obey rust-lang#1132

Author: tshepang

src/part-5-intro.md

@@ -1,43 +1,48 @@
 # From MIR to Binaries
 
-All of the preceding chapters of this guide have one thing in common: we never
-generated any executable machine code at all! With this chapter, all of that
-changes.
+All of the preceding chapters of this guide have one thing in common:
+we never generated any executable machine code at all!
+With this chapter, all of that changes.
 
-So far, we've shown how the compiler can take raw source code in text format
-and transform it into [MIR]. We have also shown how the compiler does various
-analyses on the code to detect things like type or lifetime errors. Now, we
-will finally take the MIR and produce some executable machine code.
+So far,
+we've shown how the compiler can take raw source code in text format
+and transform it into [MIR].
+We have also shown how the compiler does various
+analyses on the code to detect things like type or lifetime errors.
+Now, we will finally take the MIR and produce some executable machine code.
 
 [MIR]: ./mir/index.md
 
-> NOTE: This part of a compiler is often called the _backend_. The term is a bit
-> overloaded because in the compiler source, it usually refers to the "codegen
-> backend" (i.e. LLVM, Cranelift, or GCC). Usually, when you see the word "backend"
-> in this part, we are referring to the "codegen backend".
+> NOTE: This part of a compiler is often called the _backend_.
+> The term is a bit overloaded because in the compiler source,
+> it usually refers to the "codegen backend" (i.e. LLVM, Cranelift, or GCC).
+> Usually, when you see the word "backend"  in this part,
+> we are referring to the "codegen backend".
 
 So what do we need to do?
 
-0. First, we need to collect the set of things to generate code for. In
-   particular, we need to find out which concrete types to substitute for
-   generic ones, since we need to generate code for the concrete types.
-   Generating code for the concrete types (i.e. emitting a copy of the code for
-   each concrete type) is called _monomorphization_, so the process of
-   collecting all the concrete types is called _monomorphization collection_.
+0. First, we need to collect the set of things to generate code for.
+   In particular,
+   we need to find out which concrete types to substitute for generic ones,
+   since we need to generate code for the concrete types.
+   Generating code for the concrete types
+   (i.e. emitting a copy of the code for each concrete type) is called _monomorphization_,
+   so the process of collecting all the concrete types is called _monomorphization collection_.
 1. Next, we need to actually lower the MIR to a codegen IR
    (usually LLVM IR) for each concrete type we collected.
-2. Finally, we need to invoke the codegen backend, which runs a bunch of
-   optimization passes, generates executable code, and links together an
-   executable binary.
+2. Finally, we need to invoke the codegen backend,
+   which runs a bunch of optimization passes,
+   generates executable code,
+   and links together an executable binary.
 
 [codegen1]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/base/fn.codegen_crate.html
 
 The code for codegen is actually a bit complex due to a few factors:
 
-- Support for multiple codegen backends (LLVM, Cranelift, and GCC). We try to share as much
-  backend code between them as possible, so a lot of it is generic over the
-  codegen implementation. This means that there are often a lot of layers of
-  abstraction.
+- Support for multiple codegen backends (LLVM, Cranelift, and GCC).
+  We try to share as much backend code between them as possible,
+  so a lot of it is generic over the codegen implementation.
+  This means that there are often a lot of layers of abstraction.
 - Codegen happens asynchronously in another thread for performance.
 - The actual codegen is done by a third-party library (either of the 3 backends).
 
@@ -48,5 +53,5 @@ while the [`rustc_codegen_llvm`][llvm] crate contains code specific to LLVM code
 [llvm]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_llvm/index.html
 
 At a very high level, the entry point is
-[`rustc_codegen_ssa::base::codegen_crate`][codegen1]. This function starts the
-process discussed in the rest of this chapter.
+[`rustc_codegen_ssa::base::codegen_crate`][codegen1].
+This function starts the process discussed in the rest of this chapter.