// 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 ir

// This package defines a high-level intermediate representation for
// Go programs using static single-information (SSI) form.

import (
	"fmt"
	"go/ast"
	"go/constant"
	"go/token"
	"go/types"
	"math/big"
	"sync"

	"honnef.co/go/tools/go/types/typeutil"
)

const (
	// Replace CompositeValue with only constant values with AggregateConst. Currently disabled because it breaks field
	// tracking in U1000.
	doSimplifyConstantCompositeValues = false
)

type ID int

// A Program is a partial or complete Go program converted to IR form.
type Program struct {
	Fset       *token.FileSet              // position information for the files of this Program
	PrintFunc  string                      // create ir.html for function specified in PrintFunc
	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 IR construction
	MethodSets typeutil.MethodSetCache     // cache of type-checker's method-sets

	methodsMu    sync.Mutex               // guards the following maps:
	methodSets   typeutil.Map[*methodSet] // maps type to its concrete methodSet
	runtimeTypes typeutil.Map[bool]       // types for which rtypes are needed
	canon        typeutil.Map[types.Type] // type canonicalization map

	noReturn func(*types.Func) bool
}

// 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)
	Functions []*Function            // all functions, excluding anonymous ones
	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
	printFunc string                 // which function to print in HTML form

	// 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
	initVersion map[ast.Expr]string // goversion to use for each global var init expr
}

// 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
	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 IR value that can be referenced by an instruction.
type Value interface {
	setID(ID)

	// 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 IR Value is not semantically significant,
	// and may not even be unique within a function.
	Name() string

	// ID returns the ID of this value. IDs are unique within a single
	// function and are densely numbered, but may contain gaps.
	// Values and other Instructions share the same ID space.
	// Globally, values are identified by their addresses. However,
	// IDs exist to facilitate efficient storage of mappings between
	// values and data when analysing functions.
	//
	// NB: IDs are allocated late in the IR construction process and
	// are not available to early stages of said process.
	ID() ID

	// 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 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 and Global.
	//
	// Instruction.Operands contains the inverse of this relation.
	Referrers() *[]Instruction

	Operands(rands []*Value) []*Value // nil for non-Instructions

	// Source returns the AST node responsible for creating this
	// value. A single AST node may be responsible for more than one
	// value, and not all values have an associated AST node.
	//
	// Do not use this method to find a Value given an ast.Expr; use
	// ValueForExpr instead.
	Source() ast.Node

	// Pos returns Source().Pos() if Source is not nil, else it
	// returns token.NoPos.
	Pos() token.Pos
}

// An Instruction is an IR 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 {
	setSource(ast.Node)
	setID(ID)

	Comment() string

	// String returns the disassembled form of this value.
	//
	// Examples of Instructions that are Values:
	//       "BinOp <int> {+} t1 t2"  (BinOp)
	//       "Call <int> len t1"      (Call)
	// Note that the name of the Value is not printed.
	//
	// Examples of Instructions that are not Values:
	//       "Return t1"              (Return)
	//       "Store {int} t2 t1"      (Store)
	//
	// (The separation of 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

	// ID returns the ID of this instruction. IDs are unique within a single
	// function and are densely numbered, but may contain gaps.
	// Globally, instructions are identified by their addresses. However,
	// IDs exist to facilitate efficient storage of mappings between
	// instructions and data when analysing functions.
	//
	// NB: IDs are allocated late in the IR construction process and
	// are not available to early stages of said process.
	ID() ID

	// 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

	Referrers() *[]Instruction // nil for non-Values

	// Source returns the AST node responsible for creating this
	// instruction. A single AST node may be responsible for more than
	// one instruction, and not all instructions have an associated
	// AST node.
	Source() ast.Node

	// Pos returns Source().Pos() if Source is not nil, else it
	// returns token.NoPos.
	Pos() token.Pos
}

// A Node is a node in the IR 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 IR graph algorithms.  Clients should
// use the more specific and informative Value or Instruction
// interfaces where appropriate.
type Node interface {
	setID(ID)

	// Common methods:
	ID() ID
	String() string
	Source() ast.Node
	Pos() token.Pos
	Parent() *Function

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

type Synthetic int

const (
	SyntheticLoadedFromExportData Synthetic = iota + 1
	SyntheticPackageInitializer
	SyntheticThunk
	SyntheticWrapper
	SyntheticBound
	SyntheticGeneric
	SyntheticRangeOverFuncYield
)

func (syn Synthetic) String() string {
	switch syn {
	case SyntheticLoadedFromExportData:
		return "loaded from export data"
	case SyntheticPackageInitializer:
		return "package initializer"
	case SyntheticThunk:
		return "thunk"
	case SyntheticWrapper:
		return "wrapper"
	case SyntheticBound:
		return "bound"
	case SyntheticGeneric:
		return "generic"
	case SyntheticRangeOverFuncYield:
		return "range-over-func yield"
	default:
		return fmt.Sprintf("Synthetic(%d)", syn)
	}
}

