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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssa
// This package defines a high-level intermediate representation for
// Go programs using static single-assignment (SSA) form.
import (
"fmt"
"go/ast"
exact "go/constant"
"go/token"
"go/types"
"sync"
"golang.org/x/tools/go/types/typeutil"
)
// A Program is a partial or complete Go program converted to SSA form.
type Program struct {
Fset *token.FileSet // position information for the files of this Program
imported map[string]*Package // all importable Packages, keyed by import path
packages map[*types.Package]*Package // all loaded Packages, keyed by object
mode BuilderMode // set of mode bits for SSA construction
MethodSets typeutil.MethodSetCache // cache of type-checker's method-sets
methodsMu sync.Mutex // guards the following maps:
methodSets typeutil.Map // maps type to its concrete methodSet
runtimeTypes typeutil.Map // types for which rtypes are needed
canon typeutil.Map // type canonicalization map
bounds map[*types.Func]*Function // bounds for curried x.Method closures
thunks map[selectionKey]*Function // thunks for T.Method expressions
}
// 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.
//
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)
values map[types.Object]Value // package members (incl. types and methods), keyed by object
init *Function // Func("init"); the package's init function
debug bool // include full debug info in this package
// The following fields are set transiently, then cleared
// after building.
buildOnce sync.Once // ensures package building occurs once
ninit int32 // number of init functions
info *types.Info // package type information
files []*ast.File // package ASTs
}
// 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 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 Type is a Member of a Package representing a package-level named type.
type Type struct {
object *types.TypeName
pkg *Package
}
// 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.
//
type NamedConst struct {
object *types.Const
Value *Const
pkg *Package
}
// A Value is an SSA value that can be referenced by an instruction.
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
}
// 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.
//
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
// setBlock sets the basic block to which this instruction belongs.
setBlock(*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
}
// 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 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
}
// 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.
//
type Function struct {
name string
object types.Object // a declared *types.Func or one of its wrappers
method *types.Selection // info about provenance of synthetic methods
Signature *types.Signature
pos token.Pos
Synthetic string // provenance of synthetic function; "" for true source functions
syntax ast.Node // *ast.Func{Decl,Lit}; replaced with simple ast.Node after build, unless debug mode
parent *Function // enclosing function if anon; nil if global
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
referrers []Instruction // referring instructions (iff Parent() != nil)
// The following fields are set transiently during building,
// then cleared.
currentBlock *BasicBlock // where to emit code
objects map[types.Object]Value // addresses of local variables
namedResults []*Alloc // tuple of named results
targets *targets // linked stack of branch targets
lblocks map[*ast.Object]*lblock // labelled blocks
}
// 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).
//
type BasicBlock struct {
Index int // index of this block within Parent().Blocks
Comment string // optional label; no semantic significance
parent *Function // parent function
Instrs []Instruction // instructions in order
Preds, Succs []*BasicBlock // predecessors and successors
succs2 [2]*BasicBlock // initial space for Succs
dom domInfo // dominator tree info
gaps int // number of nil Instrs (transient)
rundefers int // number of rundefers (transient)
}
// Pure values ----------------------------------------
// 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.
//
type FreeVar struct {
name string
typ types.Type
pos token.Pos
parent *Function
referrers []Instruction
// Transiently needed during building.
outer Value // the Value captured from the enclosing context.
}
// A Parameter represents an input parameter of a function.
//
type Parameter struct {
name string
object types.Object // a *types.Var; nil for non-source locals
typ types.Type
pos token.Pos
parent *Function
referrers []Instruction
}
// 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
//
type Const struct {
typ types.Type
Value exact.Value
}
// A Global is a named Value holding the address of a package-level
// variable.
//
// Pos() returns the position of the ast.ValueSpec.Names[*]
// identifier.
//
type Global struct {
name string
object types.Object // a *types.Var; may be nil for synthetics e.g. init$guard
typ types.Type
pos token.Pos
Pkg *Package
}
// 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.
//
type Builtin struct {
name string
sig *types.Signature
}
// Value-defining instructions ----------------------------------------
// 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
//
type Alloc struct {
register
Comment string
Heap bool
index int // dense numbering; for lifting
}
var _ Instruction = (*Sigma)(nil)
var _ Value = (*Sigma)(nil)
type Sigma struct {
register
X Value
Branch bool
}
func (p *Sigma) Value() Value {
v := p.X
for {
sigma, ok := v.(*Sigma)
if !ok {
break
}
v = sigma
}
return v
}
func (p *Sigma) String() string {
return fmt.Sprintf("σ [%s.%t]", relName(p.X, p), p.Branch)
}
// 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]
//
type Phi struct {
register
Comment string // a hint as to its purpose
Edges []Value // Edges[i] is value for Block().Preds[i]
}
// 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)
//
type Call struct {
register
Call CallCommon
}
// 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
//
type BinOp struct {
register
// 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
}
// 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
//
type UnOp struct {
register
Op token.Token // One of: NOT SUB ARROW MUL XOR ! - <- * ^
X Value
CommaOk bool
}
// 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)
//
type ChangeType struct {
register
X Value
}
// 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.
10BC8
// - 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)
//
type Convert struct {
register
X Value
}
// 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)
//
type ChangeInterface struct {
register
X Value
}
// 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
//
type MakeInterface struct {
register
X Value
}
// 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]
//
type MakeClosure struct {
register
Fn Value // always a *Function
Bindings []Value // values for each free variable in Fn.FreeVars
}
// 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
//
type MakeMap struct {
register
Reserve Value // initial space reservation; nil => default
}
// 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
//
type MakeChan struct {
register
Size Value // int; size of buffer; zero => synchronous.
}
// 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
//
type MakeSlice struct {
register
Len Value
Cap Value
}
// 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:]
//
type Slice struct {
register
X Value // slice, string, or *array
Low, High, Max Value // each may be nil
}
// 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]
//
type FieldAddr struct {
register
X Value // *struct
Field int // index into X.Type().Deref().(*types.Struct).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]
//
type Field struct {
register
X Value // struct
Field int // index into X.Type().(*types.Struct).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]
//
type IndexAddr struct {
register
X Value // slice or *array,
Index Value // numeric index
}
// 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]
//
type Index struct {
register
X Value // array
Index Value // integer index
}
// 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
//
type Lookup struct {
register
X Value // string or map
Index Value // numeric or key-typed index
CommaOk bool // return a value,ok pair
}
// SelectState is a helper for Select.
// It represents one goal state and its corresponding communication.
//
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]
}
// 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 []
//
type Select struct {
register
States []*SelectState
Blocking bool
}
// 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
//
type Range struct {
register
X Value // string or map
}
// 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
//
type Next struct {
register
Iter Value
IsString bool // true => string iterator; false => map iterator.
}
// 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
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