[clang] [NVPTX] Add `-march=general` option to mirror default configuration (PR #85222)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Yichen Yan (oraluben)

<details>
<summary>Changes</summary>

This PR adds `-march=generic` support for the NVPTX backend. This fulfills a TODO introduced in #<!-- -->79873.

With this PR, users can explicitly request the default CUDA architecture. This default is regularly updated, and the most recent configuration as of commit ab202aa sets it to `sm_52`. This value is also assumed when no `-march` option is provided.

This PR does not address any compatibility issues between different CUDA versions.


---
Full diff: https://github.com/llvm/llvm-project/pull/85222.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/Cuda.cpp (+2-2) 
- (modified) clang/test/Driver/cuda-cross-compiling.c (+7-2) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index c6007d3cfab864..4cb98f9f28963c 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -750,8 +750,8 @@ NVPTXToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
     if (!llvm::is_contained(*DAL, A))
       DAL->append(A);
 
-  // TODO: We should accept 'generic' as a valid architecture.
-  if (!DAL->hasArg(options::OPT_march_EQ) && OffloadKind != Action::OFK_None) {
+  if ((!DAL->hasArg(options::OPT_march_EQ) && OffloadKind != Action::OFK_None) ||
+      (DAL->getLastArgValue(options::OPT_march_EQ) == "generic")) {
     DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_march_EQ),
                       CudaArchToString(CudaArch::CudaDefault));
   } else if (DAL->getLastArgValue(options::OPT_march_EQ) == "native") {
diff --git a/clang/test/Driver/cuda-cross-compiling.c b/clang/test/Driver/cuda-cross-compiling.c
index 086840accebe7f..e5aeca8300f85c 100644
--- a/clang/test/Driver/cuda-cross-compiling.c
+++ b/clang/test/Driver/cuda-cross-compiling.c
@@ -32,10 +32,15 @@
 //
 // RUN: %clang -target nvptx64-nvidia-cuda -march=sm_61 -### %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=ARGS %s
+// RUN: %clang -target nvptx64-nvidia-cuda -march=generic -### %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=GENERIC %s
 
 //      ARGS: -cc1" "-triple" "nvptx64-nvidia-cuda" "-S" {{.*}} "-target-cpu" "sm_61" "-target-feature" "+ptx{{[0-9]+}}" {{.*}} "-o" "[[PTX:.+]].s"
 // ARGS-NEXT: ptxas{{.*}}"-m64" "-O0" "--gpu-name" "sm_61" "--output-file" "[[CUBIN:.+]].cubin" "[[PTX]].s" "-c"
 // ARGS-NEXT: nvlink{{.*}}"-o" "a.out" "-arch" "sm_61" {{.*}} "[[CUBIN]].cubin"
+//      GENERIC: -cc1" "-triple" "nvptx64-nvidia-cuda" "-S" {{.*}} "-target-cpu" "sm_52" "-target-feature" "+ptx{{[0-9]+}}" {{.*}} "-o" "[[PTX:.+]].s"
+// GENERIC-NEXT: ptxas{{.*}}"-m64" "-O0" "--gpu-name" "sm_52" "--output-file" "[[CUBIN:.+]].cubin" "[[PTX]].s" "-c"
+// GENERIC-NEXT: nvlink{{.*}}"-o" "a.out" "-arch" "sm_52" {{.*}} "[[CUBIN]].cubin"
 
 //
 // Test the generated arguments to the CUDA binary utils when targeting NVPTX. 
@@ -85,6 +90,6 @@
 // MISSING: error: Must pass in an explicit nvptx64 gpu architecture to 'nvlink'
 
 // RUN: %clang -target nvptx64-nvidia-cuda -flto -c %s -### 2>&1 \
-// RUN:   | FileCheck -check-prefix=GENERIC %s
+// RUN:   | FileCheck -check-prefix=COMPILE %s
 
-// GENERIC-NOT: -cc1" "-triple" "nvptx64-nvidia-cuda" {{.*}} "-target-cpu"
+// COMPILE-NOT: -cc1" "-triple" "nvptx64-nvidia-cuda" {{.*}} "-target-cpu"

``````````

</details>


https://github.com/llvm/llvm-project/pull/85222