ssa

package
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 Go to latest Published: Jan 9, 2018 License: MIT, MIT Imports: 19 Imported by: 0

Documentation

Overview

Package ssa defines a representation of the elements of Go programs (packages, types, functions, variables and constants) using a static single-assignment (SSA) form intermediate representation (IR) for the bodies of functions.

THIS INTERFACE IS EXPERIMENTAL AND IS LIKELY TO CHANGE.

For an introduction to SSA form, see http://en.wikipedia.org/wiki/Static_single_assignment_form. This page provides a broader reading list: http://www.dcs.gla.ac.uk/~jsinger/ssa.html.

The level of abstraction of the SSA form is intentionally close to the source language to facilitate construction of source analysis tools. It is not intended for machine code generation.

All looping, branching and switching constructs are replaced with unstructured control flow. Higher-level control flow constructs such as multi-way branch can be reconstructed as needed; see ssautil.Switches() for an example.

To construct an SSA-form program, call ssautil.CreateProgram on a loader.Program, a set of type-checked packages created from parsed Go source files. The resulting ssa.Program contains all the packages and their members, but SSA code is not created for function bodies until a subsequent call to (*Package).Build.

The builder initially builds a naive SSA form in which all local variables are addresses of stack locations with explicit loads and stores. Registerisation of eligible locals and φ-node insertion using dominance and dataflow are then performed as a second pass called "lifting" to improve the accuracy and performance of subsequent analyses; this pass can be skipped by setting the NaiveForm builder flag.

The primary interfaces of this package are:

  • Member: a named member of a Go package.
  • Value: an expression that yields a value.
  • Instruction: a statement that consumes values and performs computation.
  • Node: a Value or Instruction (emphasizing its membership in the SSA value graph)

A computation that yields a result implements both the Value and Instruction interfaces. The following table shows for each concrete type which of these interfaces it implements. 

                   Value?          Instruction?    Member?
*Alloc             ✔               ✔
*BinOp             ✔               ✔
*Builtin           ✔
*Call              ✔               ✔
*ChangeInterface   ✔               ✔
*ChangeType        ✔               ✔
*Const             ✔
*Convert           ✔               ✔
*DebugRef                          ✔
*Defer                             ✔
*Extract           ✔               ✔
*Field             ✔               ✔
*FieldAddr         ✔               ✔
*FreeVar           ✔
*Function          ✔                               ✔ (func)
*Global            ✔                               ✔ (var)
*Go                                ✔
*If                                ✔
*Index             ✔               ✔
*IndexAddr         ✔               ✔
*Jump                              ✔
*Lookup            ✔               ✔
*MakeChan          ✔               ✔
*MakeClosure       ✔               ✔
*MakeInterface     ✔               ✔
*MakeMap           ✔               ✔
*MakeSlice         ✔               ✔
*MapUpdate                         ✔
*NamedConst                                        ✔ (const)
*Next              ✔               ✔
*Panic                             ✔
*Parameter         ✔
*Phi               ✔               ✔
*Range             ✔               ✔
*Return                            ✔
*RunDefers                         ✔
*Select            ✔               ✔
*Send                              ✔
*Slice             ✔               ✔
*Store                             ✔
*Type                                              ✔ (type)
*TypeAssert        ✔               ✔
*UnOp              ✔               ✔

Other key types in this package include: Program, Package, Function and BasicBlock.

The program representation constructed by this package is fully resolved internally, i.e. it does not rely on the names of Values, Packages, Functions, Types or BasicBlocks for the correct interpretation of the program. Only the identities of objects and the topology of the SSA and type graphs are semantically significant. (There is one exception: Ids, used to identify field and method names, contain strings.) Avoidance of name-based operations simplifies the implementation of subsequent passes and can make them very efficient. Many objects are nonetheless named to aid in debugging, but it is not essential that the names be either accurate or unambiguous. The public API exposes a number of name-based maps for client convenience.

The ssa/ssautil package provides various utilities that depend only on the public API of this package.

TODO(adonovan): Consider the exceptional control-flow implications of defer and recover().

TODO(adonovan): write a how-to document for all the various cases of trying to determine corresponding elements across the four domains of source locations, ast.Nodes, types.Objects, ssa.Values/Instructions.

Index

Constants

View Source 
const BuilderModeDoc = `` /* 504-byte string literal not displayed */

Variables

This section is empty.

Functions

func DefaultType 

func DefaultType(typ types.Type) types.Type

DefaultType returns the default "typed" type for an "untyped" type; it returns the incoming type for all other types. The default type for untyped nil is untyped nil.

Exported to ssa/interp.

TODO(gri): this is a copy of go/types.defaultType; export that function.

func DeleteUnreachableBlocks 

func DeleteUnreachableBlocks(f *Function)

func FindTests 

func FindTests(pkg *Package) (tests, benchmarks, examples []*Function, main *Function)

FindTests returns the Test, Benchmark, and Example functions (as defined by "go test") defined in the specified package, and its TestMain function, if any.

func HasEnclosingFunction 

func HasEnclosingFunction(pkg *Package, path []ast.Node) bool

HasEnclosingFunction returns true if the AST node denoted by path is contained within the declaration of some function or package-level variable.

Unlike EnclosingFunction, the behaviour of this function does not depend on whether SSA code for pkg has been built, so it can be used to quickly reject check inputs that will cause EnclosingFunction to fail, prior to SSA building.

func OptimizeBlocks 

func OptimizeBlocks(f *Function)

func ReplaceAll 

func ReplaceAll(x, y Value)

func WriteFunction 

func WriteFunction(buf *bytes.Buffer, f *Function)

WriteFunction writes to buf a human-readable "disassembly" of f.

func WritePackage 

func WritePackage(buf *bytes.Buffer, p *Package)

WritePackage writes to buf a human-readable summary of p.

Types

type Alloc 

type Alloc struct {
	Comment string
	Heap    bool
	// contains filtered or unexported fields
}

The Alloc instruction reserves space for a variable of the given type, zero-initializes it, and yields its address.

Alloc values are always addresses, and have pointer types, so the type of the allocated variable is actually Type().Underlying().(*types.Pointer).Elem().

If Heap is false, Alloc allocates space in the function's activation record (frame); we refer to an Alloc(Heap=false) as a "local" alloc. Each local Alloc returns the same address each time it is executed within the same activation; the space is re-initialized to zero.

If Heap is true, Alloc allocates space in the heap; we refer to an Alloc(Heap=true) as a "new" alloc. Each new Alloc returns a different address each time it is executed.

When Alloc is applied to a channel, map or slice type, it returns the address of an uninitialized (nil) reference of that kind; store the result of MakeSlice, MakeMap or MakeChan in that location to instantiate these types.

Pos() returns the ast.CompositeLit.Lbrace for a composite literal, or the ast.CallExpr.Rparen for a call to new() or for a call that allocates a varargs slice.

Example printed form: 

t0 = local int
t1 = new int

func (*Alloc) Name 

func (v *Alloc) Name() string

func (*Alloc) Operands 

func (v *Alloc) Operands(rands []*Value) []*Value

func (*Alloc) Pos 

func (v *Alloc) Pos() token.Pos

func (*Alloc) Referrers 

func (v *Alloc) Referrers() *[]Instruction

func (*Alloc) String 

func (v *Alloc) String() string

func (*Alloc) Type 

func (v *Alloc) Type() types.Type

type BasicBlock 

type BasicBlock struct {
	Index   int    // index of this block within Parent().Blocks
	Comment string // optional label; no semantic significance

	Instrs       []Instruction // instructions in order
	Preds, Succs []*BasicBlock // predecessors and successors
	// contains filtered or unexported fields
}

BasicBlock represents an SSA basic block.

The final element of Instrs is always an explicit transfer of control (If, Jump, Return, or Panic).

A block may contain no Instructions only if it is unreachable, i.e., Preds is nil. Empty blocks are typically pruned.

BasicBlocks and their Preds/Succs relation form a (possibly cyclic) graph independent of the SSA Value graph: the control-flow graph or CFG. It is illegal for multiple edges to exist between the same pair of blocks.

Each BasicBlock is also a node in the dominator tree of the CFG. The tree may be navigated using Idom()/Dominees() and queried using Dominates().

The order of Preds and Succs is significant (to Phi and If instructions, respectively).

func (*BasicBlock) Dominates 

func (b *BasicBlock) Dominates(c *BasicBlock) bool

Dominates reports whether b dominates c.

func (*BasicBlock) Dominees 

func (b *BasicBlock) Dominees() []*BasicBlock

Dominees returns the list of blocks that b immediately dominates: its children in the dominator tree.

func (*BasicBlock) Idom 

func (b *BasicBlock) Idom() *BasicBlock

Idom returns the block that immediately dominates b: its parent in the dominator tree, if any. Neither the entry node (b.Index==0) nor recover node (b==b.Parent().Recover()) have a parent.

func (*BasicBlock) Parent 

func (b *BasicBlock) Parent() *Function

Parent returns the function that contains block b.

func (*BasicBlock) Phis 

func (b *BasicBlock) Phis() []Instruction

func (*BasicBlock) RemovePred 

func (b *BasicBlock) RemovePred(p *BasicBlock)

func (*BasicBlock) String 

func (b *BasicBlock) String() string

String returns a human-readable label of this block. It is not guaranteed unique within the function.

type BinOp 

type BinOp struct {

	// One of:
	// ADD SUB MUL QUO REM          + - * / %
	// AND OR XOR SHL SHR AND_NOT   & | ^ << >> &~
	// EQL LSS GTR NEQ LEQ GEQ      == != < <= < >=
	Op   token.Token
	X, Y Value
	// contains filtered or unexported fields
}

The BinOp instruction yields the result of binary operation X Op Y.

