[SystemZ] Enable AtomicExpand pass #70398
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Thanks, this looks good to me. Could you also add test cases for the newly-supported operations? Along the lines of the existing tests in llvm/test/CodeGen/SystemZ/atomicrmw-*, but for fadd/fsub/fmin/fmax and potentially uinc_wrap/udec_wrap. Also, maybe add variants of the atomic-load/store-* and atomicrmw-xchg-* tests for floating-point types. |
The upcoming OpenMP support for SystemZ requires handling of IR insns like `atomicrmw fadd`. Normally atomic float operations are expanded by Clang and such insns do not occur, but OpenMP generates them directly. Other architectures handle this using the AtomicExpand pass, which SystemZ did not need so far. Enable it; implement atomicrmw sub-operations uinc_wrap and udec_wrap by expanding them to a compare-and-swap loop; add tests. Currently AtomicExpand treats atomic load and stores of floats pessimistically: it casts them to integers, which SystemZ does not need, since the floating point load and store instructions are already atomic. However, the way Clang currently expands them is pessimistic as well, so this change does not make things worse. Optimizing operations on atomic floats can be a separate change in the future. This change does not create any differences the Linux kernel build.
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uweigand
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Oct 31, 2023
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The upcoming OpenMP support for SystemZ requires handling of IR insns like
atomicrmw fadd. Normally atomic float operations are expanded by Clang and such insns do not occur, but OpenMP generates them directly. Other architectures handle this using the AtomicExpand pass, which SystemZ did not need so far. Enable it.Currently AtomicExpand treats atomic load and stores of floats pessimistically: it casts them to integers, which SystemZ does not need, since the floating point load and store instructions are already atomic. However, the way Clang currently expands them is pessimistic as well, so this change does not make things worse. Optimizing operations on atomic floats can be a separate change in the future.
This change does not create any differences the Linux kernel build.