Update memory.md

src/memory.md

@@ -1,8 +1,8 @@
 # Memory Management in Rustc
 
-Rustc tries to be pretty careful how it manages memory. The compiler allocates
-_a lot_ of data structures throughout compilation, and if we are not careful,
-it will take a lot of time and space to do so.
+Generally rustc tries to be pretty careful how it manages memory.
+The compiler allocates _a lot_ of data structures throughout compilation,
+and if we are not careful, it will take a lot of time and space to do so.
 
 One of the main way the compiler manages this is using [arena]s and [interning].
 
@@ -11,16 +11,18 @@ One of the main way the compiler manages this is using [arena]s and [interning].
 
 ## Arenas and  Interning
 
-We create a LOT of data structures during compilation. For performance reasons,
-we allocate them from a global memory pool; they are each allocated once from a
-long-lived *arena*. This is called _arena allocation_. This system reduces
-allocations/deallocations of memory. It also allows for easy comparison of
-types for equality: for each interned type `X`, we implemented [`PartialEq for
-X`][peqimpl], so we can just compare pointers. The [`CtxtInterners`] type
-contains a bunch of maps of interned types and the arena itself.
+Since A LOT of data structures are created during compilation, for performance
+reasons, we allocate them from a global memory pool.
+Each are allocated once from a long-lived *arena*.
+This is called _arena allocation_.
+This system reduces allocations/deallocations of memory.
+It also allows for easy comparison of types (more on types [here](./ty.md)) for equality:
+for each interned type `X`, we implemented [`PartialEq` for X][peqimpl],
+so we can just compare pointers.
+The [`CtxtInterners`] type contains a bunch of maps of interned types and the arena itself.
 
-[peqimpl]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html#implementations
 [`CtxtInterners`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.CtxtInterners.html#structfield.arena
+[peqimpl]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html#implementations
 
 ### Example: `ty::TyKind`
 
@@ -30,7 +32,7 @@ compiler doesn’t naively allocate from the buffer.  Instead, we check if that
 type was already constructed. If it was, we just get the same pointer we had
 before, otherwise we make a fresh pointer. With this schema if we want to know
 if two types are the same, all we need to do is compare the pointers which is
-efficient. `TyKind` should never be constructed on the stack, and it would be unusable
+efficient. [`TyKind`] should never be constructed on the stack, and it would be unusable
 if done so.
 You always allocate them from this arena and you always intern them so they are
 unique.
@@ -43,26 +45,33 @@ to that buffer is freed and our `'tcx` references would be invalid.
 In addition to types, there are a number of other arena-allocated data structures that you can
 allocate, and which are found in this module. Here are a few examples:
 
-- [`GenericArgs`], allocated with `mk_args` – this will intern a slice of types, often used
+- [`GenericArgs`], allocated with [`mk_args`] – this will intern a slice of types, often used
 to specify the values to be substituted for generics args (e.g. `HashMap<i32, u32>` would be
 represented as a slice `&'tcx [tcx.types.i32, tcx.types.u32]`).
 - [`TraitRef`], typically passed by value – a **trait reference** consists of a reference to a trait
   along with its various type parameters (including `Self`), like `i32: Display` (here, the def-id
   would reference the `Display` trait, and the args would contain `i32`). Note that `def-id` is
   defined and discussed in depth in the [`AdtDef and DefId`][adtdefid] section.
-- [`Predicate`] defines something the trait system has to prove (see `traits` module).
+- [`Predicate`] defines something the trait system has to prove (see [traits] module).
 
 [`GenericArgs`]: ./ty_module/generic_arguments.md#the-genericargs-type
 [adtdefid]: ./ty_module/generic_arguments.md#adtdef-and-defid
 [`TraitRef`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/type.TraitRef.html
+[`AdtDef` and `DefId`]: ./ty.md#adts-representation
+[`def-id`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def_id/struct.DefId.html
+[`GenericArgs`]: ./generic_arguments.html#GenericArgs
+[`mk_args`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html#method.mk_args
+[adtdefid]: ./ty_module/generic_arguments.md#adtdef-and-defid
 [`Predicate`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Predicate.html
-
+[`TraitRef`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TraitRef.html
 [`ty::TyKind`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/sty/type.TyKind.html
+[`TyKind`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/ty_kind/enum.TyKind.html
+[traits]: ./traits/resolution.md
 
-## The tcx and how it uses lifetimes
+## The `tcx` and how it uses lifetimes
 
-The `tcx` ("typing context") is the central data structure in the compiler. It is the context that
-you use to perform all manner of queries. The struct `TyCtxt` defines a reference to this shared
+The typing context (`tcx`) is the central data structure in the compiler. It is the context that
+you use to perform all manner of queries. The `struct` [`TyCtxt`] defines a reference to this shared
 context:
 
 ```rust,ignore
@@ -76,10 +85,13 @@ As you can see, the `TyCtxt` type takes a lifetime parameter. When you see a ref
 lifetime like `'tcx`, you know that it refers to arena-allocated data (or data that lives as long as
 the arenas, anyhow).
 
+[`TyCtxt`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html
+
 ### A Note On Lifetimes
 
 The Rust compiler is a fairly large program containing lots of big data
-structures (e.g. the AST, HIR, and the type system) and as such, arenas and
+structures (e.g. the [Abstract Syntax Tree (AST)][ast], [High-Level Intermediate
+Representation (`HIR`)][hir], and the type system) and as such, arenas and
 references are heavily relied upon to minimize unnecessary memory use. This
 manifests itself in the way people can plug into the compiler (i.e. the
 [driver](./rustc-driver.md)), preferring a "push"-style API (callbacks) instead
@@ -90,4 +102,6 @@ duplication while also preventing a lot of the ergonomic issues due to many
 pervasive lifetimes. The [`rustc_middle::ty::tls`][tls] module is used to access these
 thread-locals, although you should rarely need to touch it.
 
+[ast]: ./ast-validation.md
+[hir]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/index.html
 [tls]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/tls/index.html