Pos() returns the ast.BinaryExpr.OpPos, if explicit in the source.

Example printed form: 

t1 = t0 + 1:int

func (*BinOp) Name 

func (v *BinOp) Name() string

func (*BinOp) Operands 

func (v *BinOp) Operands(rands []*Value) []*Value

func (*BinOp) Pos 

func (v *BinOp) Pos() token.Pos

func (*BinOp) Referrers 

func (v *BinOp) Referrers() *[]Instruction

func (*BinOp) String 

func (v *BinOp) String() string

func (*BinOp) Type 

func (v *BinOp) Type() types.Type

type BlankStore 

type BlankStore struct {
	Val Value
	// contains filtered or unexported fields
}

The BlankStore instruction is emitted for assignments to the blank identifier.

BlankStore is a pseudo-instruction: it has no dynamic effect.

Pos() returns NoPos.

Example printed form: 

_ = t0

func (*BlankStore) Block 

func (v *BlankStore) Block() *BasicBlock

func (*BlankStore) Operands 

func (s *BlankStore) Operands(rands []*Value) []*Value

func (*BlankStore) Parent 

func (v *BlankStore) Parent() *Function

func (*BlankStore) Pos 

func (s *BlankStore) Pos() token.Pos

func (*BlankStore) Referrers 

func (v *BlankStore) Referrers() *[]Instruction

func (*BlankStore) String 

func (s *BlankStore) String() string

type BuilderMode 

type BuilderMode uint

BuilderMode is a bitmask of options for diagnostics and checking.

*BuilderMode satisfies the flag.Value interface. Example: 

var mode = ssa.BuilderMode(0)
func init() { flag.Var(&mode, "build", ssa.BuilderModeDoc) }

const (
	PrintPackages        BuilderMode = 1 << iota // Print package inventory to stdout
	PrintFunctions                               // Print function SSA code to stdout
	LogSource                                    // Log source locations as SSA builder progresses
	SanityCheckFunctions                         // Perform sanity checking of function bodies
	NaiveForm                                    // Build naïve SSA form: don't replace local loads/stores with registers
	BuildSerially                                // Build packages serially, not in parallel.
	GlobalDebug                                  // Enable debug info for all packages
	BareInits                                    // Build init functions without guards or calls to dependent inits
)

func (BuilderMode) Get 

func (m BuilderMode) Get() interface{}

Get returns m.

func (*BuilderMode) Set 

func (m *BuilderMode) Set(s string) error

Set parses the flag characters in s and updates *m.

func (BuilderMode) String 

func (m BuilderMode) String() string

type Builtin 

type Builtin struct {
	// contains filtered or unexported fields
}

A Builtin represents a specific use of a built-in function, e.g. len.

Builtins are immutable values. Builtins do not have addresses. Builtins can only appear in CallCommon.Func.

Name() indicates the function: one of the built-in functions from the Go spec (excluding "make" and "new") or one of these ssa-defined intrinsics: 

// wrapnilchk returns ptr if non-nil, panics otherwise.
// (For use in indirection wrappers.)
func ssa:wrapnilchk(ptr *T, recvType, methodName string) *T

Object() returns a *types.Builtin for built-ins defined by the spec, nil for others.

Type() returns a *types.Signature representing the effective signature of the built-in for this call.

func (*Builtin) Name 

func (v *Builtin) Name() string

func (*Builtin) Object 

func (v *Builtin) Object() types.Object

func (*Builtin) Operands 

func (v *Builtin) Operands(rands []*Value) []*Value

Non-Instruction Values:

func (*Builtin) Parent 

func (v *Builtin) Parent() *Function

func (*Builtin) Pos 

func (v *Builtin) Pos() token.Pos

func (*Builtin) Referrers 

func (*Builtin) Referrers() *[]Instruction

func (*Builtin) String 

func (v *Builtin) String() string

func (*Builtin) Type 

func (v *Builtin) Type() types.Type

type Call 

type Call struct {
	Call CallCommon
	// contains filtered or unexported fields
}

The Call instruction represents a function or method call.

The Call instruction yields the function result if there is exactly one. Otherwise it returns a tuple, the components of which are accessed via Extract.

See CallCommon for generic function call documentation.

Pos() returns the ast.CallExpr.Lparen, if explicit in the source.

Example printed form: 

t2 = println(t0, t1)
t4 = t3()
t7 = invoke t5.Println(...t6)

func (*Call) Common 

func (s *Call) Common() *CallCommon

func (*Call) Name 

func (v *Call) Name() string

func (*Call) Operands 

func (s *Call) Operands(rands []*Value) []*Value

func (*Call) Pos 

func (v *Call) Pos() token.Pos

func (*Call) Referrers 

func (v *Call) Referrers() *[]Instruction

func (*Call) String 

func (v *Call) String() string

func (*Call) Type 

func (v *Call) Type() types.Type

func (*Call) Value 

func (s *Call) Value() *Call

type CallCommon 

type CallCommon struct {
	Value  Value       // receiver (invoke mode) or func value (call mode)
	Method *types.Func // abstract method (invoke mode)
	Args   []Value     // actual parameters (in static method call, includes receiver)
	// contains filtered or unexported fields
}

CallCommon is contained by Go, Defer and Call to hold the common parts of a function or method call.

Each CallCommon exists in one of two modes, function call and interface method invocation, or "call" and "invoke" for short.

1. "call" mode: when Method is nil (!IsInvoke), a CallCommon represents an ordinary function call of the value in Value, which may be a *Builtin, a *Function or any other value of kind 'func'.

Value may be one of: 

(a) a *Function, indicating a statically dispatched call
    to a package-level function, an anonymous function, or
    a method of a named type.
(b) a *MakeClosure, indicating an immediately applied
    function literal with free variables.
(c) a *Builtin, indicating a statically dispatched call
    to a built-in function.
(d) any other value, indicating a dynamically dispatched
    function call.

StaticCallee returns the identity of the callee in cases (a) and (b), nil otherwise.

Args contains the arguments to the call. If Value is a method, Args[0] contains the receiver parameter.

Example printed form: 

t2 = println(t0, t1)
go t3()
defer t5(...t6)

2. "invoke" mode: when Method is non-nil (IsInvoke), a CallCommon represents a dynamically dispatched call to an interface method. In this mode, Value is the interface value and Method is the interface's abstract method. Note: an abstract method may be shared by multiple interfaces due to embedding; Value.Type() provides the specific interface used for this call.

Value is implicitly supplied to the concrete method implementation as the receiver parameter; in other words, Args[0] holds not the receiver but the first true argument.

Example printed form: 

t1 = invoke t0.String()
go invoke t3.Run(t2)
defer invoke t4.Handle(...t5)

For all calls to variadic functions (Signature().Variadic()), the last element of Args is a slice.

func (*CallCommon) Description 

func (c *CallCommon) Description() string

Description returns a description of the mode of this call suitable for a user interface, e.g., "static method call".

func (*CallCommon) IsInvoke 

func (c *CallCommon) IsInvoke() bool

IsInvoke returns true if this call has "invoke" (not "call") mode.

func (*CallCommon) Operands 

func (c *CallCommon) Operands(rands []*Value) []*Value

func (*CallCommon) Pos 

func (c *CallCommon) Pos() token.Pos

func (*CallCommon) Signature 

func (c *CallCommon) Signature() *types.Signature

Signature returns the signature of the called function.

For an "invoke"-mode call, the signature of the interface method is returned.

In either "call" or "invoke" mode, if the callee is a method, its receiver is represented by sig.Recv, not sig.Params().At(0).

func (*CallCommon) StaticCallee 

func (c *CallCommon) StaticCallee() *Function

StaticCallee returns the callee if this is a trivially static "call"-mode call to a function.

func (*CallCommon) String 

func (c *CallCommon) String() string

type CallInstruction 

type CallInstruction interface {
	Instruction
	Common() *CallCommon // returns the common parts of the call
	Value() *Call        // returns the result value of the call (*Call) or nil (*Go, *Defer)
}

The CallInstruction interface, implemented by *Go, *Defer and *Call, exposes the common parts of function-calling instructions, yet provides a way back to the Value defined by *Call alone.

type ChangeInterface 

type ChangeInterface struct {
	X Value
	// contains filtered or unexported fields
}

ChangeInterface constructs a value of one interface type from a value of another interface type known to be assignable to it. This operation cannot fail.

Pos() returns the ast.CallExpr.Lparen if the instruction arose from an explicit T(e) conversion; the ast.TypeAssertExpr.Lparen if the instruction arose from an explicit e.(T) operation; or token.NoPos otherwise.

Example printed form: 

t1 = change interface interface{} <- I (t0)

func (*ChangeInterface) Name 

func (v *ChangeInterface) Name() string

func (*ChangeInterface) Operands 

func (v *ChangeInterface) Operands(rands []*Value) []*Value

func (*ChangeInterface) Pos 

func (v *ChangeInterface) Pos() token.Pos

func (*ChangeInterface) Referrers 

func (v *ChangeInterface) Referrers() *[]Instruction

func (*ChangeInterface) String 

func (v *ChangeInterface) String() string

func (*ChangeInterface) Type 

func (v *ChangeInterface) Type() types.Type

type ChangeType 

type ChangeType struct {
	X Value
	// contains filtered or unexported fields
}

The ChangeType instruction applies to X a value-preserving type change to Type().

Type changes are permitted:

  • between a named type and its underlying type.
  • between two named types of the same underlying type.
  • between (possibly named) pointers to identical base types.
  • from a bidirectional channel to a read- or write-channel, optionally adding/removing a name.

This operation cannot fail dynamically.

Pos() returns the ast.CallExpr.Lparen, if the instruction arose from an explicit conversion in the source.

