Source file src/cmd/compile/internal/ir/expr.go

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ir
     6  
     7  import (
     8  	"bytes"
     9  	"cmd/compile/internal/base"
    10  	"cmd/compile/internal/types"
    11  	"cmd/internal/obj"
    12  	"cmd/internal/src"
    13  	"fmt"
    14  	"go/constant"
    15  	"go/token"
    16  )
    17  
    18  // An Expr is a Node that can appear as an expression.
    19  type Expr interface {
    20  	Node
    21  	isExpr()
    22  }
    23  
    24  // A miniExpr is a miniNode with extra fields common to expressions.
    25  // TODO(rsc): Once we are sure about the contents, compact the bools
    26  // into a bit field and leave extra bits available for implementations
    27  // embedding miniExpr. Right now there are ~24 unused bits sitting here.
    28  type miniExpr struct {
    29  	miniNode
    30  	flags bitset8
    31  	typ   *types.Type
    32  	init  Nodes // TODO(rsc): Don't require every Node to have an init
    33  }
    34  
    35  const (
    36  	miniExprNonNil = 1 << iota
    37  	miniExprTransient
    38  	miniExprBounded
    39  	miniExprImplicit // for use by implementations; not supported by every Expr
    40  	miniExprCheckPtr
    41  )
    42  
    43  func (*miniExpr) isExpr() {}
    44  
    45  func (n *miniExpr) Type() *types.Type     { return n.typ }
    46  func (n *miniExpr) SetType(x *types.Type) { n.typ = x }
    47  func (n *miniExpr) NonNil() bool          { return n.flags&miniExprNonNil != 0 }
    48  func (n *miniExpr) MarkNonNil()           { n.flags |= miniExprNonNil }
    49  func (n *miniExpr) Transient() bool       { return n.flags&miniExprTransient != 0 }
    50  func (n *miniExpr) SetTransient(b bool)   { n.flags.set(miniExprTransient, b) }
    51  func (n *miniExpr) Bounded() bool         { return n.flags&miniExprBounded != 0 }
    52  func (n *miniExpr) SetBounded(b bool)     { n.flags.set(miniExprBounded, b) }
    53  func (n *miniExpr) Init() Nodes           { return n.init }
    54  func (n *miniExpr) PtrInit() *Nodes       { return &n.init }
    55  func (n *miniExpr) SetInit(x Nodes)       { n.init = x }
    56  
    57  // An AddStringExpr is a string concatenation List[0] + List[1] + ... + List[len(List)-1].
    58  type AddStringExpr struct {
    59  	miniExpr
    60  	List     Nodes
    61  	Prealloc *Name
    62  }
    63  
    64  func NewAddStringExpr(pos src.XPos, list []Node) *AddStringExpr {
    65  	n := &AddStringExpr{}
    66  	n.pos = pos
    67  	n.op = OADDSTR
    68  	n.List = list
    69  	return n
    70  }
    71  
    72  // An AddrExpr is an address-of expression &X.
    73  // It may end up being a normal address-of or an allocation of a composite literal.
    74  type AddrExpr struct {
    75  	miniExpr
    76  	X        Node
    77  	Prealloc *Name // preallocated storage if any
    78  }
    79  
    80  func NewAddrExpr(pos src.XPos, x Node) *AddrExpr {
    81  	if x == nil || x.Typecheck() != 1 {
    82  		base.FatalfAt(pos, "missed typecheck: %L", x)
    83  	}
    84  	n := &AddrExpr{X: x}
    85  	n.pos = pos
    86  
    87  	switch x.Op() {
    88  	case OARRAYLIT, OMAPLIT, OSLICELIT, OSTRUCTLIT:
    89  		n.op = OPTRLIT
    90  
    91  	default:
    92  		n.op = OADDR
    93  		if r, ok := OuterValue(x).(*Name); ok && r.Op() == ONAME {
    94  			r.SetAddrtaken(true)
    95  
    96  			// If r is a closure variable, we need to mark its canonical
    97  			// variable as addrtaken too, so that closure conversion
    98  			// captures it by reference.
    99  			//
   100  			// Exception: if we've already marked the variable as
   101  			// capture-by-value, then that means this variable isn't
   102  			// logically modified, and we must be taking its address to pass
   103  			// to a runtime function that won't mutate it. In that case, we
   104  			// only need to make sure our own copy is addressable.
   105  			if r.IsClosureVar() && !r.Byval() {
   106  				r.Canonical().SetAddrtaken(true)
   107  			}
   108  		}
   109  	}
   110  
   111  	n.SetType(types.NewPtr(x.Type()))
   112  	n.SetTypecheck(1)
   113  
   114  	return n
   115  }
   116  
   117  func (n *AddrExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
   118  func (n *AddrExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
   119  
   120  func (n *AddrExpr) SetOp(op Op) {
   121  	switch op {
   122  	default:
   123  		panic(n.no("SetOp " + op.String()))
   124  	case OADDR, OPTRLIT:
   125  		n.op = op
   126  	}
   127  }
   128  
   129  // A BasicLit is a literal of basic type.
   130  type BasicLit struct {
   131  	miniExpr
   132  	val constant.Value
   133  }
   134  
   135  // NewBasicLit returns an OLITERAL representing val with the given type.
   136  func NewBasicLit(pos src.XPos, typ *types.Type, val constant.Value) Node {
   137  	AssertValidTypeForConst(typ, val)
   138  
   139  	n := &BasicLit{val: val}
   140  	n.op = OLITERAL
   141  	n.pos = pos
   142  	n.SetType(typ)
   143  	n.SetTypecheck(1)
   144  	return n
   145  }
   146  
   147  func (n *BasicLit) Val() constant.Value       { return n.val }
   148  func (n *BasicLit) SetVal(val constant.Value) { n.val = val }
   149  
   150  // NewConstExpr returns an OLITERAL representing val, copying the
   151  // position and type from orig.
   152  func NewConstExpr(val constant.Value, orig Node) Node {
   153  	return NewBasicLit(orig.Pos(), orig.Type(), val)
   154  }
   155  
   156  // A BinaryExpr is a binary expression X Op Y,
   157  // or Op(X, Y) for builtin functions that do not become calls.