// 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, Locals, and
// Params 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().
//
// 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.
//
// When the operand of a range statement is an iterator function,
// the loop body is transformed into a synthetic anonymous function
// that is passed as the yield argument in a call to the iterator.
// In that case, Function.Source() is the ast.RangeStmt.
//
// Synthetic functions, for which Synthetic != "", are functions
// that do not appear in the source AST. These include:
//   - method wrappers,
//   - thunks,
//   - bound functions,
//   - empty functions built from loaded type information,
//   - yield functions created from range-over-func loops, and
//   - package init functions.
//
// Type() returns the function's Signature.
type Function struct {
	node

	name      string
	object    *types.Func      // symbol for declared function (nil for FuncLit or synthetic init)
	method    *types.Selection // info about provenance of synthetic methods
	Signature *types.Signature
	generics  instanceWrapperMap

	Synthetic Synthetic // provenance of synthetic function; 0 for true source functions
	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

	// These fields are populated only when the function body is built:

	Params    []*Parameter  // function parameters; for methods, includes receiver
	FreeVars  []*FreeVar    // free variables whose values must be supplied by closure
	Locals    []*Alloc      // frame-allocated variables of this function
	Blocks    []*BasicBlock // basic blocks of the function; nil => external
	Exit      *BasicBlock   // The function's exit block
	AnonFuncs []*Function   // anonymous functions (from FuncLit, RangeStmt) directly beneath this one
	referrers []Instruction // referring instructions (iff Parent() != nil)

	goversion string // Go version of syntax (NB: init is special)

	// uniq is not stored in functionBody because we need it after function building finishes
	uniq int64 // source of unique ints within the source tree while building

	*functionBody
}

type instanceWrapperMap struct {
	h       typeutil.Hasher
	entries map[uint32][]struct {
		key *types.TypeList
		val *Function
	}
	len int
}

func typeListIdentical(l1, l2 *types.TypeList) bool {
	if l1.Len() != l2.Len() {
		return false
	}
	for i := 0; i < l1.Len(); i++ {
		t1 := l1.At(i)
		t2 := l2.At(i)
		if !types.Identical(t1, t2) {
			return false
		}
	}
	return true
}

func (m *instanceWrapperMap) At(key *types.TypeList) *Function {
	if m.entries == nil {
		m.entries = make(map[uint32][]struct {
			key *types.TypeList
			val *Function
		})
		m.h = typeutil.MakeHasher()
	}

	var hash uint32
	for t := range key.Types() {
		hash += m.h.Hash(t)
	}

	for _, e := range m.entries[hash] {
		if typeListIdentical(e.key, key) {
			return e.val
		}
	}
	return nil
}

func (m *instanceWrapperMap) Set(key *types.TypeList, val *Function) {
	if m.entries == nil {
		m.entries = make(map[uint32][]struct {
			key *types.TypeList
			val *Function
		})
		m.h = typeutil.MakeHasher()
	}

	var hash uint32
	for t := range key.Types() {
		hash += m.h.Hash(t)
	}
	for i, e := range m.entries[hash] {
		if typeListIdentical(e.key, key) {
			m.entries[hash][i].val = val
			return
		}
	}
	m.entries[hash] = append(m.entries[hash], struct {
		key *types.TypeList
		val *Function
	}{key, val})
	m.len++
}

func (m *instanceWrapperMap) Len() int {
	return m.len
}

type constValue struct {
	c   Constant
	idx int
}

type functionBody struct {
	// The following fields are set transiently during building,
	// then cleared.
	currentBlock *BasicBlock              // where to emit code
	vars         map[*types.Var]Value     // addresses of local variables
	results      []*Alloc                 // result allocations of the current function
	returnVars   []*types.Var             // variables for a return statement. Either results or for range-over-func a parent's results
	targets      *targets                 // linked stack of branch targets
	lblocks      map[*types.Label]*lblock // labelled blocks
	jump         *types.Var               // synthetic variable for the yield state (non-nil => range-over-func)
	deferstack   *types.Var               // synthetic variable holding enclosing ssa:deferstack()
	sourceFn     *Function                // nearest enclosing source function
	exits        []*exit                  // exits of the function that need to be resolved

	consts          map[constKey]constValue
	aggregateConsts typeutil.Map[[]*AggregateConst]

	wr        *HTMLWriter
	fakeExits BlockSet
	blocksets [5]BlockSet
	hasDefer  bool

	// a contiguous block of instructions that will be used by blocks,
	// to avoid making multiple allocations.
	scratchInstructions []Instruction
}