Example printed form: 

t1 = changetype *int <- IntPtr (t0)

func (*ChangeType) Name 

func (v *ChangeType) Name() string

func (*ChangeType) Operands 

func (v *ChangeType) Operands(rands []*Value) []*Value

func (*ChangeType) Pos 

func (v *ChangeType) Pos() token.Pos

func (*ChangeType) Referrers 

func (v *ChangeType) Referrers() *[]Instruction

func (*ChangeType) String 

func (v *ChangeType) String() string

func (*ChangeType) Type 

func (v *ChangeType) Type() types.Type

type Const 

type Const struct {
	Value exact.Value
	// contains filtered or unexported fields
}

A Const represents the value of a constant expression.

The underlying type of a constant may be any boolean, numeric, or string type. In addition, a Const may represent the nil value of any reference type---interface, map, channel, pointer, slice, or function---but not "untyped nil".

All source-level constant expressions are represented by a Const of the same type and value.

Value holds the exact value of the constant, independent of its Type(), using the same representation as package go/exact uses for constants, or nil for a typed nil value.

Pos() returns token.NoPos.

Example printed form: 

42:int
"hello":untyped string
3+4i:MyComplex

func NewConst 

func NewConst(val exact.Value, typ types.Type) *Const

NewConst returns a new constant of the specified value and type. val must be valid according to the specification of Const.Value.

func (*Const) Complex128 

func (c *Const) Complex128() complex128

Complex128 returns the complex value of this constant truncated to fit a complex128.

func (*Const) Float64 

func (c *Const) Float64() float64

Float64 returns the numeric value of this constant truncated to fit a float64.

func (*Const) Int64 

func (c *Const) Int64() int64

Int64 returns the numeric value of this constant truncated to fit a signed 64-bit integer.

func (*Const) IsNil 

func (c *Const) IsNil() bool

IsNil returns true if this constant represents a typed or untyped nil value.

func (*Const) Name 

func (c *Const) Name() string

func (*Const) Operands 

func (v *Const) Operands(rands []*Value) []*Value

func (*Const) Parent 

func (c *Const) Parent() *Function

func (*Const) Pos 

func (c *Const) Pos() token.Pos

func (*Const) Referrers 

func (c *Const) Referrers() *[]Instruction

func (*Const) RelString 

func (c *Const) RelString(from *types.Package) string

func (*Const) String 

func (c *Const) String() string

func (*Const) Type 

func (c *Const) Type() types.Type

func (*Const) Uint64 

func (c *Const) Uint64() uint64

Uint64 returns the numeric value of this constant truncated to fit an unsigned 64-bit integer.

type Convert 

type Convert struct {
	X Value
	// contains filtered or unexported fields
}

The Convert instruction yields the conversion of value X to type Type(). One or both of those types is basic (but possibly named).

A conversion may change the value and representation of its operand. Conversions are permitted:

  • between real numeric types.
  • between complex numeric types.
  • between string and []byte or []rune.
  • between pointers and unsafe.Pointer.
  • between unsafe.Pointer and uintptr.
  • from (Unicode) integer to (UTF-8) string.

A conversion may imply a type name change also.

This operation cannot fail dynamically.

Conversions of untyped string/number/bool constants to a specific representation are eliminated during SSA construction.

Pos() returns the ast.CallExpr.Lparen, if the instruction arose from an explicit conversion in the source.

Example printed form: 

t1 = convert []byte <- string (t0)

func (*Convert) Name 

func (v *Convert) Name() string

func (*Convert) Operands 

func (v *Convert) Operands(rands []*Value) []*Value

func (*Convert) Pos 

func (v *Convert) Pos() token.Pos

func (*Convert) Referrers 

func (v *Convert) Referrers() *[]Instruction

func (*Convert) String 

func (v *Convert) String() string

func (*Convert) Type 

func (v *Convert) Type() types.Type

type DebugRef 

type DebugRef struct {
	Expr ast.Expr // the referring expression (never *ast.ParenExpr)

	IsAddr bool  // Expr is addressable and X is the address it denotes
	X      Value // the value or address of Expr
	// contains filtered or unexported fields
}

A DebugRef instruction maps a source-level expression Expr to the SSA value X that represents the value (!IsAddr) or address (IsAddr) of that expression.

DebugRef is a pseudo-instruction: it has no dynamic effect.

Pos() returns Expr.Pos(), the start position of the source-level expression. This is not the same as the "designated" token as documented at Value.Pos(). e.g. CallExpr.Pos() does not return the position of the ("designated") Lparen token.

If Expr is an *ast.Ident denoting a var or func, Object() returns the object; though this information can be obtained from the type checker, including it here greatly facilitates debugging. For non-Ident expressions, Object() returns nil.

DebugRefs are generated only for functions built with debugging enabled; see Package.SetDebugMode() and the GlobalDebug builder mode flag.

DebugRefs are not emitted for ast.Idents referring to constants or predeclared identifiers, since they are trivial and numerous. Nor are they emitted for ast.ParenExprs.

(By representing these as instructions, rather than out-of-band, consistency is maintained during transformation passes by the ordinary SSA renaming machinery.)

Example printed form: 

; *ast.CallExpr @ 102:9 is t5
; var x float64 @ 109:72 is x
; address of *ast.CompositeLit @ 216:10 is t0

func (*DebugRef) Block 

func (v *DebugRef) Block() *BasicBlock

func (*DebugRef) Operands 

func (s *DebugRef) Operands(rands []*Value) []*Value

func (*DebugRef) Parent 

func (v *DebugRef) Parent() *Function

func (*DebugRef) Pos 

func (s *DebugRef) Pos() token.Pos

func (*DebugRef) Referrers 

func (v *DebugRef) Referrers() *[]Instruction

func (*DebugRef) String 

func (s *DebugRef) String() string

type Defer 

type Defer struct {
	Call CallCommon
	// contains filtered or unexported fields
}

The Defer instruction pushes the specified call onto a stack of functions to be called by a RunDefers instruction or by a panic.

See CallCommon for generic function call documentation.

Pos() returns the ast.DeferStmt.Defer.

Example printed form: 

defer println(t0, t1)
defer t3()
defer invoke t5.Println(...t6)

func (*Defer) Block 

func (v *Defer) Block() *BasicBlock

func (*Defer) Common 

func (s *Defer) Common() *CallCommon

func (*Defer) Operands 

func (s *Defer) Operands(rands []*Value) []*Value

func (*Defer) Parent 

func (v *Defer) Parent() *Function

func (*Defer) Pos 

func (s *Defer) Pos() token.Pos

func (*Defer) Referrers 

func (v *Defer) Referrers() *[]Instruction

func (*Defer) String 

func (s *Defer) String() string

func (*Defer) Value 

func (s *Defer) Value() *Call

type Extract 

type Extract struct {
	Tuple Value
	Index int
	// contains filtered or unexported fields
}

The Extract instruction yields component Index of Tuple.

This is used to access the results of instructions with multiple return values, such as Call, TypeAssert, Next, UnOp(ARROW) and IndexExpr(Map).

Example printed form: 

t1 = extract t0 #1

func (*Extract) Name 

func (v *Extract) Name() string

func (*Extract) Operands 

func (v *Extract) Operands(rands []*Value) []*Value

func (*Extract) Pos 

func (v *Extract) Pos() token.Pos

func (*Extract) Referrers 

func (v *Extract) Referrers() *[]Instruction

func (*Extract) String 

func (v *Extract) String() string

func (*Extract) Type 

func (v *Extract) Type() types.Type

type Field 

type Field struct {
	X     Value // struct
	Field int   // index into X.Type().(*types.Struct).Fields
	// contains filtered or unexported fields
}

The Field instruction yields the Field of struct X.

The field is identified by its index within the field list of the struct type of X; by using numeric indices we avoid ambiguity of package-local identifiers and permit compact representations.

Pos() returns the position of the ast.SelectorExpr.Sel for the field, if explicit in the source.

Example printed form: 

t1 = t0.name [#1]

func (*Field) Name 

func (v *Field) Name() string

func (*Field) Operands 

func (v *Field) Operands(rands []*Value) []*Value

func (*Field) Pos 

func (v *Field) Pos() token.Pos

func (*Field) Referrers 

func (v *Field) Referrers() *[]Instruction

func (*Field) String 

func (v *Field) String() string

func (*Field) Type 

func (v *Field) Type() types.Type

type FieldAddr 

type FieldAddr struct {
	X     Value // *struct
	Field int   // index into X.Type().Deref().(*types.Struct).Fields
	// contains filtered or unexported fields
}

The FieldAddr instruction yields the address of Field of *struct X.

The field is identified by its index within the field list of the struct type of X.

Dynamically, this instruction panics if X evaluates to a nil pointer.

Type() returns a (possibly named) *types.Pointer.

Pos() returns the position of the ast.SelectorExpr.Sel for the field, if explicit in the source.

Example printed form: 

t1 = &t0.name [#1]

func (*FieldAddr) Name 

func (v *FieldAddr) Name() string

func (*FieldAddr) Operands 

func (v *FieldAddr) Operands(rands []*Value) []*Value

func (*FieldAddr) Pos 

func (v *FieldAddr) Pos() token.Pos

func (*FieldAddr) Referrers 

func (v *FieldAddr) Referrers() *[]Instruction

func (*FieldAddr) String 

func (v *FieldAddr) String() string

func (*FieldAddr) Type 

func (v *FieldAddr) Type() types.Type

type FreeVar 

type FreeVar struct {
	// contains filtered or unexported fields
}

A FreeVar represents a free variable of the function to which it belongs.

FreeVars are used to implement anonymous functions, whose free variables are lexically captured in a closure formed by MakeClosure. The value of such a free var is an Alloc or another FreeVar and is considered a potentially escaping heap address, with pointer type.