   158  type BinaryExpr struct {
   159  	miniExpr
   160  	X     Node
   161  	Y     Node
   162  	RType Node `mknode:"-"` // see reflectdata/helpers.go
   163  }
   164  
   165  func NewBinaryExpr(pos src.XPos, op Op, x, y Node) *BinaryExpr {
   166  	n := &BinaryExpr{X: x, Y: y}
   167  	n.pos = pos
   168  	n.SetOp(op)
   169  	return n
   170  }
   171  
   172  func (n *BinaryExpr) SetOp(op Op) {
   173  	switch op {
   174  	default:
   175  		panic(n.no("SetOp " + op.String()))
   176  	case OADD, OADDSTR, OAND, OANDNOT, ODIV, OEQ, OGE, OGT, OLE,
   177  		OLSH, OLT, OMOD, OMUL, ONE, OOR, ORSH, OSUB, OXOR,
   178  		OCOPY, OCOMPLEX, OUNSAFEADD, OUNSAFESLICE, OUNSAFESTRING,
   179  		OMAKEFACE:
   180  		n.op = op
   181  	}
   182  }
   183  
   184  // A CallExpr is a function call Fun(Args).
   185  type CallExpr struct {
   186  	miniExpr
   187  	Fun       Node
   188  	Args      Nodes
   189  	DeferAt   Node
   190  	RType     Node    `mknode:"-"` // see reflectdata/helpers.go
   191  	KeepAlive []*Name // vars to be kept alive until call returns
   192  	IsDDD     bool
   193  	GoDefer   bool // whether this call is part of a go or defer statement
   194  	NoInline  bool // whether this call must not be inlined
   195  }
   196  
   197  func NewCallExpr(pos src.XPos, op Op, fun Node, args []Node) *CallExpr {
   198  	n := &CallExpr{Fun: fun}
   199  	n.pos = pos
   200  	n.SetOp(op)
   201  	n.Args = args
   202  	return n
   203  }
   204  
   205  func (*CallExpr) isStmt() {}
   206  
   207  func (n *CallExpr) SetOp(op Op) {
   208  	switch op {
   209  	default:
   210  		panic(n.no("SetOp " + op.String()))
   211  	case OAPPEND,
   212  		OCALL, OCALLFUNC, OCALLINTER, OCALLMETH,
   213  		ODELETE,
   214  		OGETG, OGETCALLERSP,
   215  		OMAKE, OMAX, OMIN, OPRINT, OPRINTLN,
   216  		ORECOVER, ORECOVERFP:
   217  		n.op = op
   218  	}
   219  }
   220  
   221  // A ClosureExpr is a function literal expression.
   222  type ClosureExpr struct {
   223  	miniExpr
   224  	Func     *Func `mknode:"-"`
   225  	Prealloc *Name
   226  	IsGoWrap bool // whether this is wrapper closure of a go statement
   227  }
   228  
   229  // A CompLitExpr is a composite literal Type{Vals}.
   230  // Before type-checking, the type is Ntype.
   231  type CompLitExpr struct {
   232  	miniExpr
   233  	List     Nodes // initialized values
   234  	RType    Node  `mknode:"-"` // *runtime._type for OMAPLIT map types
   235  	Prealloc *Name
   236  	// For OSLICELIT, Len is the backing array length.
   237  	// For OMAPLIT, Len is the number of entries that we've removed from List and
   238  	// generated explicit mapassign calls for. This is used to inform the map alloc hint.
   239  	Len int64
   240  }
   241  
   242  func NewCompLitExpr(pos src.XPos, op Op, typ *types.Type, list []Node) *CompLitExpr {
   243  	n := &CompLitExpr{List: list}
   244  	n.pos = pos
   245  	n.SetOp(op)
   246  	if typ != nil {
   247  		n.SetType(typ)
   248  	}
   249  	return n
   250  }
   251  
   252  func (n *CompLitExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
   253  func (n *CompLitExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
   254  
   255  func (n *CompLitExpr) SetOp(op Op) {
   256  	switch op {
   257  	default:
   258  		panic(n.no("SetOp " + op.String()))
   259  	case OARRAYLIT, OCOMPLIT, OMAPLIT, OSTRUCTLIT, OSLICELIT:
   260  		n.op = op
   261  	}
   262  }
   263  
   264  // A ConvExpr is a conversion Type(X).
   265  // It may end up being a value or a type.
   266  type ConvExpr struct {
   267  	miniExpr
   268  	X Node
   269  
   270  	// For implementing OCONVIFACE expressions.
   271  	//
   272  	// TypeWord is an expression yielding a *runtime._type or
   273  	// *runtime.itab value to go in the type word of the iface/eface
   274  	// result. See reflectdata.ConvIfaceTypeWord for further details.
   275  	//
   276  	// SrcRType is an expression yielding a *runtime._type value for X,
   277  	// if it's not pointer-shaped and needs to be heap allocated.
   278  	TypeWord Node `mknode:"-"`
   279  	SrcRType Node `mknode:"-"`
   280  
   281  	// For -d=checkptr instrumentation of conversions from
   282  	// unsafe.Pointer to *Elem or *[Len]Elem.
   283  	//
   284  	// TODO(mdempsky): We only ever need one of these, but currently we
   285  	// don't decide which one until walk. Longer term, it probably makes
   286  	// sense to have a dedicated IR op for `(*[Len]Elem)(ptr)[:n:m]`
   287  	// expressions.
   288  	ElemRType     Node `mknode:"-"`
   289  	ElemElemRType Node `mknode:"-"`
   290  }
   291  
   292  func NewConvExpr(pos src.XPos, op Op, typ *types.Type, x Node) *ConvExpr {
   293  	n := &ConvExpr{X: x}
   294  	n.pos = pos
   295  	n.typ = typ
   296  	n.SetOp(op)
   297  	return n
   298  }
   299  
   300  func (n *ConvExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
   301  func (n *ConvExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
   302  func (n *ConvExpr) CheckPtr() bool     { return n.flags&miniExprCheckPtr != 0 }
   303  func (n *ConvExpr) SetCheckPtr(b bool) { n.flags.set(miniExprCheckPtr, b) }
   304  
   305  func (n *ConvExpr) SetOp(op Op) {
   306  	switch op {
   307  	default:
   308  		panic(n.no("SetOp " + op.String()))
   309  	case OCONV, OCONVIFACE, OCONVNOP, OBYTES2STR, OBYTES2STRTMP, ORUNES2STR, OSTR2BYTES, OSTR2BYTESTMP, OSTR2RUNES, ORUNESTR, OSLICE2ARR, OSLICE2ARRPTR:
   310  		n.op = op
   311  	}
   312  }
   313  
   314  // An IndexExpr is an index expression X[Index].
