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Add in memory object files support to CompiledModule and ArchiveBuilder #69946
Description
Activity
Aside: LLVM also supports emitting object files into memory (just pass a
raw_string_ostreaminstead of araw_fd_ostream), so if this feature gets implemented for cranelift codegen and helps there, it might help LLVM codegen too.Reacted by bjorn3We may want to only do this when the total size of all codegen units is below a certain threshold to reduce max-rss for big crates like
scriptandrustc. (Assuming that LLVM performs the archive building in a streaming way like cg_clif.)
https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/struct.CompiledModule.html
https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/back/archive/trait.ArchiveBuilder.html
rustc_codegen_cranelift can emit object files to memory without writing them to the disk. With the current setup they need to be written to the disk before an rlib can be created. This doubles the amount of data written to the disk compared to emitting the object files to memory and then creating an rlib file from that. Linking a dylib or executable will still need to write the object files to the disk, but at least rlibs don't have to anymore.