124 lines
5.6 KiB
Go
124 lines
5.6 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package ssa defines a representation of the elements of Go programs
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// (packages, types, functions, variables and constants) using a
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// static single-assignment (SSA) form intermediate representation
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// (IR) for the bodies of functions.
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//
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// THIS INTERFACE IS EXPERIMENTAL AND IS LIKELY TO CHANGE.
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//
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// For an introduction to SSA form, see
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// http://en.wikipedia.org/wiki/Static_single_assignment_form.
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// This page provides a broader reading list:
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// http://www.dcs.gla.ac.uk/~jsinger/ssa.html.
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//
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// The level of abstraction of the SSA form is intentionally close to
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// the source language to facilitate construction of source analysis
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// tools. It is not intended for machine code generation.
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//
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// All looping, branching and switching constructs are replaced with
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// unstructured control flow. Higher-level control flow constructs
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// such as multi-way branch can be reconstructed as needed; see
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// ssautil.Switches() for an example.
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//
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// To construct an SSA-form program, call ssautil.CreateProgram on a
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// loader.Program, a set of type-checked packages created from
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// parsed Go source files. The resulting ssa.Program contains all the
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// packages and their members, but SSA code is not created for
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// function bodies until a subsequent call to (*Package).Build.
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//
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// The builder initially builds a naive SSA form in which all local
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// variables are addresses of stack locations with explicit loads and
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// stores. Registerisation of eligible locals and φ-node insertion
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// using dominance and dataflow are then performed as a second pass
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// called "lifting" to improve the accuracy and performance of
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// subsequent analyses; this pass can be skipped by setting the
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// NaiveForm builder flag.
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//
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// The primary interfaces of this package are:
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//
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// - Member: a named member of a Go package.
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// - Value: an expression that yields a value.
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// - Instruction: a statement that consumes values and performs computation.
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// - Node: a Value or Instruction (emphasizing its membership in the SSA value graph)
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//
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// A computation that yields a result implements both the Value and
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// Instruction interfaces. The following table shows for each
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// concrete type which of these interfaces it implements.
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//
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// Value? Instruction? Member?
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// *Alloc ✔ ✔
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// *BinOp ✔ ✔
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// *Builtin ✔
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// *Call ✔ ✔
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// *ChangeInterface ✔ ✔
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// *ChangeType ✔ ✔
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// *Const ✔
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// *Convert ✔ ✔
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// *DebugRef ✔
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// *Defer ✔
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// *Extract ✔ ✔
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// *Field ✔ ✔
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// *FieldAddr ✔ ✔
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// *FreeVar ✔
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// *Function ✔ ✔ (func)
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// *Global ✔ ✔ (var)
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// *Go ✔
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// *If ✔
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// *Index ✔ ✔
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// *IndexAddr ✔ ✔
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// *Jump ✔
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// *Lookup ✔ ✔
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// *MakeChan ✔ ✔
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// *MakeClosure ✔ ✔
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// *MakeInterface ✔ ✔
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// *MakeMap ✔ ✔
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// *MakeSlice ✔ ✔
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// *MapUpdate ✔
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// *NamedConst ✔ (const)
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// *Next ✔ ✔
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// *Panic ✔
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// *Parameter ✔
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// *Phi ✔ ✔
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// *Range ✔ ✔
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// *Return ✔
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// *RunDefers ✔
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// *Select ✔ ✔
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// *Send ✔
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// *Slice ✔ ✔
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// *Store ✔
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// *Type ✔ (type)
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// *TypeAssert ✔ ✔
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// *UnOp ✔ ✔
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//
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// Other key types in this package include: Program, Package, Function
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// and BasicBlock.
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//
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// The program representation constructed by this package is fully
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// resolved internally, i.e. it does not rely on the names of Values,
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// Packages, Functions, Types or BasicBlocks for the correct
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// interpretation of the program. Only the identities of objects and
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// the topology of the SSA and type graphs are semantically
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// significant. (There is one exception: Ids, used to identify field
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// and method names, contain strings.) Avoidance of name-based
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// operations simplifies the implementation of subsequent passes and
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// can make them very efficient. Many objects are nonetheless named
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// to aid in debugging, but it is not essential that the names be
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// either accurate or unambiguous. The public API exposes a number of
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// name-based maps for client convenience.
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//
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// The ssa/ssautil package provides various utilities that depend only
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// on the public API of this package.
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//
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// TODO(adonovan): Consider the exceptional control-flow implications
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// of defer and recover().
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//
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// TODO(adonovan): write a how-to document for all the various cases
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// of trying to determine corresponding elements across the four
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// domains of source locations, ast.Nodes, types.Objects,
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// ssa.Values/Instructions.
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//
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package ssa // import "golang.org/x/tools/go/ssa"
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