   315  type IndexExpr struct {
   316  	miniExpr
   317  	X        Node
   318  	Index    Node
   319  	RType    Node `mknode:"-"` // see reflectdata/helpers.go
   320  	Assigned bool
   321  }
   322  
   323  func NewIndexExpr(pos src.XPos, x, index Node) *IndexExpr {
   324  	n := &IndexExpr{X: x, Index: index}
   325  	n.pos = pos
   326  	n.op = OINDEX
   327  	return n
   328  }
   329  
   330  func (n *IndexExpr) SetOp(op Op) {
   331  	switch op {
   332  	default:
   333  		panic(n.no("SetOp " + op.String()))
   334  	case OINDEX, OINDEXMAP:
   335  		n.op = op
   336  	}
   337  }
   338  
   339  // A KeyExpr is a Key: Value composite literal key.
   340  type KeyExpr struct {
   341  	miniExpr
   342  	Key   Node
   343  	Value Node
   344  }
   345  
   346  func NewKeyExpr(pos src.XPos, key, value Node) *KeyExpr {
   347  	n := &KeyExpr{Key: key, Value: value}
   348  	n.pos = pos
   349  	n.op = OKEY
   350  	return n
   351  }
   352  
   353  // A StructKeyExpr is a Field: Value composite literal key.
   354  type StructKeyExpr struct {
   355  	miniExpr
   356  	Field *types.Field
   357  	Value Node
   358  }
   359  
   360  func NewStructKeyExpr(pos src.XPos, field *types.Field, value Node) *StructKeyExpr {
   361  	n := &StructKeyExpr{Field: field, Value: value}
   362  	n.pos = pos
   363  	n.op = OSTRUCTKEY
   364  	return n
   365  }
   366  
   367  func (n *StructKeyExpr) Sym() *types.Sym { return n.Field.Sym }
   368  
   369  // An InlinedCallExpr is an inlined function call.
   370  type InlinedCallExpr struct {
   371  	miniExpr
   372  	Body       Nodes
   373  	ReturnVars Nodes // must be side-effect free
   374  }
   375  
   376  func NewInlinedCallExpr(pos src.XPos, body, retvars []Node) *InlinedCallExpr {
   377  	n := &InlinedCallExpr{}
   378  	n.pos = pos
   379  	n.op = OINLCALL
   380  	n.Body = body
   381  	n.ReturnVars = retvars
   382  	return n
   383  }
   384  
   385  func (n *InlinedCallExpr) SingleResult() Node {
   386  	if have := len(n.ReturnVars); have != 1 {
   387  		base.FatalfAt(n.Pos(), "inlined call has %v results, expected 1", have)
   388  	}
   389  	if !n.Type().HasShape() && n.ReturnVars[0].Type().HasShape() {
   390  		// If the type of the call is not a shape, but the type of the return value
   391  		// is a shape, we need to do an implicit conversion, so the real type
   392  		// of n is maintained.
   393  		r := NewConvExpr(n.Pos(), OCONVNOP, n.Type(), n.ReturnVars[0])
   394  		r.SetTypecheck(1)
   395  		return r
   396  	}
   397  	return n.ReturnVars[0]
   398  }
   399  
   400  // A LogicalExpr is an expression X Op Y where Op is && or ||.
   401  // It is separate from BinaryExpr to make room for statements
   402  // that must be executed before Y but after X.
   403  type LogicalExpr struct {
   404  	miniExpr
   405  	X Node
   406  	Y Node
   407  }
   408  
   409  func NewLogicalExpr(pos src.XPos, op Op, x, y Node) *LogicalExpr {
   410  	n := &LogicalExpr{X: x, Y: y}
   411  	n.pos = pos
   412  	n.SetOp(op)
   413  	return n
   414  }
   415  
   416  func (n *LogicalExpr) SetOp(op Op) {
   417  	switch op {
   418  	default:
   419  		panic(n.no("SetOp " + op.String()))
   420  	case OANDAND, OOROR:
   421  		n.op = op
   422  	}
   423  }
   424  
   425  // A MakeExpr is a make expression: make(Type[, Len[, Cap]]).
   426  // Op is OMAKECHAN, OMAKEMAP, OMAKESLICE, or OMAKESLICECOPY,
   427  // but *not* OMAKE (that's a pre-typechecking CallExpr).
   428  type MakeExpr struct {
   429  	miniExpr
   430  	RType Node `mknode:"-"` // see reflectdata/helpers.go
   431  	Len   Node
   432  	Cap   Node
   433  }
   434  
   435  func NewMakeExpr(pos src.XPos, op Op, len, cap Node) *MakeExpr {
   436  	n := &MakeExpr{Len: len, Cap: cap}
   437  	n.pos = pos
   438  	n.SetOp(op)
   439  	return n
   440  }
   441  
   442  func (n *MakeExpr) SetOp(op Op) {
   443  	switch op {
   444  	default:
   445  		panic(n.no("SetOp " + op.String()))
   446  	case OMAKECHAN, OMAKEMAP, OMAKESLICE, OMAKESLICECOPY:
   447  		n.op = op
   448  	}
   449  }
   450  
   451  // A NilExpr represents the predefined untyped constant nil.
   452  type NilExpr struct {
   453  	miniExpr
   454  }
   455  
   456  func NewNilExpr(pos src.XPos, typ *types.Type) *NilExpr {
   457  	if typ == nil {
   458  		base.FatalfAt(pos, "missing type")
   459  	}
   460  	n := &NilExpr{}
   461  	n.pos = pos
   462  	n.op = ONIL
   463  	n.SetType(typ)
   464  	n.SetTypecheck(1)
   465  	return n
   466  }
   467  
   468  // A ParenExpr is a parenthesized expression (X).
   469  // It may end up being a value or a type.
