| Issue |
71223
|
| Summary |
[CUDA][HIP] fails to compile __int128 division
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
yxsamliu
|
Currently clang is able to lower `__int128` add/subtract/multiply operations in nvptx and amgpu. However, it lowers `__int128` division to compiler-rt lib call `__divti3`. Currently compiler-rt does not supports nvptx or amgpu target. Even if it does, amdgpu backend does not support ISA level linking, therefore is unable to link compiler-rt after LLVM codegen.
failure on amdgpu: https://godbolt.org/z/4oqPoYGG9
failure on nvptx: https://godbolt.org/z/411M3x4Eh
`__int128` division on x86_4 showing lowering to `__divti3` https://godbolt.org/z/b793fE7E5
`__int128` division with nvcc: https://godbolt.org/z/7WaM7vG9j
compiler-rt implementation of 128 bit integer division: https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/builtins/int_div_impl.inc
Ideally, nvptx and amdgpu backend should support ISA level linking and compiler-rt. However, that might take some time.
Another option is to let llvm lower `__int128` division to instructions instead of libcall (https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp#L4398). However, this may not worth the effort.
Another option is to implement `__divti3` as a inline function in the default clang header for CUDA/HIP. If `__int128` division is found in device code, mark it as used. This seems to be a feasible solution.
@Artem-B
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