1 // Copyright 2013 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package ir defines a representation of the elements of Go programs
6 // (packages, types, functions, variables and constants) using a
7 // static single-information (SSI) form intermediate representation
8 // (IR) for the bodies of functions.
10 // THIS INTERFACE IS EXPERIMENTAL AND IS LIKELY TO CHANGE.
12 // For an introduction to SSA form, upon which SSI builds, see
13 // http://en.wikipedia.org/wiki/Static_single_assignment_form.
14 // This page provides a broader reading list:
15 // http://www.dcs.gla.ac.uk/~jsinger/ssa.html.
17 // For an introduction to SSI form, see The static single information
18 // form by C. Scott Ananian.
20 // The level of abstraction of the IR form is intentionally close to
21 // the source language to facilitate construction of source analysis
22 // tools. It is not intended for machine code generation.
24 // The simplest way to create the IR of a package is
25 // to load typed syntax trees using golang.org/x/tools/go/packages, then
26 // invoke the irutil.Packages helper function. See ExampleLoadPackages
27 // and ExampleWholeProgram for examples.
28 // The resulting ir.Program contains all the packages and their
29 // members, but IR code is not created for function bodies until a
30 // subsequent call to (*Package).Build or (*Program).Build.
32 // The builder initially builds a naive IR form in which all local
33 // variables are addresses of stack locations with explicit loads and
34 // stores. Registerisation of eligible locals and φ-node insertion
35 // using dominance and dataflow are then performed as a second pass
36 // called "lifting" to improve the accuracy and performance of
37 // subsequent analyses; this pass can be skipped by setting the
38 // NaiveForm builder flag.
40 // The primary interfaces of this package are:
42 // - Member: a named member of a Go package.
43 // - Value: an expression that yields a value.
44 // - Instruction: a statement that consumes values and performs computation.
45 // - Node: a Value or Instruction (emphasizing its membership in the IR value graph)
47 // A computation that yields a result implements both the Value and
48 // Instruction interfaces. The following table shows for each
49 // concrete type which of these interfaces it implements.
51 // Value? Instruction? Member?
57 // *ChangeInterface ✔ ✔
67 // *Function ✔ ✔ (func)
82 // *NamedConst ✔ (const)
102 // Other key types in this package include: Program, Package, Function
105 // The program representation constructed by this package is fully
106 // resolved internally, i.e. it does not rely on the names of Values,
107 // Packages, Functions, Types or BasicBlocks for the correct
108 // interpretation of the program. Only the identities of objects and
109 // the topology of the IR and type graphs are semantically
110 // significant. (There is one exception: Ids, used to identify field
111 // and method names, contain strings.) Avoidance of name-based
112 // operations simplifies the implementation of subsequent passes and
113 // can make them very efficient. Many objects are nonetheless named
114 // to aid in debugging, but it is not essential that the names be
115 // either accurate or unambiguous. The public API exposes a number of
116 // name-based maps for client convenience.
118 // The ir/irutil package provides various utilities that depend only
119 // on the public API of this package.
121 // TODO(adonovan): Consider the exceptional control-flow implications
122 // of defer and recover().
124 // TODO(adonovan): write a how-to document for all the various cases
125 // of trying to determine corresponding elements across the four
126 // domains of source locations, ast.Nodes, types.Objects,
127 // ir.Values/Instructions.
129 package ir // import "honnef.co/go/tools/ir"
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