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| <h1 id="overview-of-the-compiler"><a class="header" href="#overview-of-the-compiler">Overview of the compiler</a></h1> |
| <p>This chapter is about the overall process of compiling a program – how |
| everything fits together.</p> |
| <p>The Rust compiler is special in two ways: it does things to your code that |
| other compilers don’t do (e.g. borrow-checking) and it has a lot of |
| unconventional implementation choices (e.g. queries). We will talk about these |
| in turn in this chapter, and in the rest of the guide, we will look at the |
| individual pieces in more detail.</p> |
| <h2 id="what-the-compiler-does-to-your-code"><a class="header" href="#what-the-compiler-does-to-your-code">What the compiler does to your code</a></h2> |
| <p>So first, let’s look at what the compiler does to your code. For now, we will |
| avoid mentioning how the compiler implements these steps except as needed.</p> |
| <h3 id="invocation"><a class="header" href="#invocation">Invocation</a></h3> |
| <p>Compilation begins when a user writes a Rust source program in text and invokes |
| the <code>rustc</code> compiler on it. The work that the compiler needs to perform is |
| defined by command-line options. For example, it is possible to enable nightly |
| features (<code>-Z</code> flags), perform <code>check</code>-only builds, or emit the LLVM |
| Intermediate Representation (<code>LLVM-IR</code>) rather than executable machine code. |
| The <code>rustc</code> executable call may be indirect through the use of <code>cargo</code>.</p> |
| <p>Command line argument parsing occurs in the <a href="rustc-driver/intro.html"><code>rustc_driver</code></a>. This crate |
| defines the compile configuration that is requested by the user and passes it |
| to the rest of the compilation process as a <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/interface/struct.Config.html"><code>rustc_interface::Config</code></a>.</p> |
| <h3 id="lexing-and-parsing"><a class="header" href="#lexing-and-parsing">Lexing and parsing</a></h3> |
| <p>The raw Rust source text is analyzed by a low-level <em>lexer</em> located in |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lexer/index.html"><code>rustc_lexer</code></a>. At this stage, the source text is turned into a stream of |
| atomic source code units known as <em>tokens</em>. The <code>lexer</code> supports the |
| Unicode character encoding.</p> |
| <p>The token stream passes through a higher-level lexer located in |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html"><code>rustc_parse</code></a> to prepare for the next stage of the compile process. The |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.Lexer.html"><code>Lexer</code></a> <code>struct</code> is used at this stage to perform a set of validations |
| and turn strings into interned symbols (<em>interning</em> is discussed later). |
| <a href="https://en.wikipedia.org/wiki/String_interning">String interning</a> is a way of storing only one immutable |
| copy of each distinct string value.</p> |
| <p>The lexer has a small interface and doesn’t depend directly on the diagnostic |
| infrastructure in <code>rustc</code>. Instead it provides diagnostics as plain data which |
| are emitted in <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/index.html"><code>rustc_parse::lexer</code></a> as real diagnostics. The <code>lexer</code> |
| preserves full fidelity information for both IDEs and procedural macros |
| (sometimes referred to as “proc-macros”).</p> |
| <p>The <em>parser</em> <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html">translates the token stream from the <code>lexer</code> into an Abstract Syntax |
| Tree (AST)</a>. It uses a recursive descent (top-down) approach to syntax |
| analysis. The crate entry points for the <code>parser</code> are the |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.parse_crate_mod"><code>Parser::parse_crate_mod()</code></a> and <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.parse_mod"><code>Parser::parse_mod()</code></a> |
| methods found in <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html"><code>rustc_parse::parser::Parser</code></a>. The external module parsing |
| entry point is <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_expand/module/fn.parse_external_mod.html"><code>rustc_expand::module::parse_external_mod</code></a>. |