// BasicBlock represents an IR basic block.
//
// The final element of Instrs is always an explicit transfer of
// control (If, Jump, Return, Panic, or Unreachable).
//
// 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 IR 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
	pdom         domInfo        // post-dominator tree info
	post         int
	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 {
	node

	name      string
	typ       types.Type
	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 {
	register

	name   string
	object *types.Var // non-nil
}

// 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/constant uses for
// constants, or nil for a typed nil value.
//
// Pos() returns token.NoPos.
//
// Example printed form:
//
//	Const <int> {42}
//	Const <untyped string> {"test"}
//	Const <MyComplex> {(3 + 4i)}
type Const struct {
	register

	Value constant.Value
}

type AggregateConst struct {
	register

	Values []Value
}

type CompositeValue struct {
	register

	// Bitmap records which elements were explicitly provided. For example, [4]byte{2: x} would have a bitmap of 0010.
	Bitmap big.Int
	// The number of bits set in Bitmap
	NumSet int
	// Dense list of values in the composite literal. Omitted elements are filled in with zero values.
	Values []Value
}

// TODO add the element's zero constant to ArrayConst
type ArrayConst struct {
	register
}

type GenericConst struct {
	register
}

type Constant interface {
	Instruction
	Value
	aConstant()
	RelString(*types.Package) string
	equal(Constant) bool
	setType(types.Type)
}

func (*Const) aConstant()          {}
func (*AggregateConst) aConstant() {}
func (*ArrayConst) aConstant()     {}
func (*GenericConst) aConstant()   {}

// 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 {
	node

	name   string
	object types.Object // a *types.Var; may be nil for synthetics e.g. init$guard
	typ    types.Type

	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 ir-defined
// intrinsics:
//
//	// wrapnilchk returns ptr if non-nil, panics otherwise.
//	// (For use in indirection wrappers.)
//	func ir:wrapnilchk(ptr *T, recvType, methodName string) *T
//
//	// noreturnWasPanic returns true if the previously called
//	// function panicked, false if it exited the process.
//	func ir:noreturnWasPanic() bool
//
// 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 {
	node

	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 zero-initializes the same local variable in
// the call frame and returns its address; in this case the Alloc must
// be present in Function.Locals. We call this a "local" alloc.
//
// If Heap is true, Alloc allocates a new zero-initialized variable
// each time the instruction is executed. We call this a "new" alloc.
//
// 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:
//
//	t1 = StackAlloc <*int>
//	t2 = HeapAlloc <*int> (new)
type Alloc struct {
	register
	Heap  bool
	index int // dense numbering; for lifting
}

var _ Instruction = (*Sigma)(nil)
var _ Value = (*Sigma)(nil)

// The Sigma instruction represents an SSI σ-node, which splits values
// at branches in the control flow.
//
// Conceptually, σ-nodes exist at the end of blocks that branch and
// constitute parallel assignments to one value per destination block.
// However, such a representation would be awkward to work with, so
// instead we place σ-nodes at the beginning of branch targets. The
// From field denotes to which incoming edge the node applies.
//
// Within a block, all σ-nodes must appear before all non-σ nodes.
//
// Example printed form:
//
//	t2 = Sigma <int> [#0] t1 (x)
type Sigma struct {
	register
	From *BasicBlock
	X    Value

	live bool // used during lifting
}

type CopyInfo uint64

const (
	CopyInfoUnspecified CopyInfo = 0
	CopyInfoNotNil      CopyInfo = 1 << iota
	CopyInfoNotZeroLength
	CopyInfoNotNegative
	CopyInfoSingleConcreteType
	CopyInfoClosed
)

type Copy struct {
	register
	X    Value
	Why  Instruction
	Info CopyInfo
}

// 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, non-σ
// 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:
//
//	t3 = Phi <int> 2:t1 4:t2 (x)
type Phi struct {
	register
	Edges []Value // Edges[i] is value for Block().Preds[i]

	live bool // used during lifting
}

// 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:
//
//	t3 = Call <()> println t1 t2
//	t4 = Call <()> foo$1
//	t6 = Invoke <string> t5.String
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:
//
//	t3 = BinOp <int> {+} t2 t1
type BinOp struct {
	register
	// One of:
	// ADD SUB MUL QUO REM          + - * / %
	// AND OR XOR SHL SHR AND_NOT   & | ^ << >> &^
	// EQL NEQ LSS LEQ GTR GEQ      == != < <= < >=
	Op   token.Token
	X, Y Value
}

