Encode type-/layout- vs. region-based alias info separately in LLVM IR
#54 395 ouverte le 7 mai 2024
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Description
Currently we redundantly encode region information in both !tbaa and !alias.scope metadata for LLVM.
We'd like to separate these so that TBAA is only used to encode the layout-/type-based non-aliasing information, and !alias.scope is used just for the region-based information.
For reference, here's the existing TBAA hierarchy: https://github.com/JuliaLang/julia/blob/5f7bfc0a8374a902b723870262ffe7ddfbc44e77/src/codegen.cpp#L351-L375
The first step is probably to (1) re-factor the code to stop using ::fromTBAA. Instead, the region information should be passed around as a separate piece of aliasing-related information. Most likely that means creating a jl_aliasinfo_t much earlier, and updating jl_cgval_t to carry it instead of just TBAA metadata. Then, (2) remove tbaa_gcframe, tbaa_stack, tbaa_const, and tbaa_data from the TBAA hierarchy.
Afterwards, an excellent follow-up will be to expand the TBAA hierarchy to encode a much broader set of types into it, including ideally user-defined structs.