| And the macro-<code>parser</code> entry point is <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.parse_nonterminal"><code>Parser::parse_nonterminal()</code></a>.</p> |
| <p>Parsing is performed with a set of <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html"><code>parser</code></a> utility methods including <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.bump"><code>bump</code></a>, |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.check"><code>check</code></a>, <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.eat"><code>eat</code></a>, <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.expect"><code>expect</code></a>, <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.look_ahead"><code>look_ahead</code></a>.</p> |
| <p>Parsing is organized by semantic construct. Separate |
| <code>parse_*</code> methods can be found in the <a href="https://github.com/rust-lang/rust/tree/HEAD/compiler/rustc_parse/src/parser"><code>rustc_parse</code></a> |
| directory. The source file name follows the construct name. For example, the |
| following files are found in the <code>parser</code>:</p> |
| <ul> |
| <li><a href="https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_parse/src/parser/expr.rs"><code>expr.rs</code></a></li> |
| <li><a href="https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_parse/src/parser/pat.rs"><code>pat.rs</code></a></li> |
| <li><a href="https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_parse/src/parser/ty.rs"><code>ty.rs</code></a></li> |
| <li><a href="https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_parse/src/parser/stmt.rs"><code>stmt.rs</code></a></li> |
| </ul> |
| <p>This naming scheme is used across many compiler stages. You will find either a |
| file or directory with the same name across the parsing, lowering, type |
| checking, <a href="./thir.html">Typed High-level Intermediate Representation (<code>THIR</code>)</a> lowering, and |
| <a href="mir/index.html">Mid-level Intermediate Representation (<code>MIR</code>)</a> building sources.</p> |
| <p>Macro-expansion, <code>AST</code>-validation, name-resolution, and early linting also take |
| place during the lexing and parsing stage.</p> |
| <p>The <a href="https://doc.rust-lang.org/beta/nightly-rustc/rustc_ast/index.html"><code>rustc_ast::ast</code></a>::{<a href="https://doc.rust-lang.org/beta/nightly-rustc/rustc_ast/ast/struct.Crate.html"><code>Crate</code></a>, <a href="https://doc.rust-lang.org/beta/nightly-rustc/rustc_ast/ast/struct.Expr.html"><code>Expr</code></a>, <a href="https://doc.rust-lang.org/beta/nightly-rustc/rustc_ast/ast/struct.Pat.html"><code>Pat</code></a>, …} <code>AST</code> nodes are |
| returned from the parser while the standard <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html"><code>Diag</code></a> API is used |
| for error handling. Generally Rust’s compiler will try to recover from errors |
| by parsing a superset of Rust’s grammar, while also emitting an error type.</p> |
| <h3 id="ast-lowering"><a class="header" href="#ast-lowering"><code>AST</code> lowering</a></h3> |
| <p>Next the <code>AST</code> is converted into <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/index.html">High-Level Intermediate Representation |
| (<code>HIR</code>)</a>, a more compiler-friendly representation of the <code>AST</code>. This process |
| is called “lowering” and involves a lot of desugaring (the expansion and |
| formalizing of shortened or abbreviated syntax constructs) of things like loops |
| and <code>async fn</code>.</p> |
| <p>We then use the <code>HIR</code> to do <a href="type-inference.html"><em>type inference</em></a> (the process of automatic |
| detection of the type of an expression), <a href="traits/resolution.html"><em>trait solving</em></a> (the process of |
| pairing up an impl with each reference to a <code>trait</code>), and <a href="type-checking.html"><em>type checking</em></a>. Type |
| checking is the process of converting the types found in the <code>HIR</code> (<a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/struct.Ty.html"><code>hir::Ty</code></a>), |
| which represent what the user wrote, into the internal representation used by |
| the compiler (<a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html"><code>Ty<'tcx></code></a>). It’s called type checking because the information |
| is used to verify the type safety, correctness and coherence of the types used |