// The UnOp instruction yields the result of Op X.
// XOR is bitwise complement.
// SUB is negation.
// NOT is logical negation.
//
// Example printed form:
//
//	t2 = UnOp <int> {^} t1
type UnOp struct {
	register
	Op token.Token // One of: NOT SUB XOR ! - ^
	X  Value
}

// The Load instruction loads a value from a memory address.
//
// For implicit memory loads, Pos() returns the position of the
// most closely associated source-level construct; the details are not
// specified.
//
// Example printed form:
//
//	t2 = Load <int> t1
type Load struct {
	register
	X Value
}

// 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:
//
//	t2 = ChangeType <*T> t1
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.
//   - 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 IR construction.
//
// Pos() returns the ast.CallExpr.Lparen, if the instruction arose
// from an explicit conversion in the source.
//
// Example printed form:
//
//	t2 = Convert <[]byte> t1
type Convert struct {
	register
	X Value
}

// The MultiConvert instruction yields the conversion of value X to type
// Type(). Either X.Type() or Type() must be a type parameter. Each
// type in the type set of X.Type() can be converted to each type in the
// type set of Type().
//
// See the documentation for Convert, ChangeType, SliceToArray, and SliceToArrayPointer
// for the conversions that are permitted.
//
// This operation can fail dynamically (see SliceToArrayPointer).
//
// Example printed form:
//
//	t1 = multiconvert D <- S (t0) [*[2]rune <- []rune | string <- []rune]
type MultiConvert struct {
	register
	X    Value
	from typeutil.TypeSet
	to   typeutil.TypeSet
}

// 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:
//
//	t2 = ChangeInterface <I1> t1
type ChangeInterface struct {
	register
	X Value
}

// The SliceToArrayPointer instruction yields the conversion of slice X to
// array pointer.
//
// Pos() returns the ast.CallExpr.Lparen, if the instruction arose
// from an explicit conversion in the source.
//
// Example printed form:
//
//	t2 = SliceToArrayPointer <*[4]byte> t1
type SliceToArrayPointer struct {
	register
	X Value
}

// The SliceToArray instruction yields the conversion of slice X to
// array.
//
// Pos() returns the ast.CallExpr.Lparen, if the instruction arose
// from an explicit conversion in the source.
//
// Example printed form:
//
//	t2 = SliceToArray <[4]byte> t1
type SliceToArray 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.MethodValue(m) to find the implementation of a method.
//
// To construct the zero value of an interface type T, use:
//
//	NewConst(constant.MakeNil(), T, pos)
//
// Pos() returns the ast.CallExpr.Lparen, if the instruction arose
// from an explicit conversion in the source.
//
// Example printed form:
//
//	t2 = MakeInterface <interface{}> t1
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:
//
//	t1 = MakeClosure <func()> foo$1 t1 t2
//	t5 = MakeClosure <func(int)> (T).foo$bound t4
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 = MakeMap <map[string]int>
//	t2 = MakeMap <StringIntMap> t1
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:
//
//	t3 = MakeChan <chan int> t1
//	t4 = MakeChan <chan IntChan> t2
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:
//
//	t3 = MakeSlice <[]string> t1 t2
//	t4 = MakeSlice <StringSlice> t1 t2
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:
//
//	t4 = Slice <[]int> t3 t2 t1 <nil>
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:
//
//	t2 = FieldAddr <*int> [0] (X) t1
type FieldAddr struct {
	register
	X     Value // *struct
	Field int   // field is X.Type().Underlying().(*types.Pointer).Elem().Underlying().(*types.Struct).Field(Field)
}

// 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:
//
//	t2 = FieldAddr <int> [0] (X) t1
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 StringLookup, MapLookup 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:
//
//	t3 = IndexAddr <*int> t2 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:
//
//	t3 = Index <int> t2 t1
type Index struct {
	register
	X     Value // array
	Index Value // integer index
}

// The MapLookup instruction yields element Index of collection X, 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:
//
//	t4 = MapLookup <string> t3 t1
//	t6 = MapLookup <(string, bool)> t3 t2
type MapLookup struct {
	register
	X       Value // map
	Index   Value // key-typed index
	CommaOk bool  // return a value,ok pair
}

// The StringLookup instruction yields element Index of collection X, a string.
// Index is an integer expression.
//
// Pos() returns the ast.IndexExpr.Lbrack, if explicit in the source.
//
// Example printed form:
//
//	t3 = StringLookup <uint8> t2 t1
type StringLookup struct {
	register
	X     Value // string
	Index Value // numeric index
}

