda-include-ptx=">,
diff --git a/clang/lib/Driver/ToolChains/AMDGPU.cpp b/clang/lib/Driver/ToolChains/AMDGPU.cpp
index 2c85d21ebd738c..9a648be4ea3915 100644
--- a/clang/lib/Driver/ToolChains/AMDGPU.cpp
+++ b/clang/lib/Driver/ToolChains/AMDGPU.cpp
@@ -648,6 +648,15 @@ void amdgpu::Linker::ConstructJob(Compilation &C, const JobAction &JA,
         Args.MakeArgString("-plugin-opt=-mattr=" + llvm::join(Features, ",")));
   }
 
+  if (Args.hasArg(options::OPT_gpustartfiles)) {
+    auto IncludePath = getToolChain().getStdlibPath();
+    if (!IncludePath)
+      IncludePath = "/lib";
+    SmallString<128> P(*IncludePath);
+    llvm::sys::path::append(P, "crt1.o");
+    CmdArgs.append({"-lc", "-lm", Args.MakeArgString(P)});
+  }
+
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
   C.addCommand(std::make_unique<Command>(
diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index 7a70cf1c5694fd..ff96ff989db630 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -641,6 +641,15 @@ void NVPTX::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   llvm::sys::path::append(DefaultLibPath, CLANG_INSTALL_LIBDIR_BASENAME);
   CmdArgs.push_back(Args.MakeArgString(Twine("-L") + DefaultLibPath));
 
+  if (Args.hasArg(options::OPT_gpustartfiles)) {
+    auto IncludePath = getToolChain().getStdlibPath();
+    if (!IncludePath)
+      IncludePath = "/lib";
+    SmallString<128> P(*IncludePath);
+    llvm::sys::path::append(P, "crt1.o");
+    CmdArgs.append({"-lc", "-lm", Args.MakeArgString(P)});
+  }
+
   C.addCommand(std::make_unique<Command>(
       JA, *this,
       ResponseFileSupport{ResponseFileSupport::RF_Full, llvm::sys::WEM_UTF8,
diff --git a/clang/test/Driver/gpustartfiles.c b/clang/test/Driver/gpustartfiles.c
new file mode 100644
index 00000000000000..c1b7a6fa922df4
--- /dev/null
+++ b/clang/test/Driver/gpustartfiles.c
@@ -0,0 +1,7 @@
+// RUN: %clang -target nvptx64-nvidia-cuda -march=sm_61 -gpustartfiles \
+// RUN:   -nogpulib -nogpuinc -### %s 2>&1 | FileCheck -check-prefix=NVPTX %s
+// NVPTX: clang-nvlink-wrapper{{.*}}"-lc" "-lm" "{{.*}}crt1.o"
+//
+// RUN: %clang -target amdgcn-amd-amdhsa -march=gfx90a -gpustartfiles \
+// RUN:   -nogpulib -nogpuinc -### %s 2>&1 | FileCheck -check-prefix=AMDGPU %s
+// AMDGPU: ld.lld{{.*}}"-lc" "-lm" "{{.*}}crt1.o"