   470  type ParenExpr struct {
   471  	miniExpr
   472  	X Node
   473  }
   474  
   475  func NewParenExpr(pos src.XPos, x Node) *ParenExpr {
   476  	n := &ParenExpr{X: x}
   477  	n.op = OPAREN
   478  	n.pos = pos
   479  	return n
   480  }
   481  
   482  func (n *ParenExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
   483  func (n *ParenExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
   484  
   485  // A ResultExpr represents a direct access to a result.
   486  type ResultExpr struct {
   487  	miniExpr
   488  	Index int64 // index of the result expr.
   489  }
   490  
   491  func NewResultExpr(pos src.XPos, typ *types.Type, index int64) *ResultExpr {
   492  	n := &ResultExpr{Index: index}
   493  	n.pos = pos
   494  	n.op = ORESULT
   495  	n.typ = typ
   496  	return n
   497  }
   498  
   499  // A LinksymOffsetExpr refers to an offset within a global variable.
   500  // It is like a SelectorExpr but without the field name.
   501  type LinksymOffsetExpr struct {
   502  	miniExpr
   503  	Linksym *obj.LSym
   504  	Offset_ int64
   505  }
   506  
   507  func NewLinksymOffsetExpr(pos src.XPos, lsym *obj.LSym, offset int64, typ *types.Type) *LinksymOffsetExpr {
   508  	if typ == nil {
   509  		base.FatalfAt(pos, "nil type")
   510  	}
   511  	n := &LinksymOffsetExpr{Linksym: lsym, Offset_: offset}
   512  	n.typ = typ
   513  	n.op = OLINKSYMOFFSET
   514  	n.SetTypecheck(1)
   515  	return n
   516  }
   517  
   518  // NewLinksymExpr is NewLinksymOffsetExpr, but with offset fixed at 0.
   519  func NewLinksymExpr(pos src.XPos, lsym *obj.LSym, typ *types.Type) *LinksymOffsetExpr {
   520  	return NewLinksymOffsetExpr(pos, lsym, 0, typ)
   521  }
   522  
   523  // NewNameOffsetExpr is NewLinksymOffsetExpr, but taking a *Name
   524  // representing a global variable instead of an *obj.LSym directly.
   525  func NewNameOffsetExpr(pos src.XPos, name *Name, offset int64, typ *types.Type) *LinksymOffsetExpr {
   526  	if name == nil || IsBlank(name) || !(name.Op() == ONAME && name.Class == PEXTERN) {
   527  		base.FatalfAt(pos, "cannot take offset of nil, blank name or non-global variable: %v", name)
   528  	}
   529  	return NewLinksymOffsetExpr(pos, name.Linksym(), offset, typ)
   530  }
   531  
   532  // A SelectorExpr is a selector expression X.Sel.
   533  type SelectorExpr struct {
   534  	miniExpr
   535  	X Node
   536  	// Sel is the name of the field or method being selected, without (in the
   537  	// case of methods) any preceding type specifier. If the field/method is
   538  	// exported, than the Sym uses the local package regardless of the package
   539  	// of the containing type.
   540  	Sel *types.Sym
   541  	// The actual selected field - may not be filled in until typechecking.
   542  	Selection *types.Field
   543  	Prealloc  *Name // preallocated storage for OMETHVALUE, if any
   544  }
   545  
   546  func NewSelectorExpr(pos src.XPos, op Op, x Node, sel *types.Sym) *SelectorExpr {
   547  	n := &SelectorExpr{X: x, Sel: sel}
   548  	n.pos = pos
   549  	n.SetOp(op)
   550  	return n
   551  }
   552  
   553  func (n *SelectorExpr) SetOp(op Op) {
   554  	switch op {
   555  	default:
   556  		panic(n.no("SetOp " + op.String()))
   557  	case OXDOT, ODOT, ODOTPTR, ODOTMETH, ODOTINTER, OMETHVALUE, OMETHEXPR:
   558  		n.op = op
   559  	}
   560  }
   561  
   562  func (n *SelectorExpr) Sym() *types.Sym    { return n.Sel }
   563  func (n *SelectorExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
   564  func (n *SelectorExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
   565  func (n *SelectorExpr) Offset() int64      { return n.Selection.Offset }
   566  
   567  func (n *SelectorExpr) FuncName() *Name {
   568  	if n.Op() != OMETHEXPR {
   569  		panic(n.no("FuncName"))
   570  	}
   571  	fn := NewNameAt(n.Selection.Pos, MethodSym(n.X.Type(), n.Sel), n.Type())
   572  	fn.Class = PFUNC
   573  	if n.Selection.Nname != nil {
   574  		// TODO(austin): Nname is nil for interface method
   575  		// expressions (I.M), so we can't attach a Func to
   576  		// those here.
   577  		fn.Func = n.Selection.Nname.(*Name).Func
   578  	}
   579  	return fn
   580  }
   581  
   582  // A SliceExpr is a slice expression X[Low:High] or X[Low:High:Max].
   583  type SliceExpr struct {
   584  	miniExpr
   585  	X    Node
   586  	Low  Node
   587  	High Node
   588  	Max  Node
   589  }
   590  
   591  func NewSliceExpr(pos src.XPos, op Op, x, low, high, max Node) *SliceExpr {
   592  	n := &SliceExpr{X: x, Low: low, High: high, Max: max}
   593  	n.pos = pos
   594  	n.op = op
   595  	return n
   596  }
   597  
   598  func (n *SliceExpr) SetOp(op Op) {
   599  	switch op {
   600  	default:
   601  		panic(n.no("SetOp " + op.String()))
   602  	case OSLICE, OSLICEARR, OSLICESTR, OSLICE3, OSLICE3ARR:
   603  		n.op = op
   604  	}
   605  }
   606  
   607  // IsSlice3 reports whether o is a slice3 op (OSLICE3, OSLICE3ARR).
   608  // o must be a slicing op.
   609  func (o Op) IsSlice3() bool {
   610  	switch o {
   611  	case OSLICE, OSLICEARR, OSLICESTR:
   612  		return false
   613  	case OSLICE3, OSLICE3ARR:
   614  		return true
   615  	}
   616  	base.Fatalf("IsSlice3 op %v", o)
   617  	return false
   618  }
   619  
   620  // A SliceHeader expression constructs a slice header from its parts.