// 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 Tᵢ (0 ≤ i < n)
// be the element type of each such state's Chan.
// Select returns an n+2-tuple
//
//	(index int, recvOk bool, r₀ T₀, ... rₙ-1 Tₙ-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 rᵢ component is
// set to the received value, where i is the index of that state among
// all n receive states; otherwise rᵢ has the zero value of type Tᵢ.
// 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:
//
//	t6 = SelectNonBlocking <(index int, ok bool, int)> [<-t4, t5<-t1]
//	t11 = SelectBlocking <(index int, ok bool)> []
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:
//
//	t2 = Range <iter> t1
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:
//
//	t5 = Next <(ok bool, k int, v rune)> t2
//	t5 = Next <(ok bool, k invalid type, v invalid type)> t2
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
// 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:
//
//	t2 = TypeAssert <int> t1
//	t4 = TypeAssert <(value fmt.Stringer, ok bool)> t1
type TypeAssert struct {
	register
	X            Value
	AssertedType types.Type
	CommaOk      bool
}

// 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, Recv,
// MapLookup and others.
//
// Example printed form:
//
//	t7 = Extract <bool> [1] (ok) t4
type Extract struct {
	register
	Tuple Value
	Index int
}

// Instructions executed for effect.  They do not yield a value. --------------------

// 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 → b1
type Jump struct {
	anInstruction
}

// The Unreachable pseudo-instruction signals that execution cannot
// continue after the preceding function call because it terminates
// the process.
//
// The instruction acts as a control instruction, jumping to the exit
// block. However, this jump will never execute.
//
// An Unreachable instruction must be the last instruction of its
// containing BasicBlock.
//
// Example printed form:
//
//	Unreachable → b1
type Unreachable struct {
	anInstruction
}

// 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 the *ast.IfStmt, if explicit in the source.
//
// Example printed form:
//
//	If t2 → b1 b2
type If struct {
	anInstruction
	Cond Value
}

type ConstantSwitch struct {
	anInstruction
	Tag Value
	// Constant branch conditions. A nil Value denotes the (implicit
	// or explicit) default branch.
	Conds []Value
}

type TypeSwitch struct {
	register
	Tag   Value
	Conds []types.Type
}

// 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, MapLookup or Recv 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 t1 t2
type Return struct {
	anInstruction
	Results []Value
}

// 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
type RunDefers struct {
	anInstruction
}

// The Panic instruction initiates a panic with value X.
//
// A Panic instruction must be the last instruction of its containing
// BasicBlock, which must have one successor, the exit block.
//
// 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 t1
type Panic struct {
	anInstruction
	X Value // an interface{}
}

// 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 t1
//	Go t3
//	GoInvoke t4.Bar t2
type Go struct {
	anInstruction
	Call CallCommon
}

// The Defer instruction pushes the specified call onto a stack of
// functions to be called by a RunDefers instruction or by a panic.
//
// If _DeferStack != nil, it indicates the defer list that the defer is
// added to. Defer list values come from the Builtin function
// ssa:deferstack. Calls to ssa:deferstack() produces the defer stack
// of the current function frame. _DeferStack allows for deferring into an
// alternative function stack than the current function.
//
// See CallCommon for generic function call documentation.
//
// Pos() returns the ast.DeferStmt.Defer.
//
// Example printed form:
//
//	Defer println t1
//	Defer t3
//	DeferInvoke t4.Bar t2
type Defer struct {
	anInstruction
	Call        CallCommon
	_DeferStack Value // stack (from ssa:deferstack() intrinsic) onto which this function is pushed

	// TODO: Exporting _DeferStack and possibly making _DeferStack != nil awaits proposal https://github.com/golang/go/issues/66601.
}

// The Send instruction sends X on channel Chan.
//
// Pos() returns the ast.SendStmt.Arrow, if explicit in the source.
//
// Example printed form:
//
//	Send t2 t1
type Send struct {
	anInstruction
	Chan, X Value
}

// The Recv instruction receives from channel Chan.
//
// If CommaOk, 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 implicit in ranging over a channel,
// Pos() returns the ast.RangeStmt.For.
//
// Example printed form:
//
//	t2 = Recv <int> t1
//	t3 = Recv <(int, bool)> t1
type Recv struct {
	register
	Chan    Value
	CommaOk bool
}

// 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:
//
//	Store {int} t2 t1
type Store struct {
	anInstruction
	Addr Value
	Val  Value
}

// 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:
//
//	BlankStore t1
type BlankStore struct {
	anInstruction
	Val Value
}

