[clang] [Clang] Make `-Xarch_` handling generic for all toolchains (PR #125421)

[Artem Belevich via cfe-commits]

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+// RUN: %clang -x cuda %s -Xarch_nvptx64 -O3 -S -nogpulib -nogpuinc -### 2>&1 | FileCheck -check-prefix=O3ONCE %s
+// RUN: %clang -x cuda %s -Xarch_device -O3 -S -nogpulib -nogpuinc -### 2>&1 | FileCheck -check-prefix=O3ONCE %s
+// RUN: %clang -x hip %s -Xarch_amdgcn -O3 -S -nogpulib -nogpuinc -### 2>&1 | FileCheck -check-prefix=O3ONCE %s
+// RUN: %clang -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -nogpulib -nogpuinc \
+// RUN:   -Xarch_amdgcn -march=gfx90a -Xarch_amdgcn -O3 -S -### %s 2>&1 \
+// RUN: | FileCheck -check-prefix=O3ONCE %s
+// RUN: %clang -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -nogpulib -nogpuinc \
+// RUN:   -Xarch_nvptx64 -march=sm_52 -Xarch_nvptx64 -O3 -S -### %s 2>&1 \
+// RUN: | FileCheck -check-prefix=O3ONCE %s
+// O3ONCE: "-O3"
+// O3ONCE-NOT: "-O3"
+
+// RUN: %clang -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda,amdgcn-amd-amdhsa -nogpulib \
+// RUN:   --target=x86_64-unknown-linux-gnu -Xarch_nvptx64 --offload-arch=sm_52,sm_60 -nogpuinc \
+// RUN:   -Xarch_amdgcn --offload-arch=gfx90a,gfx1030 -ccc-print-bindings -### %s 2>&1 \
+// RUN: | FileCheck -check-prefix=OPENMP %s
+//
+// OPENMP: # "x86_64-unknown-linux-gnu" - "clang", inputs: ["[[INPUT:.+]]"], output: "[[HOST_BC:.+]]"
+// OPENMP: # "amdgcn-amd-amdhsa" - "clang", inputs: ["[[INPUT]]", "[[HOST_BC]]"], output: "[[GFX1030_BC:.+]]"
+// OPENMP: # "amdgcn-amd-amdhsa" - "clang", inputs: ["[[INPUT]]", "[[HOST_BC]]"], output: "[[GFX90A_BC:.+]]"
+// OPENMP: # "nvptx64-nvidia-cuda" - "clang", inputs: ["[[INPUT]]", "[[HOST_BC]]"], output: "[[SM52_PTX:.+]]"
+// OPENMP: # "nvptx64-nvidia-cuda" - "NVPTX::Assembler", inputs: ["[[SM52_PTX]]"], output: "[[SM52_CUBIN:.+]]"
+// OPENMP: # "nvptx64-nvidia-cuda" - "clang", inputs: ["[[INPUT]]", "[[HOST_BC]]"], output: "[[SM60_PTX:.+]]"
+// OPENMP: # "nvptx64-nvidia-cuda" - "NVPTX::Assembler", inputs: ["[[SM60_PTX]]"], output: "[[SM60_CUBIN:.+]]"
+// OPENMP: # "x86_64-unknown-linux-gnu" - "Offload::Packager", inputs: ["[[GFX1030_BC]]", "[[GFX90A_BC]]", "[[SM52_CUBIN]]", "[[SM60_CUBIN]]"], output: "[[BINARY:.+]]"
+// OPENMP: # "x86_64-unknown-linux-gnu" - "clang", inputs: ["[[HOST_BC]]", "[[BINARY]]"], output: "[[HOST_OBJ:.+]]"
+// OPENMP: # "x86_64-unknown-linux-gnu" - "Offload::Linker", inputs: ["[[HOST_OBJ]]"], output: "a.out"
+
+// RUN: %clang -x cuda %s --offload-arch=sm_52,sm_60 -Xarch_sm_52 -O3 -Xarch_sm_60 -O0 \
+// RUN:   --target=x86_64-unknown-linux-gnu -Xarch_host -O3 -S -nogpulib -nogpuinc -### 2>&1 \
+// RUN: | FileCheck -check-prefix=CUDA %s
+// CUDA: "-cc1" "-triple" "nvptx64-nvidia-cuda" {{.*}}"-target-cpu" "sm_52" {{.*}}"-O3"
+// CUDA: "-cc1" "-triple" "nvptx64-nvidia-cuda" {{.*}}"-target-cpu" "sm_60" {{.*}}"-O0"
+// CUDA: "-cc1" "-triple" "x86_64-unknown-linux-gnu" {{.*}}"-O3"
+
+// RUN: %clang -x cuda %s -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda \
+// RUN:   -Xarch_sm_52 --offload-arch=sm_52 -S -nogpulib -nogpuinc -### 2>&1 \
+// RUN: | FileCheck -check-prefix=SPECIFIC %s
+// SPECIFIC: "-cc1" "-triple" "nvptx64-nvidia-cuda" {{.*}}"-target-cpu" "sm_52"
----------------
Artem-B wrote:

It all seems to boil down to "what does Xarch mean". The conventional `-X<something>` model is "pass the arg to <something> in the compilation pipeline". You seem to propose that for openMP it will be "use it to construct compiler pipeline". Not sure I like this dichotomy where we commingling pipeline construction with tweaking of already constructed pipeline.

Perhaps a cleaner way would be to figure out a better way tof OpenMP to set up the build pipeline structure (that's what --offload-arch is for), and keep `Xarch` exclusively as a way to tweak the options for the already constructed pipeline.
Presumably OpenMP already has the ways to specify the desired offloading targets.  `Xarch` does not look like the right tool for that job. It can do it, but it opens a can of corner cases.

If openMP does not have a viable better way to configure the compilation pipeline, we could make `-Xarch=backend. --offload-arch=target` a documented special case for OpenMP only. I would strongly prefer to keep CUDA/HIP to continue diagnosing `--offload-arch` being passed to `cc1`.

https://github.com/llvm/llvm-project/pull/125421