[NVPTX] Fix ctor / dtor lowering when NVPTX target is not enabled

[jhuber6]

Summary:
We pass the -nvptx-lower-global-ctor-dtor option to support the libc
like use-case which needs global constructors sometimes. This only
affects the backend. If the NVPTX target is not enabled this option will
be unknown which prevents you from compiling generic IR for this.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Joseph Huber (jhuber6)

Changes

Summary:
We pass the -nvptx-lower-global-ctor-dtor option to support the libc
like use-case which needs global constructors sometimes. This only
affects the backend. If the NVPTX target is not enabled this option will
be unknown which prevents you from compiling generic IR for this.

---

Full diff: https://github.com/llvm/llvm-project/pull/124116.diff

2 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Cuda.cpp (+4-1)
• (modified) clang/test/Driver/cuda-cross-compiling.c (+4)

diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index d4099216c81ba8..0922a97ed7c19d 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -639,6 +639,9 @@ void NVPTX::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   CmdArgs.push_back(
       Args.MakeArgString("--plugin-opt=-mattr=" + llvm::join(Features, ",")));
 
+  // Enable ctor / dtor lowering for the direct / freestanding NVPTX target.
+  CmdArgs.append({"-mllvm", "--nvptx-lower-global-ctor-dtor"});
+
   // Add paths for the default clang library path.
   SmallString<256> DefaultLibPath =
       llvm::sys::path::parent_path(TC.getDriver().Dir);
@@ -783,7 +786,7 @@ void NVPTXToolChain::addClangTargetOptions(
   // If we are compiling with a standalone NVPTX toolchain we want to try to
   // mimic a standard environment as much as possible. So we enable lowering
   // ctor / dtor functions to global symbols that can be registered.
-  if (Freestanding)
+  if (Freestanding && !getDriver().isUsingLTO())
     CC1Args.append({"-mllvm", "--nvptx-lower-global-ctor-dtor"});
 }
 
diff --git a/clang/test/Driver/cuda-cross-compiling.c b/clang/test/Driver/cuda-cross-compiling.c
index baf37048300315..7817e462c47be9 100644
--- a/clang/test/Driver/cuda-cross-compiling.c
+++ b/clang/test/Driver/cuda-cross-compiling.c
@@ -63,8 +63,12 @@
 //
 // RUN: %clang -target nvptx64-nvidia-cuda -march=sm_70 %s -### 2>&1 \
 // RUN:   | FileCheck -check-prefix=LOWERING %s
+// RUN: %clang -target nvptx64-nvidia-cuda -march=sm_70 -flto -c %s -### 2>&1 \
+// RUN:   | FileCheck -check-prefix=LOWERING-LTO %s
 
 // LOWERING: -cc1" "-triple" "nvptx64-nvidia-cuda" {{.*}} "-mllvm" "--nvptx-lower-global-ctor-dtor"
+// LOWERING: clang-nvlink-wrapper{{.*}} "-mllvm" "--nvptx-lower-global-ctor-dtor"
+// LOWERING-LTO-NOT: "--nvptx-lower-global-ctor-dtor"
 
 //
 // Test passing arguments directly to nvlink.

[jplehr]

Fixes a build issue I was hitting in #123673

[jhuber6]

Maybe some day we can just make this the default if we ever provide an in-tree way to handle CUDA.