// 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:
//
//	MapUpdate t3 t1 t2
type MapUpdate struct {
	anInstruction
	Map   Value
	Key   Value
	Value Value
}

// A DebugRef instruction maps a source-level expression Expr to the
// IR 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.
//
// 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
type DebugRef struct {
	anInstruction
	Expr   ast.Expr     // the referring expression (never *ast.ParenExpr)
	object types.Object // the identity of the source var/func
	IsAddr bool         // Expr is addressable and X is the address it denotes
	X      Value        // the value or address of Expr
}

// Embeddable mix-ins and helpers for common parts of other structs. -----------

// register is a mix-in embedded by all IR values that are also
// instructions, i.e. virtual registers, and provides a uniform
// implementation of most of the Value interface: Value.Name() is a
// numbered register (e.g. "t0"); the other methods are field accessors.
//
// Temporary names are automatically assigned to each register on
// completion of building a function in IR form.
type register struct {
	anInstruction
	typ       types.Type // type of virtual register
	referrers []Instruction
}

type node struct {
	source ast.Node
	id     ID
}

func (n *node) setID(id ID) { n.id = id }
func (n node) ID() ID       { return n.id }

func (n *node) setSource(source ast.Node) { n.source = source }
func (n *node) Source() ast.Node          { return n.source }

func (n *node) Pos() token.Pos {
	if n.source != nil {
		return n.source.Pos()
	}
	return token.NoPos
}

// anInstruction is a mix-in embedded by all Instructions.
// It provides the implementations of the Block and setBlock methods.
type anInstruction struct {
	node
	block   *BasicBlock // the basic block of this instruction
	comment string
}

func (instr anInstruction) Comment() string {
	return instr.comment
}

// 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:
//
//	t3 = Call <()> println t1 t2
//	Go t3
//	Defer t3
//
// 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:
//
//	t6 = Invoke <string> t5.String
//	GoInvoke t4.Bar t2
//	DeferInvoke t4.Bar t2
//
// For all calls to variadic functions (Signature().Variadic()),
// the last element of Args is a slice.
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)
	TypeArgs []types.Type
	Results  Value
}

// IsInvoke returns true if this call has "invoke" (not "call") mode.
func (c *CallCommon) IsInvoke() bool {
	return c.Method != nil
}

// 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 (c *CallCommon) Signature() *types.Signature {
	if c.Method != nil {
		return c.Method.Type().(*types.Signature)
	}
	return typeutil.CoreType(c.Value.Type()).(*types.Signature)
}

// StaticCallee returns the callee if this is a trivially static
// "call"-mode call to a function.
func (c *CallCommon) StaticCallee() *Function {
	switch fn := c.Value.(type) {
	case *Function:
		return fn
	case *MakeClosure:
		return fn.Fn.(*Function)
	}
	return nil
}

// Description returns a description of the mode of this call suitable
// for a user interface, e.g., "static method call".
func (c *CallCommon) Description() string {
	switch fn := c.Value.(type) {
	case *Builtin:
		return "built-in function call"
	case *MakeClosure:
		return "static function closure call"
	case *Function:
		if fn.Signature.Recv() != nil {
			return "static method call"
		}
		return "static function call"
	}
	if c.IsInvoke() {
		return "dynamic method call" // ("invoke" mode)
	}
	return "dynamic function call"
}

// 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 CallInstruction interface {
	Instruction
	Common() *CallCommon // returns the common parts of the call
	Value() *Call
}

func (s *Call) Common() *CallCommon  { return &s.Call }
func (s *Defer) Common() *CallCommon { return &s.Call }
func (s *Go) Common() *CallCommon    { return &s.Call }

func (s *Call) Value() *Call  { return s }
func (s *Defer) Value() *Call { return nil }
func (s *Go) Value() *Call    { return nil }

func (v *Builtin) Type() types.Type        { return v.sig }
func (v *Builtin) Name() string            { return v.name }
func (*Builtin) Referrers() *[]Instruction { return nil }
func (v *Builtin) Pos() token.Pos          { return token.NoPos }
func (v *Builtin) Object() types.Object    { return types.Universe.Lookup(v.name) }
func (v *Builtin) Parent() *Function       { return nil }

func (v *FreeVar) Type() types.Type          { return v.typ }
func (v *FreeVar) Name() string              { return v.name }
func (v *FreeVar) Referrers() *[]Instruction { return &v.referrers }
func (v *FreeVar) Parent() *Function         { return v.parent }