| in the program.</p> |
| <h3 id="mir-lowering"><a class="header" href="#mir-lowering"><code>MIR</code> lowering</a></h3> |
| <p>The <code>HIR</code> is further lowered to <code>MIR</code> |
| (used for <a href="borrow_check.html">borrow checking</a>) by constructing the <code>THIR</code> (an even more desugared <code>HIR</code> used for |
| pattern and exhaustiveness checking) to convert into <code>MIR</code>.</p> |
| <p>We do <a href="mir/optimizations.html">many optimizations on the MIR</a> because it is generic and that |
| improves later code generation and compilation speed. It is easier to do some |
| optimizations at <code>MIR</code> level than at <code>LLVM-IR</code> level. For example LLVM doesn’t seem |
| to be able to optimize the pattern the <a href="https://github.com/rust-lang/rust/pull/66282"><code>simplify_try</code></a> <code>MIR</code>-opt looks for.</p> |
| <p>Rust code is also <a href="https://en.wikipedia.org/wiki/Monomorphization"><em>monomorphized</em></a> during code generation, which means making |
| copies of all the generic code with the type parameters replaced by concrete |
| types. To do this, we need to collect a list of what concrete types to generate |
| code for. This is called <em>monomorphization collection</em> and it happens at the |
| <code>MIR</code> level.</p> |
| <h3 id="code-generation"><a class="header" href="#code-generation">Code generation</a></h3> |
| <p>We then begin what is simply called <em>code generation</em> or <em>codegen</em>. The <a href="backend/codegen.html">code |
| generation stage</a> is when higher-level representations of source are |
| turned into an executable binary. Since <code>rustc</code> uses LLVM for code generation, |
| the first step is to convert the <code>MIR</code> to <code>LLVM-IR</code>. This is where the <code>MIR</code> is |
| actually monomorphized. The <code>LLVM-IR</code> is passed to LLVM, which does a lot more |
| optimizations on it, emitting machine code which is basically assembly code |
| with additional low-level types and annotations added (e.g. an ELF object or |
| <code>WASM</code>). The different libraries/binaries are then linked together to produce |
| the final binary.</p> |
| <h2 id="how-it-does-it"><a class="header" href="#how-it-does-it">How it does it</a></h2> |
| <p>Now that we have a high-level view of what the compiler does to your code, |
| let’s take a high-level view of <em>how</em> it does all that stuff. There are a lot |
| of constraints and conflicting goals that the compiler needs to |
| satisfy/optimize for. For example,</p> |
| <ul> |
| <li>Compilation speed: how fast is it to compile a program? More/better |
| compile-time analyses often means compilation is slower. |
| <ul> |
| <li>Also, we want to support incremental compilation, so we need to take that |
| into account. How can we keep track of what work needs to be redone and |
| what can be reused if the user modifies their program? |
| <ul> |
| <li>Also we can’t store too much stuff in the incremental cache because |
| it would take a long time to load from disk and it could take a lot |
| of space on the user’s system…</li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| <li>Compiler memory usage: while compiling a program, we don’t want to use more |
| memory than we need.</li> |
| <li>Program speed: how fast is your compiled program? More/better compile-time |
| analyses often means the compiler can do better optimizations.</li> |
| <li>Program size: how large is the compiled binary? Similar to the previous |
| point.</li> |
| <li>Compiler compilation speed: how long does it take to compile the compiler? |
| This impacts contributors and compiler maintenance.</li> |
| <li>Implementation complexity: building a compiler is one of the hardest |
| things a person/group can do, and Rust is not a very simple language, so how |
| do we make the compiler’s code base manageable?</li> |
| <li>Compiler correctness: the binaries produced by the compiler should do what |
| the input programs says they do, and should continue to do so despite the |
| tremendous amount of change constantly going on.</li> |
| <li>Integration: a number of other tools need to use the compiler in |
| various ways (e.g. <code>cargo</code>, <code>clippy</code>, <code>MIRI</code>) that must be supported.</li> |
| <li>Compiler stability: the compiler should not crash or fail ungracefully on the |
| stable channel.</li> |