FreeVars are also used to implement bound method closures. Such a free var represents the receiver value and may be of any type that has concrete methods.

Pos() returns the position of the value that was captured, which belongs to an enclosing function.

func (*FreeVar) Name 

func (v *FreeVar) Name() string

func (*FreeVar) Operands 

func (v *FreeVar) Operands(rands []*Value) []*Value

func (*FreeVar) Parent 

func (v *FreeVar) Parent() *Function

func (*FreeVar) Pos 

func (v *FreeVar) Pos() token.Pos

func (*FreeVar) Referrers 

func (v *FreeVar) Referrers() *[]Instruction

func (*FreeVar) String 

func (v *FreeVar) String() string

func (*FreeVar) Type 

func (v *FreeVar) Type() types.Type

type Function 

type Function struct {
	Signature *types.Signature

	Synthetic string // provenance of synthetic function; "" for true source functions

	Pkg       *Package      // enclosing package; nil for shared funcs (wrappers and error.Error)
	Prog      *Program      // enclosing program
	Params    []*Parameter  // function parameters; for methods, includes receiver
	FreeVars  []*FreeVar    // free variables whose values must be supplied by closure
	Locals    []*Alloc      // local variables of this function
	Blocks    []*BasicBlock // basic blocks of the function; nil => external
	Recover   *BasicBlock   // optional; control transfers here after recovered panic
	AnonFuncs []*Function   // anonymous functions directly beneath this one
	// contains filtered or unexported fields
}

Function represents the parameters, results, and code of a function or method.

If Blocks is nil, this indicates an external function for which no Go source code is available. In this case, FreeVars and Locals are nil too. Clients performing whole-program analysis must handle external functions specially.

Blocks contains the function's control-flow graph (CFG). Blocks[0] is the function entry point; block order is not otherwise semantically significant, though it may affect the readability of the disassembly. To iterate over the blocks in dominance order, use DomPreorder().

Recover is an optional second entry point to which control resumes after a recovered panic. The Recover block may contain only a return statement, preceded by a load of the function's named return parameters, if any.

A nested function (Parent()!=nil) that refers to one or more lexically enclosing local variables ("free variables") has FreeVars. Such functions cannot be called directly but require a value created by MakeClosure which, via its Bindings, supplies values for these parameters.

If the function is a method (Signature.Recv() != nil) then the first element of Params is the receiver parameter.

A Go package may declare many functions called "init". For each one, Object().Name() returns "init" but Name() returns "init#1", etc, in declaration order.

Pos() returns the declaring ast.FuncLit.Type.Func or the position of the ast.FuncDecl.Name, if the function was explicit in the source. Synthetic wrappers, for which Synthetic != "", may share the same position as the function they wrap. Syntax.Pos() always returns the position of the declaring "func" token.

Type() returns the function's Signature.

func EnclosingFunction 

func EnclosingFunction(pkg *Package, path []ast.Node) *Function

EnclosingFunction returns the function that contains the syntax node denoted by path.

Syntax associated with package-level variable specifications is enclosed by the package's init() function.

Returns nil if not found; reasons might include:

  • the node is not enclosed by any function.
  • the node is within an anonymous function (FuncLit) and its SSA function has not been created yet (pkg.Build() has not yet been called).

func (*Function) DomPreorder 

func (f *Function) DomPreorder() []*BasicBlock

DomPreorder returns a new slice containing the blocks of f in dominator tree preorder.

func (*Function) Name 

func (v *Function) Name() string

func (*Function) Object 

func (v *Function) Object() types.Object

func (*Function) Operands 

func (v *Function) Operands(rands []*Value) []*Value

func (*Function) Package 

func (v *Function) Package() *Package

func (*Function) Parent 

func (v *Function) Parent() *Function

func (*Function) Pos 

func (v *Function) Pos() token.Pos

func (*Function) Referrers 

func (v *Function) Referrers() *[]Instruction

func (*Function) RelString 

func (f *Function) RelString(from *types.Package) string

RelString returns the full name of this function, qualified by package name, receiver type, etc.

The specific formatting rules are not guaranteed and may change.

Examples: 

"math.IsNaN"                  // a package-level function
"(*bytes.Buffer).Bytes"       // a declared method or a wrapper
"(*bytes.Buffer).Bytes$thunk" // thunk (func wrapping method; receiver is param 0)
"(*bytes.Buffer).Bytes$bound" // bound (func wrapping method; receiver supplied by closure)
"main.main$1"                 // an anonymous function in main
"main.init#1"                 // a declared init function
"main.init"                   // the synthesized package initializer

When these functions are referred to from within the same package (i.e. from == f.Pkg.Object), they are rendered without the package path. For example: "IsNaN", "(*Buffer).Bytes", etc.

All non-synthetic functions have distinct package-qualified names. (But two methods may have the same name "(T).f" if one is a synthetic wrapper promoting a non-exported method "f" from another package; in that case, the strings are equal but the identifiers "f" are distinct.)

func (*Function) RemoveNilBlocks 

func (f *Function) RemoveNilBlocks()

func (*Function) String 

func (v *Function) String() string

func (*Function) Syntax 

func (f *Function) Syntax() ast.Node

Syntax returns an ast.Node whose Pos/End methods provide the lexical extent of the function if it was defined by Go source code (f.Synthetic==""), or nil otherwise.

If f was built with debug information (see Package.SetDebugRef), the result is the *ast.FuncDecl or *ast.FuncLit that declared the function. Otherwise, it is an opaque Node providing only position information; this avoids pinning the AST in memory.

func (*Function) Token 

func (v *Function) Token() token.Token

func (*Function) Type 

func (v *Function) Type() types.Type

func (*Function) ValueForExpr 

func (f *Function) ValueForExpr(e ast.Expr) (value Value, isAddr bool)

ValueForExpr returns the SSA Value that corresponds to non-constant expression e.

It returns nil if no value was found, e.g.

  • the expression is not lexically contained within f;
  • f was not built with debug information; or
  • e is a constant expression. (For efficiency, no debug information is stored for constants. Use go/types.Info.Types[e].Value instead.)
  • e is a reference to nil or a built-in function.
  • the value was optimised away.

If e is an addressable expression used in an lvalue context, value is the address denoted by e, and isAddr is true.

The types of e (or &e, if isAddr) and the result are equal (modulo "untyped" bools resulting from comparisons).

(Tip: to find the ssa.Value given a source position, use importer.PathEnclosingInterval to locate the ast.Node, then EnclosingFunction to locate the Function, then ValueForExpr to find the ssa.Value.)

func (*Function) WriteTo 

func (f *Function) WriteTo(w io.Writer) (int64, error)

type Global 

type Global struct {
	Pkg *Package
	// contains filtered or unexported fields
}

A Global is a named Value holding the address of a package-level variable.

Pos() returns the position of the ast.ValueSpec.Names[*] identifier.

func (*Global) Name 

func (v *Global) Name() string

func (*Global) Object 

func (v *Global) Object() types.Object

func (*Global) Operands 

func (v *Global) Operands(rands []*Value) []*Value

func (*Global) Package 

func (v *Global) Package() *Package

func (*Global) Parent 

func (v *Global) Parent() *Function

func (*Global) Pos 

func (v *Global) Pos() token.Pos

func (*Global) Referrers 

func (v *Global) Referrers() *[]Instruction

func (*Global) RelString 

func (v *Global) RelString(from *types.Package) string

func (*Global) String 

func (v *Global) String() string

func (*Global) Token 

func (v *Global) Token() token.Token

func (*Global) Type 

func (v *Global) Type() types.Type

type Go 

type Go struct {
	Call CallCommon
	// contains filtered or unexported fields
}

The Go instruction creates a new goroutine and calls the specified function within it.

See CallCommon for generic function call documentation.

Pos() returns the ast.GoStmt.Go.

Example printed form: 

go println(t0, t1)
go t3()
go invoke t5.Println(...t6)

func (*Go) Block 

func (v *Go) Block() *BasicBlock

func (*Go) Common 

func (s *Go) Common() *CallCommon

func (*Go) Operands 

func (s *Go) Operands(rands []*Value) []*Value

func (*Go) Parent 

func (v *Go) Parent() *Function

func (*Go) Pos 

func (s *Go) Pos() token.Pos

func (*Go) Referrers 

func (v *Go) Referrers() *[]Instruction

func (*Go) String 

func (s *Go) String() string

func (*Go) Value 

func (s *Go) Value() *Call

type If 

type If struct {
	Cond Value
	// contains filtered or unexported fields
}

The If instruction transfers control to one of the two successors of its owning block, depending on the boolean Cond: the first if true, the second if false.

An If instruction must be the last instruction of its containing BasicBlock.

Pos() returns NoPos.

Example printed form: 

if t0 goto done else body

func (*If) Block 

func (v *If) Block() *BasicBlock

func (*If) Operands 

func (s *If) Operands(rands []*Value) []*Value

func (*If) Parent 

func (v *If) Parent() *Function

func (*If) Pos 

func (s *If) Pos() token.Pos

func (*If) Referrers 

func (v *If) Referrers() *[]Instruction

func (*If) String 

func (s *If) String() string

type Index 

type Index struct {
	X     Value // array
	Index Value // integer index
	// contains filtered or unexported fields
}

The Index instruction yields element Index of array X.

Pos() returns the ast.IndexExpr.Lbrack for the index operation, if explicit in the source.

Example printed form: 

t2 = t0[t1]

func (*Index) Name 

func (v *Index) Name() string

func (*Index) Operands 

func (v *Index) Operands(rands []*Value) []*Value

func (*Index) Pos 

func (v *Index) Pos() token.Pos

func (*Index) Referrers 

func (v *Index) Referrers() *[]Instruction

func (*Index) String 

func (v *Index) String() string

func (*Index) Type 

func (v *Index) Type() types.Type

type IndexAddr 

type IndexAddr struct {
	X     Value // slice or *array,
	Index Value // numeric index
	// contains filtered or unexported fields
}

The IndexAddr instruction yields the address of the element at index Index of collection X. Index is an integer expression.

