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Explain what the rest of the backend agnostic page is about

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Noah Lev 2023-02-17 13:43:13 -08:00 committed by Tshepang Mbambo
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@ -10,10 +10,13 @@ namely LLVM, [Cranelift], and [GCC].
[GCC]: https://github.com/rust-lang/rustc_codegen_gcc [GCC]: https://github.com/rust-lang/rustc_codegen_gcc
[`rustc_codegen_ssa`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/index.html [`rustc_codegen_ssa`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/index.html
# Refactoring of `rustc_codegen_llvm` Below is some background information on the refactoring that created this
abstract interface.
## Refactoring of `rustc_codegen_llvm`
by Denis Merigoux, October 23rd 2018 by Denis Merigoux, October 23rd 2018
## State of the code before the refactoring ### State of the code before the refactoring
All the code related to the compilation of MIR into LLVM IR was contained All the code related to the compilation of MIR into LLVM IR was contained
inside the `rustc_codegen_llvm` crate. Here is the breakdown of the most inside the `rustc_codegen_llvm` crate. Here is the breakdown of the most
@ -53,7 +56,7 @@ While the LLVM-specific code will be left in `rustc_codegen_llvm`, all the new
traits and backend-agnostic code will be moved in `rustc_codegen_ssa` (name traits and backend-agnostic code will be moved in `rustc_codegen_ssa` (name
suggestion by @eddyb). suggestion by @eddyb).
## Generic types and structures ### Generic types and structures
@irinagpopa started to parametrize the types of `rustc_codegen_llvm` by a @irinagpopa started to parametrize the types of `rustc_codegen_llvm` by a
generic `Value` type, implemented in LLVM by a reference `&'ll Value`. This generic `Value` type, implemented in LLVM by a reference `&'ll Value`. This
@ -105,7 +108,7 @@ of the backend and it makes more sense to leave their definition to the backend
implementor than to allow just a narrow spot via a generic field for the implementor than to allow just a narrow spot via a generic field for the
backend's context. backend's context.
## Traits and interface ### Traits and interface
Because they have to be defined by the backend, `CodegenCx` and `Builder` will Because they have to be defined by the backend, `CodegenCx` and `Builder` will
be the structures implementing all the traits defining the backend's interface. be the structures implementing all the traits defining the backend's interface.
@ -172,7 +175,7 @@ called. However, when implementing a Rust backend for `rustc`, these methods
will need information from `CodegenCx`, hence the additional parameter (unused will need information from `CodegenCx`, hence the additional parameter (unused
in the LLVM implementation of the trait). in the LLVM implementation of the trait).
## State of the code after the refactoring ### State of the code after the refactoring
The traits offer an API which is very similar to the API of LLVM. This is not The traits offer an API which is very similar to the API of LLVM. This is not
the best solution since LLVM has a very special way of doing things: when the best solution since LLVM has a very special way of doing things: when