| <li>Rust stability: the compiler must respect Rust’s stability guarantees by not |
| breaking programs that previously compiled despite the many changes that are |
| always going on to its implementation.</li> |
| <li>Limitations of other tools: <code>rustc</code> uses LLVM in its backend, and LLVM has some |
| strengths we leverage and some aspects we need to work around.</li> |
| </ul> |
| <p>So, as you continue your journey through the rest of the guide, keep these |
| things in mind. They will often inform decisions that we make.</p> |
| <h3 id="intermediate-representations"><a class="header" href="#intermediate-representations">Intermediate representations</a></h3> |
| <p>As with most compilers, <code>rustc</code> uses some intermediate representations (IRs) to |
| facilitate computations. In general, working directly with the source code is |
| extremely inconvenient and error-prone. Source code is designed to be human-friendly while at |
| the same time being unambiguous, but it’s less convenient for doing something |
| like, say, type checking.</p> |
| <p>Instead most compilers, including <code>rustc</code>, build some sort of IR out of the |
| source code which is easier to analyze. <code>rustc</code> has a few IRs, each optimized |
| for different purposes:</p> |
| <ul> |
| <li>Token stream: the lexer produces a stream of tokens directly from the source |
| code. This stream of tokens is easier for the parser to deal with than raw |
| text.</li> |
| <li>Abstract Syntax Tree (<code>AST</code>): the abstract syntax tree is built from the stream |
| of tokens produced by the lexer. It represents |
| pretty much exactly what the user wrote. It helps to do some syntactic sanity |
| checking (e.g. checking that a type is expected where the user wrote one).</li> |
| <li>High-level IR (HIR): This is a sort of desugared <code>AST</code>. It’s still close |
| to what the user wrote syntactically, but it includes some implicit things |
| such as some elided lifetimes, etc. This IR is amenable to type checking.</li> |
| <li>Typed <code>HIR</code> (THIR) <em>formerly High-level Abstract IR (HAIR)</em>: This is an |
| intermediate between <code>HIR</code> and MIR. It is like the <code>HIR</code> but it is fully typed |
| and a bit more desugared (e.g. method calls and implicit dereferences are |
| made fully explicit). As a result, it is easier to lower to <code>MIR</code> from <code>THIR</code> than |
| from HIR.</li> |
| <li>Middle-level IR (<code>MIR</code>): This IR is basically a Control-Flow Graph (CFG). A CFG |
| is a type of diagram that shows the basic blocks of a program and how control |
| flow can go between them. Likewise, <code>MIR</code> also has a bunch of basic blocks with |
| simple typed statements inside them (e.g. assignment, simple computations, |
| etc) and control flow edges to other basic blocks (e.g., calls, dropping |
| values). <code>MIR</code> is used for borrow checking and other |
| important dataflow-based checks, such as checking for uninitialized values. |
| It is also used for a series of optimizations and for constant evaluation (via |
| <code>MIRI</code>). Because <code>MIR</code> is still generic, we can do a lot of analyses here more |
| efficiently than after monomorphization.</li> |
| <li><code>LLVM-IR</code>: This is the standard form of all input to the LLVM compiler. <code>LLVM-IR</code> |
| is a sort of typed assembly language with lots of annotations. It’s |
| a standard format that is used by all compilers that use LLVM (e.g. the clang |
| C compiler also outputs <code>LLVM-IR</code>). <code>LLVM-IR</code> is designed to be easy for other |
| compilers to emit and also rich enough for LLVM to run a bunch of |
| optimizations on it.</li> |
| </ul> |
| <p>One other thing to note is that many values in the compiler are <em>interned</em>. |
| This is a performance and memory optimization in which we allocate the values in |
| a special allocator called an |
| <em><a href="https://en.wikipedia.org/wiki/Region-based_memory_management">arena</a></em>. Then, we pass |
| around references to the values allocated in the arena. This allows us to make |
| sure that identical values (e.g. types in your program) are only allocated once |
| and can be compared cheaply by comparing pointers. Many of the intermediate |
| representations are interned.</p> |
| <h3 id="queries"><a class="header" href="#queries">Queries</a></h3> |