The elements of maps and strings are not addressable; use Lookup or MapUpdate instead.

Dynamically, this instruction panics if X evaluates to a nil *array pointer.

Type() returns a (possibly named) *types.Pointer.

Pos() returns the ast.IndexExpr.Lbrack for the index operation, if explicit in the source.

Example printed form: 

t2 = &t0[t1]

func (*IndexAddr) Name 

func (v *IndexAddr) Name() string

func (*IndexAddr) Operands 

func (v *IndexAddr) Operands(rands []*Value) []*Value

func (*IndexAddr) Pos 

func (v *IndexAddr) Pos() token.Pos

func (*IndexAddr) Referrers 

func (v *IndexAddr) Referrers() *[]Instruction

func (*IndexAddr) String 

func (v *IndexAddr) String() string

func (*IndexAddr) Type 

func (v *IndexAddr) Type() types.Type

type Instruction 

type Instruction interface {
	// String returns the disassembled form of this value.
	//
	// Examples of Instructions that are Values:
	//       "x + y"     (BinOp)
	//       "len([])"   (Call)
	// Note that the name of the Value is not printed.
	//
	// Examples of Instructions that are not Values:
	//       "return x"  (Return)
	//       "*y = x"    (Store)
	//
	// (The separation Value.Name() from Value.String() is useful
	// for some analyses which distinguish the operation from the
	// value it defines, e.g., 'y = local int' is both an allocation
	// of memory 'local int' and a definition of a pointer y.)
	String() string

	// Parent returns the function to which this instruction
	// belongs.
	Parent() *Function

	// Block returns the basic block to which this instruction
	// belongs.
	Block() *BasicBlock

	// Operands returns the operands of this instruction: the
	// set of Values it references.
	//
	// Specifically, it appends their addresses to rands, a
	// user-provided slice, and returns the resulting slice,
	// permitting avoidance of memory allocation.
	//
	// The operands are appended in undefined order, but the order
	// is consistent for a given Instruction; the addresses are
	// always non-nil but may point to a nil Value.  Clients may
	// store through the pointers, e.g. to effect a value
	// renaming.
	//
	// Value.Referrers is a subset of the inverse of this
	// relation.  (Referrers are not tracked for all types of
	// Values.)
	Operands(rands []*Value) []*Value

	// Pos returns the location of the AST token most closely
	// associated with the operation that gave rise to this
	// instruction, or token.NoPos if it was not explicit in the
	// source.
	//
	// For each ast.Node type, a particular token is designated as
	// the closest location for the expression, e.g. the Go token
	// for an *ast.GoStmt.  This permits a compact but approximate
	// mapping from Instructions to source positions for use in
	// diagnostic messages, for example.
	//
	// (Do not use this position to determine which Instruction
	// corresponds to an ast.Expr; see the notes for Value.Pos.
	// This position may be used to determine which non-Value
	// Instruction corresponds to some ast.Stmts, but not all: If
	// and Jump instructions have no Pos(), for example.)
	Pos() token.Pos
	// contains filtered or unexported methods
}

An Instruction is an SSA instruction that computes a new Value or has some effect.

An Instruction that defines a value (e.g. BinOp) also implements the Value interface; an Instruction that only has an effect (e.g. Store) does not.

func RemoveInstr 

func RemoveInstr(refs []Instruction, instr Instruction) []Instruction

type Jump 

type Jump struct {
	// contains filtered or unexported fields
}

The Jump instruction transfers control to the sole successor of its owning block.

A Jump must be the last instruction of its containing BasicBlock.

Pos() returns NoPos.

Example printed form: 

jump done

func NewJump 

func NewJump(parent *BasicBlock) *Jump

func (*Jump) Block 

func (v *Jump) Block() *BasicBlock

func (*Jump) Operands 

func (*Jump) Operands(rands []*Value) []*Value

func (*Jump) Parent 

func (v *Jump) Parent() *Function

func (*Jump) Pos 

func (s *Jump) Pos() token.Pos

func (*Jump) Referrers 

func (v *Jump) Referrers() *[]Instruction

func (*Jump) String 

func (s *Jump) String() string

type Lookup 

type Lookup struct {
	X       Value // string or map
	Index   Value // numeric or key-typed index
	CommaOk bool  // return a value,ok pair
	// contains filtered or unexported fields
}

The Lookup instruction yields element Index of collection X, a map or string. Index is an integer expression if X is a string or the appropriate key type if X is a map.

If CommaOk, the result is a 2-tuple of the value above and a boolean indicating the result of a map membership test for the key. The components of the tuple are accessed using Extract.

Pos() returns the ast.IndexExpr.Lbrack, if explicit in the source.

Example printed form: 

t2 = t0[t1]
t5 = t3[t4],ok

func (*Lookup) Name 

func (v *Lookup) Name() string

func (*Lookup) Operands 

func (v *Lookup) Operands(rands []*Value) []*Value

func (*Lookup) Pos 

func (v *Lookup) Pos() token.Pos

func (*Lookup) Referrers 

func (v *Lookup) Referrers() *[]Instruction

func (*Lookup) String 

func (v *Lookup) String() string

func (*Lookup) Type 

func (v *Lookup) Type() types.Type

type MakeChan 

type MakeChan struct {
	Size Value // int; size of buffer; zero => synchronous.
	// contains filtered or unexported fields
}

The MakeChan instruction creates a new channel object and yields a value of kind chan.

Type() returns a (possibly named) *types.Chan.

Pos() returns the ast.CallExpr.Lparen for the make(chan) that created it.

Example printed form: 

t0 = make chan int 0
t0 = make IntChan 0

func (*MakeChan) Name 

func (v *MakeChan) Name() string

func (*MakeChan) Operands 

func (v *MakeChan) Operands(rands []*Value) []*Value

func (*MakeChan) Pos 

func (v *MakeChan) Pos() token.Pos

func (*MakeChan) Referrers 

func (v *MakeChan) Referrers() *[]Instruction

func (*MakeChan) String 

func (v *MakeChan) String() string

func (*MakeChan) Type 

func (v *MakeChan) Type() types.Type

type MakeClosure 

type MakeClosure struct {
	Fn       Value   // always a *Function
	Bindings []Value // values for each free variable in Fn.FreeVars
	// contains filtered or unexported fields
}

The MakeClosure instruction yields a closure value whose code is Fn and whose free variables' values are supplied by Bindings.

Type() returns a (possibly named) *types.Signature.

Pos() returns the ast.FuncLit.Type.Func for a function literal closure or the ast.SelectorExpr.Sel for a bound method closure.

Example printed form: 

t0 = make closure anon@1.2 [x y z]
t1 = make closure bound$(main.I).add [i]

func (*MakeClosure) Name 

func (v *MakeClosure) Name() string

func (*MakeClosure) Operands 

func (v *MakeClosure) Operands(rands []*Value) []*Value

func (*MakeClosure) Pos 

func (v *MakeClosure) Pos() token.Pos

func (*MakeClosure) Referrers 

func (v *MakeClosure) Referrers() *[]Instruction

func (*MakeClosure) String 

func (v *MakeClosure) String() string

func (*MakeClosure) Type 

func (v *MakeClosure) Type() types.Type

type MakeInterface 

type MakeInterface struct {
	X Value
	// contains filtered or unexported fields
}

MakeInterface constructs an instance of an interface type from a value of a concrete type.

Use Program.MethodSets.MethodSet(X.Type()) to find the method-set of X, and Program.Method(m) to find the implementation of a method.

To construct the zero value of an interface type T, use: 

NewConst(exact.MakeNil(), T, pos)

Pos() returns the ast.CallExpr.Lparen, if the instruction arose from an explicit conversion in the source.

Example printed form: 

t1 = make interface{} <- int (42:int)
t2 = make Stringer <- t0

func (*MakeInterface) Name 

func (v *MakeInterface) Name() string

func (*MakeInterface) Operands 

func (v *MakeInterface) Operands(rands []*Value) []*Value

func (*MakeInterface) Pos 

func (v *MakeInterface) Pos() token.Pos

func (*MakeInterface) Referrers 

func (v *MakeInterface) Referrers() *[]Instruction

func (*MakeInterface) String 

func (v *MakeInterface) String() string

func (*MakeInterface) Type 

func (v *MakeInterface) Type() types.Type

type MakeMap 

type MakeMap struct {
	Reserve Value // initial space reservation; nil => default
	// contains filtered or unexported fields
}

The MakeMap instruction creates a new hash-table-based map object and yields a value of kind map.

Type() returns a (possibly named) *types.Map.

Pos() returns the ast.CallExpr.Lparen, if created by make(map), or the ast.CompositeLit.Lbrack if created by a literal.

Example printed form: 

t1 = make map[string]int t0
t1 = make StringIntMap t0

func (*MakeMap) Name 

func (v *MakeMap) Name() string

func (*MakeMap) Operands 

func (v *MakeMap) Operands(rands []*Value) []*Value

func (*MakeMap) Pos 

func (v *MakeMap) Pos() token.Pos

func (*MakeMap) Referrers 

func (v *MakeMap) Referrers() *[]Instruction

func (*MakeMap) String 

func (v *MakeMap) String() string

func (*MakeMap) Type 

func (v *MakeMap) Type() types.Type

type MakeSlice 

type MakeSlice struct {
	Len Value
	Cap Value
	// contains filtered or unexported fields
}

The MakeSlice instruction yields a slice of length Len backed by a newly allocated array of length Cap.

