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  • Johannes Doerfert's avatar
    [OpenMP] Prototype opt-in new GPU device RTL · 67ab875f
    Johannes Doerfert authored
    The "old" OpenMP GPU device runtime (D14254) has served us well for many
    years but modernizing it has caused some pain recently. This patch
    introduces an alternative which is mostly written from scratch embracing
    OpenMP 5.X, C++, LLVM coding style (where applicable), and conceptual
    interfaces. This new runtime is opt-in through a clang flag (D106793).
    The new runtime is currently only build for nvptx and has "-new" in its
    name.
    
    The design is tailored towards middle-end optimizations rather than
    front-end code generation choices, a trend we already started in the old
    runtime a while back. In contrast to the old one, state is organized in
    a simple manner rather than a "smart" one. While this can induce costs
    it helps optimizations. Our expectation is that the majority of codes
    can be optimized and a "simple" design is therefore preferable. The new
    runtime does also avoid users to pay for things they do not use,
    especially wrt. memory. The unlikely case of nested parallelism is
    supported but costly to make the more likely case use less resources.
    
    The worksharing and reduction implementation have been taken from the
    old runtime and will be rewritten in the future if necessary.
    
    Documentation and debug features are still mostly missing and will be
    added over time.
    
    All external symbols start with `__kmpc` for legacy reasons but should
    be renamed once we switch over to a single runtime. All internal symbols
    are placed in appropriate namespaces (anonymous or `_OMP`) to avoid name
    clashes with user symbols.
    
    Differential Revision: https://reviews.llvm.org/D106803
    67ab875f
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