94 lines
3.7 KiB
Plaintext
94 lines
3.7 KiB
Plaintext
An informal guide to reading and working on the rustc compiler.
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==================================================================
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If you wish to expand on this document, or have a more experienced
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Rust contributor add anything else to it, please get in touch:
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https://github.com/mozilla/rust/wiki/Note-development-policy
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("Communication" subheading)
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or file a bug:
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https://github.com/mozilla/rust/issues
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Your concerns are probably the same as someone else's.
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High-level concepts
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===================
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Rustc consists of the following subdirectories:
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front/ - front-end: attributes, conditional compilation
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middle/ - middle-end: name resolution, typechecking, LLVM code
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generation
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back/ - back-end: linking and ABI
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metadata/ - encoder and decoder for data required by
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separate compilation
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driver/ - command-line processing, main() entrypoint
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util/ - ubiquitous types and helper functions
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lib/ - bindings to LLVM
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The files concerned purely with syntax -- that is, the AST, parser,
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pretty-printer, lexer, macro expander, and utilities for traversing
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ASTs -- are in a separate crate called "syntax", whose files are in
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./../libsyntax, where . is the current directory (that is, the parent
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directory of front/, middle/, back/, and so on).
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The entry-point for the compiler is main() in lib.rs, and
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this file sequences the various parts together.
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The 3 central data structures:
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------------------------------
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#1: ./../libsyntax/ast.rs defines the AST. The AST is treated as immutable
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after parsing, but it depends on mutable context data structures
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(mainly hash maps) to give it meaning.
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- Many -- though not all -- nodes within this data structure are
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wrapped in the type `spanned<T>`, meaning that the front-end has
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marked the input coordinates of that node. The member .node is
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the data itself, the member .span is the input location (file,
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line, column; both low and high).
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- Many other nodes within this data structure carry a
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def_id. These nodes represent the 'target' of some name
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reference elsewhere in the tree. When the AST is resolved, by
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middle/resolve.rs, all names wind up acquiring a def that they
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point to. So anything that can be pointed-to by a name winds
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up with a def_id.
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#2: middle/ty.rs defines the datatype sty. This is the type that
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represents types after they have been resolved and normalized by
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the middle-end. The typeck phase converts every ast type to a
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ty::sty, and the latter is used to drive later phases of
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compilation. Most variants in the ast::ty tag have a
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corresponding variant in the ty::sty tag.
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#3: lib/llvm.rs defines the exported types ValueRef, TypeRef,
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BasicBlockRef, and several others. Each of these is an opaque
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pointer to an LLVM type, manipulated through the lib::llvm
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interface.
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Control and information flow within the compiler:
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-------------------------------------------------
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- main() in lib.rs assumes control on startup. Options are
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parsed, platform is detected, etc.
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- ./../libsyntax/parse/parser.rs parses the input files and produces an AST
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that represents the input crate.
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- Multiple middle-end passes (middle/resolve.rs, middle/typeck.rs)
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analyze the semantics of the resulting AST. Each pass generates new
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information about the AST and stores it in various environment data
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structures. The driver passes environments to each compiler pass
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that needs to refer to them.
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- Finally middle/trans.rs translates the Rust AST to LLVM bitcode in a
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type-directed way. When it's finished synthesizing LLVM values,
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rustc asks LLVM to write them out in some form (.bc, .o) and
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possibly run the system linker.
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