| <p>The first big implementation choice is Rust’s use of the <em>query</em> system in its |
| compiler. The Rust compiler <em>is not</em> organized as a series of passes over the |
| code which execute sequentially. The Rust compiler does this to make |
| incremental compilation possible – that is, if the user makes a change to |
| their program and recompiles, we want to do as little redundant work as |
| possible to output the new binary.</p> |
| <p>In <code>rustc</code>, all the major steps above are organized as a bunch of queries that |
| call each other. For example, there is a query to ask for the type of something |
| and another to ask for the optimized <code>MIR</code> of a function. These queries can call |
| each other and are all tracked through the query system. The results of the |
| queries are cached on disk so that the compiler can tell which queries’ results |
| changed from the last compilation and only redo those. This is how incremental |
| compilation works.</p> |
| <p>In principle, for the query-fied steps, we do each of the above for each item |
| individually. For example, we will take the <code>HIR</code> for a function and use queries |
| to ask for the <code>LLVM-IR</code> for that HIR. This drives the generation of optimized |
| <code>MIR</code>, which drives the borrow checker, which drives the generation of <code>MIR</code>, and |
| so on.</p> |
| <p>… except that this is very over-simplified. In fact, some queries are not |
| cached on disk, and some parts of the compiler have to run for all code anyway |
| for correctness even if the code is dead code (e.g. the borrow checker). For |
| example, <a href="https://github.com/rust-lang/rust/blob/e69c7306e2be08939d95f14229e3f96566fb206c/compiler/rustc_interface/src/passes.rs#L791">currently the <code>mir_borrowck</code> query is first executed on all functions |
| of a crate.</a> Then the codegen backend invokes the |
| <code>collect_and_partition_mono_items</code> query, which first recursively requests the |
| <code>optimized_mir</code> for all reachable functions, which in turn runs <code>mir_borrowck</code> |
| for that function and then creates codegen units. This kind of split will need |
| to remain to ensure that unreachable functions still have their errors emitted.</p> |
| <p>Moreover, the compiler wasn’t originally built to use a query system; the query |
| system has been retrofitted into the compiler, so parts of it are not query-fied |
| yet. Also, LLVM isn’t our code, so that isn’t querified either. The plan is to |
| eventually query-fy all of the steps listed in the previous section, |
| but as of <!-- date-check --> November 2022, only the steps between <code>HIR</code> and |
| <code>LLVM-IR</code> are query-fied. That is, lexing, parsing, name resolution, and macro |
| expansion are done all at once for the whole program.</p> |
| <p>One other thing to mention here is the all-important “typing context”, |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html"><code>TyCtxt</code></a>, which is a giant struct that is at the center of all things. |
| (Note that the name is mostly historic. This is <em>not</em> a “typing context” in the |
| sense of <code>Γ</code> or <code>Δ</code> from type theory. The name is retained because that’s what |
| the name of the struct is in the source code.) All |
| queries are defined as methods on the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html"><code>TyCtxt</code></a> type, and the in-memory query |
| cache is stored there too. In the code, there is usually a variable called |
| <code>tcx</code> which is a handle on the typing context. You will also see lifetimes with |
| the name <code>'tcx</code>, which means that something is tied to the lifetime of the |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html"><code>TyCtxt</code></a> (usually it is stored or interned there).</p> |
| <p>For more information about queries in the compiler, see <a href="./query.html">the queries chapter</a>.</p> |
| <h3 id="tyty"><a class="header" href="#tyty"><code>ty::Ty</code></a></h3> |
| <p>Types are really important in Rust, and they form the core of a lot of compiler |
| analyses. The main type (in the compiler) that represents types (in the user’s |
| program) is <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html"><code>rustc_middle::ty::Ty</code></a>. This is so important that we have a whole chapter |
