Choose target ISA in `@code_llvm` and `@code_native` about julia HOT 12 OPEN

It'd be nice to have pointers of where one would need to look at, in case they were interested in tackling the issue

So code_native/code_llvm use jl_get_llvmf_defn which takes in CodegenParams.

In NewPM PM{jl_ExecutionEngine->cloneTargetMachine(), getOptLevel(jl_options.opt_level)}; we setup a new passmanager based on the global TargetMachine.

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So first thing I would do is familiarize myself with the chain from code_llvm to jl_get_llvmf_defn_impl and understand how these functions work, because it's those that you will be modifying

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I'm not even sure that the ISAs need to be smaller, we should never execute this code. In essence one would need to pass the features to the LLVM module we codegen into.

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Oh, that'd be lovely as we wouldn't depend on the current host, that was a limitation mentioned by @vchuravy on slack.

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That limitation only applies to -C

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Ah, I got mixed up about it then!

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Thanks! Just to check if I understood correctly, one strategy to accomplish this is to add a field to jl_cgparams_t and CodegenParams for the target, which by default would represent the current target, but could optionally be a different ISA, and that'd be used in jl_get_llvmf_defn_impl to create a passmanager for the desired target (handling error cases)?

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Yeah that's what I would try.

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Thanks! I added the "good fist issue" label, sounds like a fun task for someone who wants to get started with the compiler 🙂

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Only for dump_module=true though. With that flag, we can print code for pretty much any combination of compiler options, pipelines, params, CPUs and target architectures. With dump_module=false though, we can strictly only print (dis)assembly for the native machine with all of the vanilla options.

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Hey team @gbaraldi @giordano @vtjnash @vtjnash .I am beginner to open source.I want to take this issue .Can you please guide me,may with some doc for above issue.

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Ohk sure @gbaraldi ,
I will go through code_llvm to jl_get_llvmf_defn_impl to gain a thorough understanding.

Thankyou.

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