   621  type SliceHeaderExpr struct {
   622  	miniExpr
   623  	Ptr Node
   624  	Len Node
   625  	Cap Node
   626  }
   627  
   628  func NewSliceHeaderExpr(pos src.XPos, typ *types.Type, ptr, len, cap Node) *SliceHeaderExpr {
   629  	n := &SliceHeaderExpr{Ptr: ptr, Len: len, Cap: cap}
   630  	n.pos = pos
   631  	n.op = OSLICEHEADER
   632  	n.typ = typ
   633  	return n
   634  }
   635  
   636  // A StringHeaderExpr expression constructs a string header from its parts.
   637  type StringHeaderExpr struct {
   638  	miniExpr
   639  	Ptr Node
   640  	Len Node
   641  }
   642  
   643  func NewStringHeaderExpr(pos src.XPos, ptr, len Node) *StringHeaderExpr {
   644  	n := &StringHeaderExpr{Ptr: ptr, Len: len}
   645  	n.pos = pos
   646  	n.op = OSTRINGHEADER
   647  	n.typ = types.Types[types.TSTRING]
   648  	return n
   649  }
   650  
   651  // A StarExpr is a dereference expression *X.
   652  // It may end up being a value or a type.
   653  type StarExpr struct {
   654  	miniExpr
   655  	X Node
   656  }
   657  
   658  func NewStarExpr(pos src.XPos, x Node) *StarExpr {
   659  	n := &StarExpr{X: x}
   660  	n.op = ODEREF
   661  	n.pos = pos
   662  	return n
   663  }
   664  
   665  func (n *StarExpr) Implicit() bool     { return n.flags&miniExprImplicit != 0 }
   666  func (n *StarExpr) SetImplicit(b bool) { n.flags.set(miniExprImplicit, b) }
   667  
   668  // A TypeAssertionExpr is a selector expression X.(Type).
   669  // Before type-checking, the type is Ntype.
   670  type TypeAssertExpr struct {
   671  	miniExpr
   672  	X Node
   673  
   674  	// Runtime type information provided by walkDotType for
   675  	// assertions from non-empty interface to concrete type.
   676  	ITab Node `mknode:"-"` // *runtime.itab for Type implementing X's type
   677  
   678  	// An internal/abi.TypeAssert descriptor to pass to the runtime.
   679  	Descriptor *obj.LSym
   680  }
   681  
   682  func NewTypeAssertExpr(pos src.XPos, x Node, typ *types.Type) *TypeAssertExpr {
   683  	n := &TypeAssertExpr{X: x}
   684  	n.pos = pos
   685  	n.op = ODOTTYPE
   686  	if typ != nil {
   687  		n.SetType(typ)
   688  	}
   689  	return n
   690  }
   691  
   692  func (n *TypeAssertExpr) SetOp(op Op) {
   693  	switch op {
   694  	default:
   695  		panic(n.no("SetOp " + op.String()))
   696  	case ODOTTYPE, ODOTTYPE2:
   697  		n.op = op
   698  	}
   699  }
   700  
   701  // A DynamicTypeAssertExpr asserts that X is of dynamic type RType.
   702  type DynamicTypeAssertExpr struct {
   703  	miniExpr
   704  	X Node
   705  
   706  	// SrcRType is an expression that yields a *runtime._type value
   707  	// representing X's type. It's used in failed assertion panic
   708  	// messages.
   709  	SrcRType Node
   710  
   711  	// RType is an expression that yields a *runtime._type value
   712  	// representing the asserted type.
   713  	//
   714  	// BUG(mdempsky): If ITab is non-nil, RType may be nil.
   715  	RType Node
   716  
   717  	// ITab is an expression that yields a *runtime.itab value
   718  	// representing the asserted type within the assertee expression's
   719  	// original interface type.
   720  	//
   721  	// ITab is only used for assertions from non-empty interface type to
   722  	// a concrete (i.e., non-interface) type. For all other assertions,
   723  	// ITab is nil.
   724  	ITab Node
   725  }
   726  
   727  func NewDynamicTypeAssertExpr(pos src.XPos, op Op, x, rtype Node) *DynamicTypeAssertExpr {
   728  	n := &DynamicTypeAssertExpr{X: x, RType: rtype}
   729  	n.pos = pos
   730  	n.op = op
   731  	return n
   732  }
   733  
   734  func (n *DynamicTypeAssertExpr) SetOp(op Op) {
   735  	switch op {
   736  	default:
   737  		panic(n.no("SetOp " + op.String()))
   738  	case ODYNAMICDOTTYPE, ODYNAMICDOTTYPE2:
   739  		n.op = op
   740  	}
   741  }
   742  
   743  // A UnaryExpr is a unary expression Op X,
   744  // or Op(X) for a builtin function that does not end up being a call.