func (v *Global) Type() types.Type                     { return v.typ }
func (v *Global) Name() string                         { return v.name }
func (v *Global) Parent() *Function                    { return nil }
func (v *Global) Referrers() *[]Instruction            { return nil }
func (v *Global) Token() token.Token                   { return token.VAR }
func (v *Global) Object() types.Object                 { return v.object }
func (v *Global) String() string                       { return v.RelString(nil) }
func (v *Global) Package() *Package                    { return v.Pkg }
func (v *Global) RelString(from *types.Package) string { return relString(v, from) }

func (v *Function) Name() string       { return v.name }
func (v *Function) Type() types.Type   { return v.Signature }
func (v *Function) Token() token.Token { return token.FUNC }
func (v *Function) Object() types.Object {
	if v.object != nil {
		return types.Object(v.object)
	}
	return nil
}
func (v *Function) String() string    { return v.RelString(nil) }
func (v *Function) Package() *Package { return v.Pkg }
func (v *Function) Parent() *Function { return v.parent }
func (v *Function) Referrers() *[]Instruction {
	if v.parent != nil {
		return &v.referrers
	}
	return nil
}

func (v *Parameter) Object() types.Object { return v.object }

func (v *Alloc) Type() types.Type          { return v.typ }
func (v *Alloc) Referrers() *[]Instruction { return &v.referrers }

func (v *register) Type() types.Type          { return v.typ }
func (v *register) setType(typ types.Type)    { v.typ = typ }
func (v *register) Name() string              { return fmt.Sprintf("t%d", v.id) }
func (v *register) Referrers() *[]Instruction { return &v.referrers }

func (v *anInstruction) Parent() *Function          { return v.block.parent }
func (v *anInstruction) Block() *BasicBlock         { return v.block }
func (v *anInstruction) setBlock(block *BasicBlock) { v.block = block }
func (v *anInstruction) Referrers() *[]Instruction  { return nil }

func (t *Type) Name() string                         { return t.object.Name() }
func (t *Type) Pos() token.Pos                       { return t.object.Pos() }
func (t *Type) Type() types.Type                     { return t.object.Type() }
func (t *Type) Token() token.Token                   { return token.TYPE }
func (t *Type) Object() types.Object                 { return t.object }
func (t *Type) String() string                       { return t.RelString(nil) }
func (t *Type) Package() *Package                    { return t.pkg }
func (t *Type) RelString(from *types.Package) string { return relString(t, from) }

func (c *NamedConst) Name() string                         { return c.object.Name() }
func (c *NamedConst) Pos() token.Pos                       { return c.object.Pos() }
func (c *NamedConst) String() string                       { return c.RelString(nil) }
func (c *NamedConst) Type() types.Type                     { return c.object.Type() }
func (c *NamedConst) Token() token.Token                   { return token.CONST }
func (c *NamedConst) Object() types.Object                 { return c.object }
func (c *NamedConst) Package() *Package                    { return c.pkg }
func (c *NamedConst) RelString(from *types.Package) string { return relString(c, from) }

// Func returns the package-level function of the specified name,
// or nil if not found.
func (p *Package) Func(name string) (f *Function) {
	f, _ = p.Members[name].(*Function)
	return
}

// Var returns the package-level variable of the specified name,
// or nil if not found.
func (p *Package) Var(name string) (g *Global) {
	g, _ = p.Members[name].(*Global)
	return
}

// Const returns the package-level constant of the specified name,
// or nil if not found.
func (p *Package) Const(name string) (c *NamedConst) {
	c, _ = p.Members[name].(*NamedConst)
	return
}

// Type returns the package-level type of the specified name,
// or nil if not found.
func (p *Package) Type(name string) (t *Type) {
	t, _ = p.Members[name].(*Type)
	return
}

func (s *DebugRef) Pos() token.Pos { return s.Expr.Pos() }

// Operands.

func (v *Alloc) Operands(rands []*Value) []*Value {
	return rands
}

func (v *BinOp) Operands(rands []*Value) []*Value {
	return append(rands, &v.X, &v.Y)
}

func (c *CallCommon) Operands(rands []*Value) []*Value {
	rands = append(rands, &c.Value)
	for i := range c.Args {
		rands = append(rands, &c.Args[i])
	}
	return rands
}

func (s *Go) Operands(rands []*Value) []*Value {
	return s.Call.Operands(rands)
}

func (s *Call) Operands(rands []*Value) []*Value {
	return s.Call.Operands(rands)
}

func (s *Defer) Operands(rands []*Value) []*Value {
	return append(s.Call.Operands(rands), &s._DeferStack)
}

func (v *ChangeInterface) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *ChangeType) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *Convert) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *MultiConvert) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *SliceToArrayPointer) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *SliceToArray) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (s *DebugRef) Operands(rands []*Value) []*Value {
	return append(rands, &s.X)
}