Both Len and Cap must be non-nil Values of integer type.

(Alloc(types.Array) followed by Slice will not suffice because Alloc can only create arrays of constant length.)

Type() returns a (possibly named) *types.Slice.

Pos() returns the ast.CallExpr.Lparen for the make([]T) that created it.

Example printed form: 

t1 = make []string 1:int t0
t1 = make StringSlice 1:int t0

func (*MakeSlice) Name 

func (v *MakeSlice) Name() string

func (*MakeSlice) Operands 

func (v *MakeSlice) Operands(rands []*Value) []*Value

func (*MakeSlice) Pos 

func (v *MakeSlice) Pos() token.Pos

func (*MakeSlice) Referrers 

func (v *MakeSlice) Referrers() *[]Instruction

func (*MakeSlice) String 

func (v *MakeSlice) String() string

func (*MakeSlice) Type 

func (v *MakeSlice) Type() types.Type

type MapUpdate 

type MapUpdate struct {
	Map   Value
	Key   Value
	Value Value
	// contains filtered or unexported fields
}

The MapUpdate instruction updates the association of Map[Key] to Value.

Pos() returns the ast.KeyValueExpr.Colon or ast.IndexExpr.Lbrack, if explicit in the source.

Example printed form: 

t0[t1] = t2

func (*MapUpdate) Block 

func (v *MapUpdate) Block() *BasicBlock

func (*MapUpdate) Operands 

func (v *MapUpdate) Operands(rands []*Value) []*Value

func (*MapUpdate) Parent 

func (v *MapUpdate) Parent() *Function

func (*MapUpdate) Pos 

func (s *MapUpdate) Pos() token.Pos

func (*MapUpdate) Referrers 

func (v *MapUpdate) Referrers() *[]Instruction

func (*MapUpdate) String 

func (s *MapUpdate) String() string

type Member 

type Member interface {
	Name() string                    // declared name of the package member
	String() string                  // package-qualified name of the package member
	RelString(*types.Package) string // like String, but relative refs are unqualified
	Object() types.Object            // typechecker's object for this member, if any
	Pos() token.Pos                  // position of member's declaration, if known
	Type() types.Type                // type of the package member
	Token() token.Token              // token.{VAR,FUNC,CONST,TYPE}
	Package() *Package               // the containing package
}

A Member is a member of a Go package, implemented by *NamedConst, *Global, *Function, or *Type; they are created by package-level const, var, func and type declarations respectively.

type NamedConst 

type NamedConst struct {
	Value *Const
	// contains filtered or unexported fields
}

A NamedConst is a Member of a Package representing a package-level named constant.

Pos() returns the position of the declaring ast.ValueSpec.Names[*] identifier.

NB: a NamedConst is not a Value; it contains a constant Value, which it augments with the name and position of its 'const' declaration.

func (*NamedConst) Name 

func (c *NamedConst) Name() string

func (*NamedConst) Object 

func (c *NamedConst) Object() types.Object

func (*NamedConst) Package 

func (c *NamedConst) Package() *Package

func (*NamedConst) Pos 

func (c *NamedConst) Pos() token.Pos

func (*NamedConst) RelString 

func (c *NamedConst) RelString(from *types.Package) string

func (*NamedConst) String 

func (c *NamedConst) String() string

func (*NamedConst) Token 

func (c *NamedConst) Token() token.Token

func (*NamedConst) Type 

func (c *NamedConst) Type() types.Type

type Next 

type Next struct {
	Iter     Value
	IsString bool // true => string iterator; false => map iterator.
	// contains filtered or unexported fields
}

The Next instruction reads and advances the (map or string) iterator Iter and returns a 3-tuple value (ok, k, v). If the iterator is not exhausted, ok is true and k and v are the next elements of the domain and range, respectively. Otherwise ok is false and k and v are undefined.

Components of the tuple are accessed using Extract.

The IsString field distinguishes iterators over strings from those over maps, as the Type() alone is insufficient: consider map[int]rune.

Type() returns a *types.Tuple for the triple (ok, k, v). The types of k and/or v may be types.Invalid.

Example printed form: 

t1 = next t0

func (*Next) Name 

func (v *Next) Name() string

func (*Next) Operands 

func (v *Next) Operands(rands []*Value) []*Value

func (*Next) Pos 

func (v *Next) Pos() token.Pos

func (*Next) Referrers 

func (v *Next) Referrers() *[]Instruction

func (*Next) String 

func (v *Next) String() string

func (*Next) Type 

func (v *Next) Type() types.Type

type Node 

type Node interface {
	// Common methods:
	String() string
	Pos() token.Pos
	Parent() *Function

	// Partial methods:
	Operands(rands []*Value) []*Value // nil for non-Instructions
	Referrers() *[]Instruction        // nil for non-Values
}

A Node is a node in the SSA value graph. Every concrete type that implements Node is also either a Value, an Instruction, or both.

Node contains the methods common to Value and Instruction, plus the Operands and Referrers methods generalized to return nil for non-Instructions and non-Values, respectively.

Node is provided to simplify SSA graph algorithms. Clients should use the more specific and informative Value or Instruction interfaces where appropriate.

type Package 

type Package struct {
	Prog    *Program          // the owning program
	Pkg     *types.Package    // the corresponding go/types.Package
	Members map[string]Member // all package members keyed by name (incl. init and init#%d)
	// contains filtered or unexported fields
}

A Package is a single analyzed Go package containing Members for all package-level functions, variables, constants and types it declares. These may be accessed directly via Members, or via the type-specific accessor methods Func, Type, Var and Const.

Members also contains entries for "init" (the synthetic package initializer) and "init#%d", the nth declared init function, and unspecified other things too.

func (*Package) Build 

func (p *Package) Build()

Build builds SSA code for all functions and vars in package p.

Precondition: CreatePackage must have been called for all of p's direct imports (and hence its direct imports must have been error-free).

Build is idempotent and thread-safe.

func (*Package) Const 

func (p *Package) Const(name string) (c *NamedConst)

Const returns the package-level constant of the specified name, or nil if not found.

func (*Package) Func 

func (p *Package) Func(name string) (f *Function)

Func returns the package-level function of the specified name, or nil if not found.

func (*Package) SetDebugMode 

func (pkg *Package) SetDebugMode(debug bool)

SetDebugMode sets the debug mode for package pkg. If true, all its functions will include full debug info. This greatly increases the size of the instruction stream, and causes Functions to depend upon the ASTs, potentially keeping them live in memory for longer.

func (*Package) String 

func (p *Package) String() string

func (*Package) Type 

func (p *Package) Type(name string) (t *Type)

Type returns the package-level type of the specified name, or nil if not found.

func (*Package) Var 

func (p *Package) Var(name string) (g *Global)

Var returns the package-level variable of the specified name, or nil if not found.

func (*Package) WriteTo 

func (p *Package) WriteTo(w io.Writer) (int64, error)

type Panic 

type Panic struct {
	X Value // an interface{}
	// contains filtered or unexported fields
}

The Panic instruction initiates a panic with value X.

A Panic instruction must be the last instruction of its containing BasicBlock, which must have no successors.

NB: 'go panic(x)' and 'defer panic(x)' do not use this instruction; they are treated as calls to a built-in function.

Pos() returns the ast.CallExpr.Lparen if this panic was explicit in the source.

Example printed form: 

panic t0

func (*Panic) Block 

func (v *Panic) Block() *BasicBlock

func (*Panic) Operands 

func (s *Panic) Operands(rands []*Value) []*Value

func (*Panic) Parent 

func (v *Panic) Parent() *Function

func (*Panic) Pos 

func (s *Panic) Pos() token.Pos

func (*Panic) Referrers 

func (v *Panic) Referrers() *[]Instruction

func (*Panic) String 

func (s *Panic) String() string

type Parameter 

type Parameter struct {
	// contains filtered or unexported fields
}

A Parameter represents an input parameter of a function.

func (*Parameter) Name 

func (v *Parameter) Name() string

func (*Parameter) Object 

func (v *Parameter) Object() types.Object

func (*Parameter) Operands 

func (v *Parameter) Operands(rands []*Value) []*Value

func (*Parameter) Parent 

func (v *Parameter) Parent() *Function

func (*Parameter) Pos 

func (v *Parameter) Pos() token.Pos

func (*Parameter) Referrers 

func (v *Parameter) Referrers() *[]Instruction

func (*Parameter) String 

func (v *Parameter) String() string

func (*Parameter) Type 

func (v *Parameter) Type() types.Type

type Phi 

type Phi struct {
	Comment string  // a hint as to its purpose
	Edges   []Value // Edges[i] is value for Block().Preds[i]
	// contains filtered or unexported fields
}

The Phi instruction represents an SSA φ-node, which combines values that differ across incoming control-flow edges and yields a new value. Within a block, all φ-nodes must appear before all non-φ nodes.

Pos() returns the position of the && or || for short-circuit control-flow joins, or that of the *Alloc for φ-nodes inserted during SSA renaming.

Example printed form: 

t2 = phi [0: t0, 1: t1]

func (*Phi) Name 

func (v *Phi) Name() string

func (*Phi) Operands 

func (v *Phi) Operands(rands []*Value) []*Value

func (*Phi) Pos 

func (v *Phi) Pos() token.Pos

func (*Phi) Referrers 

func (v *Phi) Referrers() *[]Instruction

func (*Phi) String 

func (v *Phi) String() string

func (*Phi) Type 

func (v *Phi) Type() types.Type

type Program 

type Program struct {
	Fset *token.FileSet // position information for the files of this Program

	MethodSets typeutil.MethodSetCache // cache of type-checker's method-sets
	// contains filtered or unexported fields
}

A Program is a partial or complete Go program converted to SSA form.

func NewProgram 

func NewProgram(fset *token.FileSet, mode BuilderMode) *Program

NewProgram returns a new SSA Program.

mode controls diagnostics and checking during SSA construction.

func (*Program) AllPackages 

func (prog *Program) AllPackages() []*Package

AllPackages returns a new slice containing all packages in the program prog in unspecified order.

func (*Program) Build 

func (prog *Program) Build()

Build calls Package.Build for each package in prog. Building occurs in parallel unless the BuildSerially mode flag was set.