   745  type UnaryExpr struct {
   746  	miniExpr
   747  	X Node
   748  }
   749  
   750  func NewUnaryExpr(pos src.XPos, op Op, x Node) *UnaryExpr {
   751  	n := &UnaryExpr{X: x}
   752  	n.pos = pos
   753  	n.SetOp(op)
   754  	return n
   755  }
   756  
   757  func (n *UnaryExpr) SetOp(op Op) {
   758  	switch op {
   759  	default:
   760  		panic(n.no("SetOp " + op.String()))
   761  	case OBITNOT, ONEG, ONOT, OPLUS, ORECV,
   762  		OCAP, OCLEAR, OCLOSE, OIMAG, OLEN, ONEW, OPANIC, OREAL,
   763  		OCHECKNIL, OCFUNC, OIDATA, OITAB, OSPTR,
   764  		OUNSAFESTRINGDATA, OUNSAFESLICEDATA:
   765  		n.op = op
   766  	}
   767  }
   768  
   769  func IsZero(n Node) bool {
   770  	switch n.Op() {
   771  	case ONIL:
   772  		return true
   773  
   774  	case OLITERAL:
   775  		switch u := n.Val(); u.Kind() {
   776  		case constant.String:
   777  			return constant.StringVal(u) == ""
   778  		case constant.Bool:
   779  			return !constant.BoolVal(u)
   780  		default:
   781  			return constant.Sign(u) == 0
   782  		}
   783  
   784  	case OARRAYLIT:
   785  		n := n.(*CompLitExpr)
   786  		for _, n1 := range n.List {
   787  			if n1.Op() == OKEY {
   788  				n1 = n1.(*KeyExpr).Value
   789  			}
   790  			if !IsZero(n1) {
   791  				return false
   792  			}
   793  		}
   794  		return true
   795  
   796  	case OSTRUCTLIT:
   797  		n := n.(*CompLitExpr)
   798  		for _, n1 := range n.List {
   799  			n1 := n1.(*StructKeyExpr)
   800  			if !IsZero(n1.Value) {
   801  				return false
   802  			}
   803  		}
   804  		return true
   805  	}
   806  
   807  	return false
   808  }
   809  
   810  // lvalue etc
   811  func IsAddressable(n Node) bool {
   812  	switch n.Op() {
   813  	case OINDEX:
   814  		n := n.(*IndexExpr)
   815  		if n.X.Type() != nil && n.X.Type().IsArray() {
   816  			return IsAddressable(n.X)
   817  		}
   818  		if n.X.Type() != nil && n.X.Type().IsString() {
   819  			return false
   820  		}
   821  		fallthrough
   822  	case ODEREF, ODOTPTR:
   823  		return true
   824  
   825  	case ODOT:
   826  		n := n.(*SelectorExpr)
   827  		return IsAddressable(n.X)
   828  
   829  	case ONAME:
   830  		n := n.(*Name)
   831  		if n.Class == PFUNC {
   832  			return false
   833  		}
   834  		return true
   835  
   836  	case OLINKSYMOFFSET:
   837  		return true
   838  	}
   839  
   840  	return false
   841  }
   842  
   843  // StaticValue analyzes n to find the earliest expression that always
   844  // evaluates to the same value as n, which might be from an enclosing
   845  // function.
   846  //
   847  // For example, given:
   848  //
   849  //	var x int = g()
   850  //	func() {
   851  //		y := x
   852  //		*p = int(y)
   853  //	}
   854  //
   855  // calling StaticValue on the "int(y)" expression returns the outer
   856  // "g()" expression.
   857  //
   858  // NOTE: StaticValue can return a result with a different type than
   859  // n's type because it can traverse through OCONVNOP operations.
   860  // TODO: consider reapplying OCONVNOP operations to the result. See https://go.dev/cl/676517.
   861  func StaticValue(n Node) Node {
   862  	for {
   863  		switch n1 := n.(type) {
   864  		case *ConvExpr:
   865  			if n1.Op() == OCONVNOP {
   866  				n = n1.X
   867  				continue
   868  			}
   869  		case *InlinedCallExpr:
   870  			if n1.Op() == OINLCALL {
   871  				n = n1.SingleResult()
   872  				continue
   873  			}
   874  		case *ParenExpr:
   875  			n = n1.X
   876  			continue
   877  		}
   878  
   879  		n1 := staticValue1(n)
   880  		if n1 == nil {
   881  			return n
   882  		}
   883  		n = n1
   884  	}
   885  }
   886  
   887  func staticValue1(nn Node) Node {
   888  	if nn.Op() != ONAME {
   889  		return nil
   890  	}
   891  	n := nn.(*Name).Canonical()
   892  	if n.Class != PAUTO {
   893  		return nil
   894  	}
   895  
   896  	defn := n.Defn
   897  	if defn == nil {
   898  		return nil
   899  	}
   900  
   901  	var rhs Node
   902  FindRHS:
   903  	switch defn.Op() {
   904  	case OAS:
   905  		defn := defn.(*AssignStmt)
   906  		rhs = defn.Y
   907  	case OAS2:
   908  		defn := defn.(*AssignListStmt)
   909  		for i, lhs := range defn.Lhs {
   910  			if lhs == n {
   911  				rhs = defn.Rhs[i]
   912  				break FindRHS
   913  			}
   914  		}
   915  		base.Fatalf("%v missing from LHS of %v", n, defn)
   916  	default:
   917  		return nil
   918  	}
   919  	if rhs == nil {
   920  		base.Fatalf("RHS is nil: %v", defn)
   921  	}
   922  
   923  	if Reassigned(n) {
   924  		return nil
   925  	}
   926  
   927  	return rhs
   928  }
   929  
   930  // Reassigned takes an ONAME node, walks the function in which it is
   931  // defined, and returns a boolean indicating whether the name has any
   932  // assignments other than its declaration.
   933  // NB: global variables are always considered to be re-assigned.
   934  // TODO: handle initial declaration not including an assignment and
   935  // followed by a single assignment?
   936  // NOTE: any changes made here should also be made in the corresponding
   937  // code in the ReassignOracle.Init method.
   938  func Reassigned(name *Name) bool {
   939  	if name.Op() != ONAME {
   940  		base.Fatalf("reassigned %v", name)
   941  	}
   942  	// no way to reliably check for no-reassignment of globals, assume it can be
   943  	if name.Curfn == nil {
   944  		return true
   945  	}
   946  
   947  	if name.Addrtaken() {
   948  		return true // conservatively assume it's reassigned indirectly
   949  	}
   950  
   951  	// TODO(mdempsky): This is inefficient and becoming increasingly
   952  	// unwieldy. Figure out a way to generalize escape analysis's
   953  	// reassignment detection for use by inlining and devirtualization.
   954  
   955  	// isName reports whether n is a reference to name.