| on <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html"><code>ty::Ty</code></a>, but for now, we just want to mention that it exists and is the way |
| <code>rustc</code> represents types!</p> |
| <p>Also note that the <a href="https://doc.rust-lang.org/beta/nightly-rustc/rustc_middle/ty/index.html"><code>rustc_middle::ty</code></a> module defines the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html"><code>TyCtxt</code></a> struct we mentioned before.</p> |
| <h3 id="parallelism"><a class="header" href="#parallelism">Parallelism</a></h3> |
| <p>Compiler performance is a problem that we would like to improve on |
| (and are always working on). One aspect of that is parallelizing |
| <code>rustc</code> itself.</p> |
| <p>Currently, there is only one part of rustc that is parallel by default: |
| <a href="./parallel-rustc.html#Codegen">code generation</a>.</p> |
| <p>However, the rest of the compiler is still not yet parallel. There have been |
| lots of efforts spent on this, but it is generally a hard problem. The current |
| approach is to turn <a href="https://doc.rust-lang.org/std/cell/struct.RefCell.html"><code>RefCell</code></a>s into <a href="https://doc.rust-lang.org/std/sync/struct.Mutex.html"><code>Mutex</code></a>s – that is, we |
| switch to thread-safe internal mutability. However, there are ongoing |
| challenges with lock contention, maintaining query-system invariants under |
| concurrency, and the complexity of the code base. One can try out the current |
| work by enabling parallel compilation in <code>bootstrap.toml</code>. It’s still early days, |
| but there are already some promising performance improvements.</p> |
| <h3 id="bootstrapping"><a class="header" href="#bootstrapping">Bootstrapping</a></h3> |
| <p><code>rustc</code> itself is written in Rust. So how do we compile the compiler? We use an |
| older compiler to compile the newer compiler. This is called <a href="https://en.wikipedia.org/wiki/Bootstrapping_(compilers)"><em>bootstrapping</em></a>.</p> |
| <p>Bootstrapping has a lot of interesting implications. For example, it means |
| that one of the major users of Rust is the Rust compiler, so we are |
| constantly testing our own software (“eating our own dogfood”).</p> |
| <p>For more details on bootstrapping, see |
| <a href="building/bootstrapping/intro.html">the bootstrapping section of the guide</a>.</p> |
| <!-- |
| # Unresolved Questions |
| |
| - Does LLVM ever do optimizations in debug builds? |
| - How do I explore phases of the compile process in my own sources (lexer, |
| parser, HIR, etc)? - e.g., `cargo rustc -- -Z unpretty=hir-tree` allows you to |
| view `HIR` representation |
| - What is the main source entry point for `X`? |
| - Where do phases diverge for cross-compilation to machine code across |
| different platforms? |
| --> |
| <h1 id="references"><a class="header" href="#references">References</a></h1> |
| <ul> |
| <li>Command line parsing |
| <ul> |
| <li>Guide: <a href="rustc-driver/intro.html">The Rustc Driver and Interface</a></li> |
| <li>Driver definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/"><code>rustc_driver</code></a></li> |
| <li>Main entry point: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_session/config/fn.build_session_options.html"><code>rustc_session::config::build_session_options</code></a></li> |
| </ul> |
| </li> |
| <li>Lexical Analysis: Lex the user program to a stream of tokens |
| <ul> |
| <li>Guide: <a href="the-parser.html">Lexing and Parsing</a></li> |
| <li>Lexer definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lexer/index.html"><code>rustc_lexer</code></a></li> |
| <li>Main entry point: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lexer/cursor/struct.Cursor.html#method.advance_token"><code>rustc_lexer::cursor::Cursor::advance_token</code></a></li> |
| </ul> |
| </li> |
| <li>Parsing: Parse the stream of tokens to an Abstract Syntax Tree (AST) |
| <ul> |
| <li>Guide: <a href="the-parser.html">Lexing and Parsing</a></li> |
| <li>Guide: <a href="macro-expansion.html">Macro Expansion</a></li> |
| <li>Guide: <a href="name-resolution.html">Name Resolution</a></li> |
| <li>Parser definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html"><code>rustc_parse</code></a></li> |
| <li>Main entry points: |
| <ul> |
| <li><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/passes/fn.parse.html">Entry point for first file in crate</a></li> |