Build is intended for whole-program analysis; a typical compiler need only build a single package.

Build is idempotent and thread-safe.

func (*Program) ConstValue 

func (prog *Program) ConstValue(obj *types.Const) *Const

ConstValue returns the SSA Value denoted by the source-level named constant obj.

func (*Program) CreatePackage 

func (prog *Program) CreatePackage(pkg *types.Package, files []*ast.File, info *types.Info, importable bool) *Package

CreatePackage constructs and returns an SSA Package from the specified type-checked, error-free file ASTs, and populates its Members mapping.

importable determines whether this package should be returned by a subsequent call to ImportedPackage(pkg.Path()).

The real work of building SSA form for each function is not done until a subsequent call to Package.Build().

func (*Program) CreateTestMainPackage 

func (prog *Program) CreateTestMainPackage(pkg *Package) *Package

CreateTestMainPackage creates and returns a synthetic "testmain" package for the specified package if it defines tests, benchmarks or executable examples, or nil otherwise. The new package is named "main" and provides a function named "main" that runs the tests, similar to the one that would be created by the 'go test' tool.

Subsequent calls to prog.AllPackages include the new package. The package pkg must belong to the program prog.

func (*Program) FuncValue 

func (prog *Program) FuncValue(obj *types.Func) *Function

FuncValue returns the concrete Function denoted by the source-level named function obj, or nil if obj denotes an interface method.

TODO(adonovan): check the invariant that obj.Type() matches the result's Signature, both in the params/results and in the receiver.

func (*Program) ImportedPackage 

func (prog *Program) ImportedPackage(path string) *Package

ImportedPackage returns the importable SSA Package whose import path is path, or nil if no such SSA package has been created.

Not all packages are importable. For example, no import declaration can resolve to the x_test package created by 'go test' or the ad-hoc main package created 'go build foo.go'.

func (*Program) LookupMethod 

func (prog *Program) LookupMethod(T types.Type, pkg *types.Package, name string) *Function

LookupMethod returns the implementation of the method of type T identified by (pkg, name). It returns nil if the method exists but is abstract, and panics if T has no such method.

func (*Program) MethodValue 

func (prog *Program) MethodValue(sel *types.Selection) *Function

MethodValue returns the Function implementing method sel, building wrapper methods on demand. It returns nil if sel denotes an abstract (interface) method.

Precondition: sel.Kind() == MethodVal.

Thread-safe.

EXCLUSIVE_LOCKS_ACQUIRED(prog.methodsMu)

func (*Program) NewFunction 

func (prog *Program) NewFunction(name string, sig *types.Signature, provenance string) *Function

NewFunction returns a new synthetic Function instance belonging to prog, with its name and signature fields set as specified.

The caller is responsible for initializing the remaining fields of the function object, e.g. Pkg, Params, Blocks.

It is practically impossible for clients to construct well-formed SSA functions/packages/programs directly, so we assume this is the job of the Builder alone. NewFunction exists to provide clients a little flexibility. For example, analysis tools may wish to construct fake Functions for the root of the callgraph, a fake "reflect" package, etc.

TODO(adonovan): think harder about the API here.

func (*Program) Package 

func (prog *Program) Package(obj *types.Package) *Package

Package returns the SSA Package corresponding to the specified type-checker package object. It returns nil if no such SSA package has been created.

func (*Program) RuntimeTypes 

func (prog *Program) RuntimeTypes() []types.Type

RuntimeTypes returns a new unordered slice containing all concrete types in the program for which a complete (non-empty) method set is required at run-time.

Thread-safe.

EXCLUSIVE_LOCKS_ACQUIRED(prog.methodsMu)

func (*Program) VarValue 

func (prog *Program) VarValue(obj *types.Var, pkg *Package, ref []ast.Node) (value Value, isAddr bool)

VarValue returns the SSA Value that corresponds to a specific identifier denoting the source-level named variable obj.

VarValue returns nil if a local variable was not found, perhaps because its package was not built, the debug information was not requested during SSA construction, or the value was optimized away.

ref is the path to an ast.Ident (e.g. from PathEnclosingInterval), and that ident must resolve to obj.

pkg is the package enclosing the reference. (A reference to a var always occurs within a function, so we need to know where to find it.)

If the identifier is a field selector and its base expression is non-addressable, then VarValue returns the value of that field. For example: 

func f() struct {x int}
f().x  // VarValue(x) returns a *Field instruction of type int

All other identifiers denote addressable locations (variables). For them, VarValue may return either the variable's address or its value, even when the expression is evaluated only for its value; the situation is reported by isAddr, the second component of the result.

If !isAddr, the returned value is the one associated with the specific identifier. For example, 

var x int    // VarValue(x) returns Const 0 here
x = 1        // VarValue(x) returns Const 1 here

It is not specified whether the value or the address is returned in any particular case, as it may depend upon optimizations performed during SSA code generation, such as registerization, constant folding, avoidance of materialization of subexpressions, etc.

type Range 

type Range struct {
	X Value // string or map
	// contains filtered or unexported fields
}

The Range instruction yields an iterator over the domain and range of X, which must be a string or map.

Elements are accessed via Next.

Type() returns an opaque and degenerate "rangeIter" type.

Pos() returns the ast.RangeStmt.For.

Example printed form: 

t0 = range "hello":string

func (*Range) Name 

func (v *Range) Name() string

func (*Range) Operands 

func (v *Range) Operands(rands []*Value) []*Value

func (*Range) Pos 

func (v *Range) Pos() token.Pos

func (*Range) Referrers 

func (v *Range) Referrers() *[]Instruction

func (*Range) String 

func (v *Range) String() string

func (*Range) Type 

func (v *Range) Type() types.Type

type Return 

type Return struct {
	Results []Value
	// contains filtered or unexported fields
}

The Return instruction returns values and control back to the calling function.

len(Results) is always equal to the number of results in the function's signature.

If len(Results) > 1, Return returns a tuple value with the specified components which the caller must access using Extract instructions.

There is no instruction to return a ready-made tuple like those returned by a "value,ok"-mode TypeAssert, Lookup or UnOp(ARROW) or a tail-call to a function with multiple result parameters.

Return must be the last instruction of its containing BasicBlock. Such a block has no successors.

Pos() returns the ast.ReturnStmt.Return, if explicit in the source.

Example printed form: 

return
return nil:I, 2:int

func (*Return) Block 

func (v *Return) Block() *BasicBlock

func (*Return) Operands 

func (s *Return) Operands(rands []*Value) []*Value

func (*Return) Parent 

func (v *Return) Parent() *Function

func (*Return) Pos 

func (s *Return) Pos() token.Pos

func (*Return) Referrers 

func (v *Return) Referrers() *[]Instruction

func (*Return) String 

func (s *Return) String() string

type RunDefers 

type RunDefers struct {
	// contains filtered or unexported fields
}

The RunDefers instruction pops and invokes the entire stack of procedure calls pushed by Defer instructions in this function.

It is legal to encounter multiple 'rundefers' instructions in a single control-flow path through a function; this is useful in the combined init() function, for example.

Pos() returns NoPos.

Example printed form: 

rundefers

func (*RunDefers) Block 

func (v *RunDefers) Block() *BasicBlock

func (*RunDefers) Operands 

func (*RunDefers) Operands(rands []*Value) []*Value

func (*RunDefers) Parent 

func (v *RunDefers) Parent() *Function

func (*RunDefers) Pos 

func (s *RunDefers) Pos() token.Pos

func (*RunDefers) Referrers 

func (v *RunDefers) Referrers() *[]Instruction

func (*RunDefers) String 

func (*RunDefers) String() string

type Select 

type Select struct {
	States   []*SelectState
	Blocking bool
	// contains filtered or unexported fields
}

The Select instruction tests whether (or blocks until) one of the specified sent or received states is entered.

Let n be the number of States for which Dir==RECV and T_i (0<=i<n) be the element type of each such state's Chan. Select returns an n+2-tuple 

(index int, recvOk bool, r_0 T_0, ... r_n-1 T_n-1)

The tuple's components, described below, must be accessed via the Extract instruction.

If Blocking, select waits until exactly one state holds, i.e. a channel becomes ready for the designated operation of sending or receiving; select chooses one among the ready states pseudorandomly, performs the send or receive operation, and sets 'index' to the index of the chosen channel.

If !Blocking, select doesn't block if no states hold; instead it returns immediately with index equal to -1.

If the chosen channel was used for a receive, the r_i component is set to the received value, where i is the index of that state among all n receive states; otherwise r_i has the zero value of type T_i. Note that the receive index i is not the same as the state index index.

The second component of the triple, recvOk, is a boolean whose value is true iff the selected operation was a receive and the receive successfully yielded a value.

Pos() returns the ast.SelectStmt.Select.