   956  	isName := func(x Node) bool {
   957  		if x == nil {
   958  			return false
   959  		}
   960  		n, ok := OuterValue(x).(*Name)
   961  		return ok && n.Canonical() == name
   962  	}
   963  
   964  	var do func(n Node) bool
   965  	do = func(n Node) bool {
   966  		switch n.Op() {
   967  		case OAS:
   968  			n := n.(*AssignStmt)
   969  			if isName(n.X) && n != name.Defn {
   970  				return true
   971  			}
   972  		case OAS2, OAS2FUNC, OAS2MAPR, OAS2DOTTYPE, OAS2RECV, OSELRECV2:
   973  			n := n.(*AssignListStmt)
   974  			for _, p := range n.Lhs {
   975  				if isName(p) && n != name.Defn {
   976  					return true
   977  				}
   978  			}
   979  		case OASOP:
   980  			n := n.(*AssignOpStmt)
   981  			if isName(n.X) {
   982  				return true
   983  			}
   984  		case OADDR:
   985  			n := n.(*AddrExpr)
   986  			if isName(n.X) {
   987  				base.FatalfAt(n.Pos(), "%v not marked addrtaken", name)
   988  			}
   989  		case ORANGE:
   990  			n := n.(*RangeStmt)
   991  			if isName(n.Key) || isName(n.Value) {
   992  				return true
   993  			}
   994  		case OCLOSURE:
   995  			n := n.(*ClosureExpr)
   996  			if Any(n.Func, do) {
   997  				return true
   998  			}
   999  		}
  1000  		return false
  1001  	}
  1002  	return Any(name.Curfn, do)
  1003  }
  1004  
  1005  // StaticCalleeName returns the ONAME/PFUNC for n, if known.
  1006  func StaticCalleeName(n Node) *Name {
  1007  	switch n.Op() {
  1008  	case OMETHEXPR:
  1009  		n := n.(*SelectorExpr)
  1010  		return MethodExprName(n)
  1011  	case ONAME:
  1012  		n := n.(*Name)
  1013  		if n.Class == PFUNC {
  1014  			return n
  1015  		}
  1016  	case OCLOSURE:
  1017  		return n.(*ClosureExpr).Func.Nname
  1018  	}
  1019  	return nil
  1020  }
  1021  
  1022  // IsIntrinsicCall reports whether the compiler back end will treat the call as an intrinsic operation.
  1023  var IsIntrinsicCall = func(*CallExpr) bool { return false }
  1024  
  1025  // SameSafeExpr checks whether it is safe to reuse one of l and r
  1026  // instead of computing both. SameSafeExpr assumes that l and r are
  1027  // used in the same statement or expression. In order for it to be
  1028  // safe to reuse l or r, they must:
  1029  //   - be the same expression
  1030  //   - not have side-effects (no function calls, no channel ops);
  1031  //     however, panics are ok
  1032  //   - not cause inappropriate aliasing; e.g. two string to []byte
  1033  //     conversions, must result in two distinct slices
  1034  //
  1035  // The handling of OINDEXMAP is subtle. OINDEXMAP can occur both
  1036  // as an lvalue (map assignment) and an rvalue (map access). This is
  1037  // currently OK, since the only place SameSafeExpr gets used on an
  1038  // lvalue expression is for OSLICE and OAPPEND optimizations, and it
  1039  // is correct in those settings.
  1040  func SameSafeExpr(l Node, r Node) bool {
  1041  	for l.Op() == OCONVNOP {
  1042  		l = l.(*ConvExpr).X
  1043  	}
  1044  	for r.Op() == OCONVNOP {
  1045  		r = r.(*ConvExpr).X
  1046  	}
  1047  	if l.Op() != r.Op() || !types.Identical(l.Type(), r.Type()) {
  1048  		return false
  1049  	}
  1050  
  1051  	switch l.Op() {
  1052  	case ONAME:
  1053  		return l == r
  1054  
  1055  	case ODOT, ODOTPTR:
  1056  		l := l.(*SelectorExpr)
  1057  		r := r.(*SelectorExpr)
  1058  		return l.Sel != nil && r.Sel != nil && l.Sel == r.Sel && SameSafeExpr(l.X, r.X)
  1059  
  1060  	case ODEREF:
  1061  		l := l.(*StarExpr)
  1062  		r := r.(*StarExpr)
  1063  		return SameSafeExpr(l.X, r.X)
  1064  
  1065  	case ONOT, OBITNOT, OPLUS, ONEG:
  1066  		l := l.(*UnaryExpr)
  1067  		r := r.(*UnaryExpr)
  1068  		return SameSafeExpr(l.X, r.X)
  1069  
  1070  	case OCONV:
  1071  		l := l.(*ConvExpr)
  1072  		r := r.(*ConvExpr)
  1073  		// Some conversions can't be reused, such as []byte(str).
  1074  		// Allow only numeric-ish types. This is a bit conservative.
  1075  		return types.IsSimple[l.Type().Kind()] && SameSafeExpr(l.X, r.X)
  1076  
  1077  	case OINDEX, OINDEXMAP:
  1078  		l := l.(*IndexExpr)
  1079  		r := r.(*IndexExpr)
  1080  		return SameSafeExpr(l.X, r.X) && SameSafeExpr(l.Index, r.Index)
  1081  
  1082  	case OADD, OSUB, OOR, OXOR, OMUL, OLSH, ORSH, OAND, OANDNOT, ODIV, OMOD:
  1083  		l := l.(*BinaryExpr)
  1084  		r := r.(*BinaryExpr)
  1085  		return SameSafeExpr(l.X, r.X) && SameSafeExpr(l.Y, r.Y)
  1086  
  1087  	case OLITERAL:
  1088  		return constant.Compare(l.Val(), token.EQL, r.Val())
  1089  
  1090  	case ONIL:
  1091  		return true
  1092  	}
  1093  
  1094  	return false
  1095  }
  1096  
  1097  // ShouldCheckPtr reports whether pointer checking should be enabled for
  1098  // function fn at a given level. See debugHelpFooter for defined
  1099  // levels.
  1100  func ShouldCheckPtr(fn *Func, level int) bool {
  1101  	return base.Debug.Checkptr >= level && fn.Pragma&NoCheckPtr == 0
  1102  }
  1103  
  1104  // ShouldAsanCheckPtr reports whether pointer checking should be enabled for
  1105  // function fn when -asan is enabled.
  1106  func ShouldAsanCheckPtr(fn *Func) bool {
  1107  	return base.Flag.ASan && fn.Pragma&NoCheckPtr == 0
  1108  }
  1109  
  1110  // IsReflectHeaderDataField reports whether l is an expression p.Data
  1111  // where p has type reflect.SliceHeader or reflect.StringHeader.
