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The new interfaces provide getters and setters for the weight information about the branches of BranchOpInterface and RegionBranchOpInterface operations. These interfaces are done the same way as LLVM dialect's BranchWeightOpInterface. The plan is to produce this information in Flang, e.g. mark most probably "cold" code as such and allow LLVM to order basic blocks accordingly. An example of such a code is copy loops generated for arrays repacking - we can mark it as "cold" assuming that the copy will not happen dynamically. If the copy actually happens the overhead of the copy is probably high enough so that we may not care about the little overhead of jumping to the "cold" code and fetching it.
Multi-Level Intermediate Representation
See https://mlir.llvm.org/ for more information.