Example printed form: 

t3 = select nonblocking [<-t0, t1<-t2]
t4 = select blocking []

func (*Select) Name 

func (v *Select) Name() string

func (*Select) Operands 

func (v *Select) Operands(rands []*Value) []*Value

func (*Select) Pos 

func (v *Select) Pos() token.Pos

func (*Select) Referrers 

func (v *Select) Referrers() *[]Instruction

func (*Select) String 

func (s *Select) String() string

func (*Select) Type 

func (v *Select) Type() types.Type

type SelectState 

type SelectState struct {
	Dir       types.ChanDir // direction of case (SendOnly or RecvOnly)
	Chan      Value         // channel to use (for send or receive)
	Send      Value         // value to send (for send)
	Pos       token.Pos     // position of token.ARROW
	DebugNode ast.Node      // ast.SendStmt or ast.UnaryExpr(<-) [debug mode]
}

SelectState is a helper for Select. It represents one goal state and its corresponding communication.

type Send 

type Send struct {
	Chan, X Value
	// contains filtered or unexported fields
}

The Send instruction sends X on channel Chan.

Pos() returns the ast.SendStmt.Arrow, if explicit in the source.

Example printed form: 

send t0 <- t1

func (*Send) Block 

func (v *Send) Block() *BasicBlock

func (*Send) Operands 

func (s *Send) Operands(rands []*Value) []*Value

func (*Send) Parent 

func (v *Send) Parent() *Function

func (*Send) Pos 

func (s *Send) Pos() token.Pos

func (*Send) Referrers 

func (v *Send) Referrers() *[]Instruction

func (*Send) String 

func (s *Send) String() string

type Sigma 

type Sigma struct {
	X      Value
	Branch bool
	// contains filtered or unexported fields
}

func (*Sigma) Name 

func (v *Sigma) Name() string

func (*Sigma) Operands 

func (v *Sigma) Operands(rands []*Value) []*Value

func (*Sigma) Pos 

func (v *Sigma) Pos() token.Pos

func (*Sigma) Referrers 

func (v *Sigma) Referrers() *[]Instruction

func (*Sigma) String 

func (p *Sigma) String() string

func (*Sigma) Type 

func (v *Sigma) Type() types.Type

func (*Sigma) Value 

func (p *Sigma) Value() Value

type Slice 

type Slice struct {
	X              Value // slice, string, or *array
	Low, High, Max Value // each may be nil
	// contains filtered or unexported fields
}

The Slice instruction yields a slice of an existing string, slice or *array X between optional integer bounds Low and High.

Dynamically, this instruction panics if X evaluates to a nil *array pointer.

Type() returns string if the type of X was string, otherwise a *types.Slice with the same element type as X.

Pos() returns the ast.SliceExpr.Lbrack if created by a x[:] slice operation, the ast.CompositeLit.Lbrace if created by a literal, or NoPos if not explicit in the source (e.g. a variadic argument slice).

Example printed form: 

t1 = slice t0[1:]

func (*Slice) Name 

func (v *Slice) Name() string

func (*Slice) Operands 

func (v *Slice) Operands(rands []*Value) []*Value

func (*Slice) Pos 

func (v *Slice) Pos() token.Pos

func (*Slice) Referrers 

func (v *Slice) Referrers() *[]Instruction

func (*Slice) String 

func (v *Slice) String() string

func (*Slice) Type 

func (v *Slice) Type() types.Type

type Store 

type Store struct {
	Addr Value
	Val  Value
	// contains filtered or unexported fields
}

The Store instruction stores Val at address Addr. Stores can be of arbitrary types.

Pos() returns the position of the source-level construct most closely associated with the memory store operation. Since implicit memory stores are numerous and varied and depend upon implementation choices, the details are not specified.

Example printed form: 

*x = y

func (*Store) Block 

func (v *Store) Block() *BasicBlock

func (*Store) Operands 

func (s *Store) Operands(rands []*Value) []*Value

func (*Store) Parent 

func (v *Store) Parent() *Function

func (*Store) Pos 

func (s *Store) Pos() token.Pos

func (*Store) Referrers 

func (v *Store) Referrers() *[]Instruction

func (*Store) String 

func (s *Store) String() string

type Type 

type Type struct {
	// contains filtered or unexported fields
}

A Type is a Member of a Package representing a package-level named type.

Type() returns a *types.Named.

func (*Type) Name 

func (t *Type) Name() string

func (*Type) Object 

func (t *Type) Object() types.Object

func (*Type) Package 

func (t *Type) Package() *Package

func (*Type) Pos 

func (t *Type) Pos() token.Pos

func (*Type) RelString 

func (t *Type) RelString(from *types.Package) string

func (*Type) String 

func (t *Type) String() string

func (*Type) Token 

func (t *Type) Token() token.Token

func (*Type) Type 

func (t *Type) Type() types.Type

type TypeAssert 

type TypeAssert struct {
	X            Value
	AssertedType types.Type
	CommaOk      bool
	// contains filtered or unexported fields
}

The TypeAssert instruction tests whether interface value X has type AssertedType.

If !CommaOk, on success it returns v, the result of the conversion (defined below); on failure it panics.

If CommaOk: on success it returns a pair (v, true) where v is the result of the conversion; on failure it returns (z, false) where z is AssertedType's zero value. The components of the pair must be accessed using the Extract instruction.

If AssertedType is a concrete type, TypeAssert checks whether the dynamic type in interface X is equal to it, and if so, the result of the conversion is a copy of the value in the interface.

If AssertedType is an interface, TypeAssert checks whether the dynamic type of the interface is assignable to it, and if so, the result of the conversion is a copy of the interface value X. If AssertedType is a superinterface of X.Type(), the operation will fail iff the operand is nil. (Contrast with ChangeInterface, which performs no nil-check.)

Type() reflects the actual type of the result, possibly a 2-types.Tuple; AssertedType is the asserted type.

Pos() returns the ast.CallExpr.Lparen if the instruction arose from an explicit T(e) conversion; the ast.TypeAssertExpr.Lparen if the instruction arose from an explicit e.(T) operation; or the ast.CaseClause.Case if the instruction arose from a case of a type-switch statement.

Example printed form: 

t1 = typeassert t0.(int)
t3 = typeassert,ok t2.(T)

func (*TypeAssert) Name 

func (v *TypeAssert) Name() string

func (*TypeAssert) Operands 

func (v *TypeAssert) Operands(rands []*Value) []*Value

func (*TypeAssert) Pos 

func (v *TypeAssert) Pos() token.Pos

func (*TypeAssert) Referrers 

func (v *TypeAssert) Referrers() *[]Instruction

func (*TypeAssert) String 

func (v *TypeAssert) String() string

func (*TypeAssert) Type 

func (v *TypeAssert) Type() types.Type

type UnOp 

type UnOp struct {
	Op      token.Token // One of: NOT SUB ARROW MUL XOR ! - <- * ^
	X       Value
	CommaOk bool
	// contains filtered or unexported fields
}

The UnOp instruction yields the result of Op X. ARROW is channel receive. MUL is pointer indirection (load). XOR is bitwise complement. SUB is negation. NOT is logical negation.

If CommaOk and Op=ARROW, the result is a 2-tuple of the value above and a boolean indicating the success of the receive. The components of the tuple are accessed using Extract.

Pos() returns the ast.UnaryExpr.OpPos, if explicit in the source. For receive operations (ARROW) implicit in ranging over a channel, Pos() returns the ast.RangeStmt.For. For implicit memory loads (STAR), Pos() returns the position of the most closely associated source-level construct; the details are not specified.

Example printed form: 

t0 = *x
t2 = <-t1,ok

func (*UnOp) Name 

func (v *UnOp) Name() string

func (*UnOp) Operands 

func (v *UnOp) Operands(rands []*Value) []*Value

func (*UnOp) Pos 

func (v *UnOp) Pos() token.Pos

func (*UnOp) Referrers 

func (v *UnOp) Referrers() *[]Instruction

func (*UnOp) String 

func (v *UnOp) String() string

func (*UnOp) Type 

func (v *UnOp) Type() types.Type

type Value 

type Value interface {
	// Name returns the name of this value, and determines how
	// this Value appears when used as an operand of an
	// Instruction.
	//
	// This is the same as the source name for Parameters,
	// Builtins, Functions, FreeVars, Globals.
	// For constants, it is a representation of the constant's value
	// and type.  For all other Values this is the name of the
	// virtual register defined by the instruction.
	//
	// The name of an SSA Value is not semantically significant,
	// and may not even be unique within a function.
	Name() string

	// If this value is an Instruction, String returns its
	// disassembled form; otherwise it returns unspecified
	// human-readable information about the Value, such as its
	// kind, name and type.
	String() string

	// Type returns the type of this value.  Many instructions
	// (e.g. IndexAddr) change their behaviour depending on the
	// types of their operands.
	Type() types.Type

	// Parent returns the function to which this Value belongs.
	// It returns nil for named Functions, Builtin, Const and Global.
	Parent() *Function

	// Referrers returns the list of instructions that have this
	// value as one of their operands; it may contain duplicates
	// if an instruction has a repeated operand.
	//
	// Referrers actually returns a pointer through which the
	// caller may perform mutations to the object's state.
	//
	// Referrers is currently only defined if Parent()!=nil,
	// i.e. for the function-local values FreeVar, Parameter,
	// Functions (iff anonymous) and all value-defining instructions.
	// It returns nil for named Functions, Builtin, Const and Global.
	//
	// Instruction.Operands contains the inverse of this relation.
	Referrers() *[]Instruction

	// Pos returns the location of the AST token most closely
	// associated with the operation that gave rise to this value,
	// or token.NoPos if it was not explicit in the source.
	//
	// For each ast.Node type, a particular token is designated as
	// the closest location for the expression, e.g. the Lparen
	// for an *ast.CallExpr.  This permits a compact but
	// approximate mapping from Values to source positions for use
	// in diagnostic messages, for example.
	//
	// (Do not use this position to determine which Value
	// corresponds to an ast.Expr; use Function.ValueForExpr
	// instead.  NB: it requires that the function was built with
	// debug information.)
	Pos() token.Pos
}

A Value is an SSA value that can be referenced by an instruction.

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