  1112  func IsReflectHeaderDataField(l Node) bool {
  1113  	if l.Type() != types.Types[types.TUINTPTR] {
  1114  		return false
  1115  	}
  1116  
  1117  	var tsym *types.Sym
  1118  	switch l.Op() {
  1119  	case ODOT:
  1120  		l := l.(*SelectorExpr)
  1121  		tsym = l.X.Type().Sym()
  1122  	case ODOTPTR:
  1123  		l := l.(*SelectorExpr)
  1124  		tsym = l.X.Type().Elem().Sym()
  1125  	default:
  1126  		return false
  1127  	}
  1128  
  1129  	if tsym == nil || l.Sym().Name != "Data" || tsym.Pkg.Path != "reflect" {
  1130  		return false
  1131  	}
  1132  	return tsym.Name == "SliceHeader" || tsym.Name == "StringHeader"
  1133  }
  1134  
  1135  func ParamNames(ft *types.Type) []Node {
  1136  	args := make([]Node, ft.NumParams())
  1137  	for i, f := range ft.Params() {
  1138  		args[i] = f.Nname.(*Name)
  1139  	}
  1140  	return args
  1141  }
  1142  
  1143  // MethodSym returns the method symbol representing a method name
  1144  // associated with a specific receiver type.
  1145  //
  1146  // Method symbols can be used to distinguish the same method appearing
  1147  // in different method sets. For example, T.M and (*T).M have distinct
  1148  // method symbols.
  1149  //
  1150  // The returned symbol will be marked as a function.
  1151  func MethodSym(recv *types.Type, msym *types.Sym) *types.Sym {
  1152  	sym := MethodSymSuffix(recv, msym, "")
  1153  	sym.SetFunc(true)
  1154  	return sym
  1155  }
  1156  
  1157  // MethodSymSuffix is like MethodSym, but allows attaching a
  1158  // distinguisher suffix. To avoid collisions, the suffix must not
  1159  // start with a letter, number, or period.
  1160  func MethodSymSuffix(recv *types.Type, msym *types.Sym, suffix string) *types.Sym {
  1161  	if msym.IsBlank() {
  1162  		base.Fatalf("blank method name")
  1163  	}
  1164  
  1165  	rsym := recv.Sym()
  1166  	if recv.IsPtr() {
  1167  		if rsym != nil {
  1168  			base.Fatalf("declared pointer receiver type: %v", recv)
  1169  		}
  1170  		rsym = recv.Elem().Sym()
  1171  	}
  1172  
  1173  	// Find the package the receiver type appeared in. For
  1174  	// anonymous receiver types (i.e., anonymous structs with
  1175  	// embedded fields), use the "go" pseudo-package instead.
  1176  	rpkg := Pkgs.Go
  1177  	if rsym != nil {
  1178  		rpkg = rsym.Pkg
  1179  	}
  1180  
  1181  	var b bytes.Buffer
  1182  	if recv.IsPtr() {
  1183  		// The parentheses aren't really necessary, but
  1184  		// they're pretty traditional at this point.
  1185  		fmt.Fprintf(&b, "(%-S)", recv)
  1186  	} else {
  1187  		fmt.Fprintf(&b, "%-S", recv)
  1188  	}
  1189  
  1190  	// A particular receiver type may have multiple non-exported
  1191  	// methods with the same name. To disambiguate them, include a
  1192  	// package qualifier for names that came from a different
  1193  	// package than the receiver type.
  1194  	if !types.IsExported(msym.Name) && msym.Pkg != rpkg {
  1195  		b.WriteString(".")
  1196  		b.WriteString(msym.Pkg.Prefix)
  1197  	}
  1198  
  1199  	b.WriteString(".")
  1200  	b.WriteString(msym.Name)
  1201  	b.WriteString(suffix)
  1202  	return rpkg.LookupBytes(b.Bytes())
  1203  }
  1204  
  1205  // LookupMethodSelector returns the types.Sym of the selector for a method
  1206  // named in local symbol name, as well as the types.Sym of the receiver.
  1207  //
  1208  // TODO(prattmic): this does not attempt to handle method suffixes (wrappers).
  1209  func LookupMethodSelector(pkg *types.Pkg, name string) (typ, meth *types.Sym, err error) {
  1210  	typeName, methName := splitType(name)
  1211  	if typeName == "" {
  1212  		return nil, nil, fmt.Errorf("%s doesn't contain type split", name)
  1213  	}
  1214  
  1215  	if len(typeName) > 3 && typeName[:2] == "(*" && typeName[len(typeName)-1] == ')' {
  1216  		// Symbol name is for a pointer receiver method. We just want
  1217  		// the base type name.
  1218  		typeName = typeName[2 : len(typeName)-1]
  1219  	}
  1220  
  1221  	typ = pkg.Lookup(typeName)
  1222  	meth = pkg.Selector(methName)
  1223  	return typ, meth, nil
  1224  }
  1225  
  1226  // splitType splits a local symbol name into type and method (fn). If this a
  1227  // free function, typ == "".
  1228  //
  1229  // N.B. closures and methods can be ambiguous (e.g., bar.func1). These cases
  1230  // are returned as methods.
  1231  func splitType(name string) (typ, fn string) {
  1232  	// Types are split on the first dot, ignoring everything inside
  1233  	// brackets (instantiation of type parameter, usually including
  1234  	// "go.shape").
  1235  	bracket := 0
  1236  	for i, r := range name {
  1237  		if r == '.' && bracket == 0 {
  1238  			return name[:i], name[i+1:]
  1239  		}
  1240  		if r == '[' {
  1241  			bracket++
  1242  		}
  1243  		if r == ']' {
  1244  			bracket--
  1245  		}
  1246  	}
  1247  	return "", name
  1248  }
  1249  
  1250  // MethodExprName returns the ONAME representing the method
  1251  // referenced by expression n, which must be a method selector,
  1252  // method expression, or method value.
  1253  func MethodExprName(n Node) *Name {
  1254  	name, _ := MethodExprFunc(n).Nname.(*Name)
  1255  	return name
  1256  }
  1257  
  1258  // MethodExprFunc is like MethodExprName, but returns the types.Field instead.
  1259  func MethodExprFunc(n Node) *types.Field {
  1260  	switch n.Op() {
  1261  	case ODOTMETH, OMETHEXPR, OMETHVALUE:
  1262  		return n.(*SelectorExpr).Selection
  1263  	}
  1264  	base.Fatalf("unexpected node: %v (%v)", n, n.Op())
  1265  	panic("unreachable")
  1266  }
  1267  

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