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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
[`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
## 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
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
suggestion by @eddyb).
## Generic types and structures
### Generic types and structures
@irinagpopa started to parametrize the types of `rustc_codegen_llvm` by a
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
backend's context.
## Traits and interface
### Traits and interface
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.
@ -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
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 best solution since LLVM has a very special way of doing things: when