Our existing instruction selection framework, SelectionDAGISel (SDISel), has some fundamental limitations, including, but not limited to, slow compile time, basic block only scope, and monolithic approach. Over the years, we spent a lot of effort to workaround these limitations with more target hooks and more optimizations passes (e.g., CodeGenPrepare, ConstantHoisting) with their own problems (inaccurate heuristic, have to predict what the instruction selector will do, etc.) and limitations.
We believe that it is time to come up with a new instruction selection framework, global-isel, that will solve these problems while offering new opportunities to improve our code generation. In this talk, we will present our plan to bring global-isel to LLVM.
