name.go

Documentation: cmd/compile/internal/ir

     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  	"cmd/compile/internal/base"
     9  	"cmd/compile/internal/types"
    10  	"cmd/internal/obj"
    11  	"cmd/internal/objabi"
    12  	"cmd/internal/src"
    13  	"fmt"
    14  
    15  	"go/constant"
    16  )
    17  
    18  // An Ident is an identifier, possibly qualified.
    19  type Ident struct {
    20  	miniExpr
    21  	sym *types.Sym
    22  }
    23  
    24  func NewIdent(pos src.XPos, sym *types.Sym) *Ident {
    25  	n := new(Ident)
    26  	n.op = ONONAME
    27  	n.pos = pos
    28  	n.sym = sym
    29  	return n
    30  }
    31  
    32  func (n *Ident) Sym() *types.Sym { return n.sym }
    33  
    34  // Name holds Node fields used only by named nodes (ONAME, OTYPE, some OLITERAL).
    35  type Name struct {
    36  	miniExpr
    37  	BuiltinOp Op         // uint8
    38  	Class     Class      // uint8
    39  	pragma    PragmaFlag // int16
    40  	flags     bitset16
    41  	DictIndex uint16 // index of the dictionary entry describing the type of this variable declaration plus 1
    42  	sym       *types.Sym
    43  	Func      *Func // TODO(austin): nil for I.M
    44  	Offset_   int64
    45  	val       constant.Value
    46  	Opt       interface{} // for use by escape analysis
    47  	Embed     *[]Embed    // list of embedded files, for ONAME var
    48  
    49  	// For a local variable (not param) or extern, the initializing assignment (OAS or OAS2).
    50  	// For a closure var, the ONAME node of the original (outermost) captured variable.
    51  	// For the case-local variables of a type switch, the type switch guard (OTYPESW).
    52  	// For a range variable, the range statement (ORANGE)
    53  	// For a recv variable in a case of a select statement, the receive assignment (OSELRECV2)
    54  	// For the name of a function, points to corresponding Func node.
    55  	Defn Node
    56  
    57  	// The function, method, or closure in which local variable or param is declared.
    58  	Curfn *Func
    59  
    60  	Heapaddr *Name // temp holding heap address of param
    61  
    62  	// Outer points to the immediately enclosing function's copy of this
    63  	// closure variable. If not a closure variable, then Outer is nil.
    64  	Outer *Name
    65  }
    66  
    67  func (n *Name) isExpr() {}
    68  
    69  func (n *Name) copy() Node                                  { panic(n.no("copy")) }
    70  func (n *Name) doChildren(do func(Node) bool) bool          { return false }
    71  func (n *Name) editChildren(edit func(Node) Node)           {}
    72  func (n *Name) editChildrenWithHidden(edit func(Node) Node) {}
    73  
    74  // RecordFrameOffset records the frame offset for the name.
    75  // It is used by package types when laying out function arguments.
    76  func (n *Name) RecordFrameOffset(offset int64) {
    77  	n.SetFrameOffset(offset)
    78  }
    79  
    80  // NewNameAt returns a new ONAME Node associated with symbol s at position pos.
    81  // The caller is responsible for setting Curfn.
    82  func NewNameAt(pos src.XPos, sym *types.Sym, typ *types.Type) *Name {
    83  	if sym == nil {
    84  		base.Fatalf("NewNameAt nil")
    85  	}
    86  	n := newNameAt(pos, ONAME, sym)
    87  	if typ != nil {
    88  		n.SetType(typ)
    89  		n.SetTypecheck(1)
    90  	}
    91  	return n
    92  }
    93  
    94  // NewBuiltin returns a new Name representing a builtin function,
    95  // either predeclared or from package unsafe.
    96  func NewBuiltin(sym *types.Sym, op Op) *Name {
    97  	n := newNameAt(src.NoXPos, ONAME, sym)
    98  	n.BuiltinOp = op
    99  	n.SetTypecheck(1)
   100  	sym.Def = n
   101  	return n
   102  }
   103  
   104  // NewLocal returns a new function-local variable with the given name and type.
   105  func (fn *Func) NewLocal(pos src.XPos, sym *types.Sym, typ *types.Type) *Name {
   106  	if fn.Dcl == nil {
   107  		base.FatalfAt(pos, "must call DeclParams on %v first", fn)
   108  	}
   109  
   110  	n := NewNameAt(pos, sym, typ)
   111  	n.Class = PAUTO
   112  	n.Curfn = fn
   113  	fn.Dcl = append(fn.Dcl, n)
   114  	return n
   115  }
   116  
   117  // NewDeclNameAt returns a new Name associated with symbol s at position pos.
   118  // The caller is responsible for setting Curfn.
   119  func NewDeclNameAt(pos src.XPos, op Op, sym *types.Sym) *Name {
   120  	if sym == nil {
   121  		base.Fatalf("NewDeclNameAt nil")
   122  	}
   123  	switch op {
   124  	case ONAME, OTYPE, OLITERAL:
   125  		// ok
   126  	default:
   127  		base.Fatalf("NewDeclNameAt op %v", op)
   128  	}
   129  	return newNameAt(pos, op, sym)
   130  }
   131  
   132  // NewConstAt returns a new OLITERAL Node associated with symbol s at position pos.