func (s *Copy) Operands(rands []*Value) []*Value {
	return append(rands, &s.X)
}

func (v *Extract) Operands(rands []*Value) []*Value {
	return append(rands, &v.Tuple)
}

func (v *Field) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *FieldAddr) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (s *If) Operands(rands []*Value) []*Value {
	return append(rands, &s.Cond)
}

func (s *ConstantSwitch) Operands(rands []*Value) []*Value {
	rands = append(rands, &s.Tag)
	for i := range s.Conds {
		rands = append(rands, &s.Conds[i])
	}
	return rands
}

func (s *TypeSwitch) Operands(rands []*Value) []*Value {
	rands = append(rands, &s.Tag)
	return rands
}

func (v *Index) Operands(rands []*Value) []*Value {
	return append(rands, &v.X, &v.Index)
}

func (v *IndexAddr) Operands(rands []*Value) []*Value {
	return append(rands, &v.X, &v.Index)
}

func (*Jump) Operands(rands []*Value) []*Value {
	return rands
}

func (*Unreachable) Operands(rands []*Value) []*Value {
	return rands
}

func (v *MapLookup) Operands(rands []*Value) []*Value {
	return append(rands, &v.X, &v.Index)
}

func (v *StringLookup) Operands(rands []*Value) []*Value {
	return append(rands, &v.X, &v.Index)
}

func (v *MakeChan) Operands(rands []*Value) []*Value {
	return append(rands, &v.Size)
}

func (v *MakeClosure) Operands(rands []*Value) []*Value {
	rands = append(rands, &v.Fn)
	for i := range v.Bindings {
		rands = append(rands, &v.Bindings[i])
	}
	return rands
}

func (v *MakeInterface) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *MakeMap) Operands(rands []*Value) []*Value {
	return append(rands, &v.Reserve)
}

func (v *MakeSlice) Operands(rands []*Value) []*Value {
	return append(rands, &v.Len, &v.Cap)
}

func (v *MapUpdate) Operands(rands []*Value) []*Value {
	return append(rands, &v.Map, &v.Key, &v.Value)
}

func (v *Next) Operands(rands []*Value) []*Value {
	return append(rands, &v.Iter)
}

func (s *Panic) Operands(rands []*Value) []*Value {
	return append(rands, &s.X)
}

func (v *Sigma) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *Phi) Operands(rands []*Value) []*Value {
	for i := range v.Edges {
		rands = append(rands, &v.Edges[i])
	}
	return rands
}

func (v *Range) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (s *Return) Operands(rands []*Value) []*Value {
	for i := range s.Results {
		rands = append(rands, &s.Results[i])
	}
	return rands
}

func (*RunDefers) Operands(rands []*Value) []*Value {
	return rands
}

func (v *Select) Operands(rands []*Value) []*Value {
	for i := range v.States {
		rands = append(rands, &v.States[i].Chan, &v.States[i].Send)
	}
	return rands
}

func (s *Send) Operands(rands []*Value) []*Value {
	return append(rands, &s.Chan, &s.X)
}

func (recv *Recv) Operands(rands []*Value) []*Value {
	return append(rands, &recv.Chan)
}

func (v *Slice) Operands(rands []*Value) []*Value {
	return append(rands, &v.X, &v.Low, &v.High, &v.Max)
}

func (s *Store) Operands(rands []*Value) []*Value {
	return append(rands, &s.Addr, &s.Val)
}

func (s *BlankStore) Operands(rands []*Value) []*Value {
	return append(rands, &s.Val)
}

func (v *TypeAssert) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *UnOp) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *Load) Operands(rands []*Value) []*Value {
	return append(rands, &v.X)
}

func (v *AggregateConst) Operands(rands []*Value) []*Value {
	for i := range v.Values {
		rands = append(rands, &v.Values[i])
	}
	return rands
}

func (v *CompositeValue) Operands(rands []*Value) []*Value {
	for i := range v.Values {
		rands = append(rands, &v.Values[i])
	}
	return rands
}

// Non-Instruction Values:
func (v *Builtin) Operands(rands []*Value) []*Value      { return rands }
func (v *FreeVar) Operands(rands []*Value) []*Value      { return rands }
func (v *Const) Operands(rands []*Value) []*Value        { return rands }
func (v *ArrayConst) Operands(rands []*Value) []*Value   { return rands }
func (v *GenericConst) Operands(rands []*Value) []*Value { return rands }
func (v *Function) Operands(rands []*Value) []*Value     { return rands }
func (v *Global) Operands(rands []*Value) []*Value       { return rands }
func (v *Parameter) Operands(rands []*Value) []*Value    { return rands }
