[llvm-dev] Use Global ISel or SelectionDAG (original) (raw)

Luís Marques via llvm-dev llvm-dev at lists.llvm.org
Thu Feb 13 14:51:47 PST 2020

Hi Floris,

For a bachelor thesis I would probably recommend going with the safest choice of SelectionDAG. When I started doing LLVM development I was surprised by how common it is to have to solve LLVM issues that other architectures didn't happen to run into, despite me working on a very conventional target arch (RISC-V). You don't want to spend all your time budget on incidental problems that aren't core to your thesis. That said, GlobalISel is cool, so if you can make it work for you... ¯_(ツ)_/¯

Alex Bradbury did some great work on creating a series of patches that show how to create the RISC-V target in a piecemeal and systematic way, so you might want to check that out:

https://github.com/lowRISC/riscv-llvm https://github.com/lowRISC/riscv-llvm/tree/master/docs

Cheers, Luis

On Thu, Feb 13, 2020 at 10:08 PM floris westermann via llvm-dev < llvm-dev at lists.llvm.org> wrote:

Hi llvm-dev,

I am currently writing a backend for an architecture I am designing in my bachelor's thesis and recently came across the GlobalISel Selection Framework. Should already start using this over the more common Selection DAG? Being new llvm backend development, I am not sure if GlobalISel would be "easier" to implement than ISelDAG and if there is any decent documentation on how to do so. Cheers, Floris

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