| <li><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_expand/module/fn.parse_external_mod.html">Entry point for outline module parsing</a></li> |
| <li><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html#method.parse_nonterminal">Entry point for macro fragments</a></li> |
| </ul> |
| </li> |
| <li><code>AST</code> definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/index.html"><code>rustc_ast</code></a></li> |
| <li>Feature gating: <strong>TODO</strong></li> |
| <li>Early linting: <strong>TODO</strong></li> |
| </ul> |
| </li> |
| <li>The High Level Intermediate Representation (HIR) |
| <ul> |
| <li>Guide: <a href="hir.html">The HIR</a></li> |
| <li>Guide: <a href="hir.html#identifiers-in-the-hir">Identifiers in the HIR</a></li> |
| <li>Guide: <a href="hir.html#the-hir-map">The <code>HIR</code> Map</a></li> |
| <li>Guide: <a href="./hir/lowering.html">Lowering <code>AST</code> to <code>HIR</code></a></li> |
| <li>How to view <code>HIR</code> representation for your code <code>cargo rustc -- -Z unpretty=hir-tree</code></li> |
| <li>Rustc <code>HIR</code> definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/index.html"><code>rustc_hir</code></a></li> |
| <li>Main entry point: <strong>TODO</strong></li> |
| <li>Late linting: <strong>TODO</strong></li> |
| </ul> |
| </li> |
| <li>Type Inference |
| <ul> |
| <li>Guide: <a href="type-inference.html">Type Inference</a></li> |
| <li>Guide: <a href="ty.html">The ty Module: Representing Types</a> (semantics)</li> |
| <li>Main entry point (type inference): <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_infer/infer/struct.InferCtxtBuilder.html#method.enter"><code>InferCtxtBuilder::enter</code></a></li> |
| <li>Main entry point (type checking bodies): <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html#method.typeck">the <code>typeck</code> query</a> |
| <ul> |
| <li>These two functions can’t be decoupled.</li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| <li>The Mid Level Intermediate Representation (MIR) |
| <ul> |
| <li>Guide: <a href="mir/index.html">The <code>MIR</code> (Mid level IR)</a></li> |
| <li>Definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/index.html"><code>rustc_middle/src/mir</code></a></li> |
| <li>Definition of sources that manipulates the MIR: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_build/index.html"><code>rustc_mir_build</code></a>, <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_dataflow/index.html"><code>rustc_mir_dataflow</code></a>, <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/index.html"><code>rustc_mir_transform</code></a></li> |
| </ul> |
| </li> |
| <li>The Borrow Checker |
| <ul> |
| <li>Guide: <a href="borrow_check.html">MIR Borrow Check</a></li> |
| <li>Definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_borrowck/index.html"><code>rustc_borrowck</code></a></li> |
| <li>Main entry point: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_borrowck/fn.mir_borrowck.html"><code>mir_borrowck</code> query</a></li> |
| </ul> |
| </li> |
| <li><code>MIR</code> Optimizations |
| <ul> |
| <li>Guide: <a href="mir/optimizations.html">MIR Optimizations</a></li> |
| <li>Definition: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/index.html"><code>rustc_mir_transform</code></a></li> |
| <li>Main entry point: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/fn.optimized_mir.html"><code>optimized_mir</code> query</a></li> |
| </ul> |
| </li> |
| <li>Code Generation |
| <ul> |
| <li>Guide: <a href="backend/codegen.html">Code Generation</a></li> |
| <li>Generating Machine Code from <code>LLVM-IR</code> with LLVM - <strong>TODO: reference?</strong></li> |
| <li>Main entry point: <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/base/fn.codegen_crate.html"><code>rustc_codegen_ssa::base::codegen_crate</code></a> |
| <ul> |
| <li>This monomorphizes and produces <code>LLVM-IR</code> for one codegen unit. It then |
| starts a background thread to run LLVM, which must be joined later.</li> |
| <li>Monomorphization happens lazily via <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/mir/struct.FunctionCx.html#method.monomorphize"><code>FunctionCx::monomorphize</code></a> and <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/base/fn.codegen_instance.html"><code>rustc_codegen_ssa::base::codegen_instance </code></a></li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| </ul> |
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