   133  func NewConstAt(pos src.XPos, sym *types.Sym, typ *types.Type, val constant.Value) *Name {
   134  	if sym == nil {
   135  		base.Fatalf("NewConstAt nil")
   136  	}
   137  	n := newNameAt(pos, OLITERAL, sym)
   138  	n.SetType(typ)
   139  	n.SetTypecheck(1)
   140  	n.SetVal(val)
   141  	return n
   142  }
   143  
   144  // newNameAt is like NewNameAt but allows sym == nil.
   145  func newNameAt(pos src.XPos, op Op, sym *types.Sym) *Name {
   146  	n := new(Name)
   147  	n.op = op
   148  	n.pos = pos
   149  	n.sym = sym
   150  	return n
   151  }
   152  
   153  func (n *Name) Name() *Name            { return n }
   154  func (n *Name) Sym() *types.Sym        { return n.sym }
   155  func (n *Name) SetSym(x *types.Sym)    { n.sym = x }
   156  func (n *Name) SubOp() Op              { return n.BuiltinOp }
   157  func (n *Name) SetSubOp(x Op)          { n.BuiltinOp = x }
   158  func (n *Name) SetFunc(x *Func)        { n.Func = x }
   159  func (n *Name) FrameOffset() int64     { return n.Offset_ }
   160  func (n *Name) SetFrameOffset(x int64) { n.Offset_ = x }
   161  
   162  func (n *Name) Linksym() *obj.LSym               { return n.sym.Linksym() }
   163  func (n *Name) LinksymABI(abi obj.ABI) *obj.LSym { return n.sym.LinksymABI(abi) }
   164  
   165  func (*Name) CanBeNtype()    {}
   166  func (*Name) CanBeAnSSASym() {}
   167  func (*Name) CanBeAnSSAAux() {}
   168  
   169  // Pragma returns the PragmaFlag for p, which must be for an OTYPE.
   170  func (n *Name) Pragma() PragmaFlag { return n.pragma }
   171  
   172  // SetPragma sets the PragmaFlag for p, which must be for an OTYPE.
   173  func (n *Name) SetPragma(flag PragmaFlag) { n.pragma = flag }
   174  
   175  // Alias reports whether p, which must be for an OTYPE, is a type alias.
   176  func (n *Name) Alias() bool { return n.flags&nameAlias != 0 }
   177  
   178  // SetAlias sets whether p, which must be for an OTYPE, is a type alias.
   179  func (n *Name) SetAlias(alias bool) { n.flags.set(nameAlias, alias) }
   180  
   181  const (
   182  	nameReadonly                 = 1 << iota
   183  	nameByval                    // is the variable captured by value or by reference
   184  	nameNeedzero                 // if it contains pointers, needs to be zeroed on function entry
   185  	nameAutoTemp                 // is the variable a temporary (implies no dwarf info. reset if escapes to heap)
   186  	nameUsed                     // for variable declared and not used error
   187  	nameIsClosureVar             // PAUTOHEAP closure pseudo-variable; original (if any) at n.Defn
   188  	nameIsOutputParamHeapAddr    // pointer to a result parameter's heap copy
   189  	nameIsOutputParamInRegisters // output parameter in registers spills as an auto
   190  	nameAddrtaken                // address taken, even if not moved to heap
   191  	nameInlFormal                // PAUTO created by inliner, derived from callee formal
   192  	nameInlLocal                 // PAUTO created by inliner, derived from callee local
   193  	nameOpenDeferSlot            // if temporary var storing info for open-coded defers
   194  	nameLibfuzzer8BitCounter     // if PEXTERN should be assigned to __sancov_cntrs section
   195  	nameCoverageAuxVar           // instrumentation counter var or pkg ID for cmd/cover
   196  	nameAlias                    // is type name an alias
   197  	nameNonMergeable             // not a candidate for stack slot merging
   198  )
   199  
   200  func (n *Name) Readonly() bool                 { return n.flags&nameReadonly != 0 }
   201  func (n *Name) Needzero() bool                 { return n.flags&nameNeedzero != 0 }
   202  func (n *Name) AutoTemp() bool                 { return n.flags&nameAutoTemp != 0 }
   203  func (n *Name) Used() bool                     { return n.flags&nameUsed != 0 }
   204  func (n *Name) IsClosureVar() bool             { return n.flags&nameIsClosureVar != 0 }
   205  func (n *Name) IsOutputParamHeapAddr() bool    { return n.flags&nameIsOutputParamHeapAddr != 0 }
   206  func (n *Name) IsOutputParamInRegisters() bool { return n.flags&nameIsOutputParamInRegisters != 0 }
   207  func (n *Name) Addrtaken() bool                { return n.flags&nameAddrtaken != 0 }
   208  func (n *Name) InlFormal() bool                { return n.flags&nameInlFormal != 0 }
   209  func (n *Name) InlLocal() bool                 { return n.flags&nameInlLocal != 0 }
   210  func (n *Name) OpenDeferSlot() bool            { return n.flags&nameOpenDeferSlot != 0 }
   211  func (n *Name) Libfuzzer8BitCounter() bool     { return n.flags&nameLibfuzzer8BitCounter != 0 }
   212  func (n *Name) CoverageAuxVar() bool           { return n.flags&nameCoverageAuxVar != 0 }
   213  func (n *Name) NonMergeable() bool             { return n.flags&nameNonMergeable != 0 }
   214  
   215  func (n *Name) setReadonly(b bool)                 { n.flags.set(nameReadonly, b) }
   216  func (n *Name) SetNeedzero(b bool)                 { n.flags.set(nameNeedzero, b) }
   217  func (n *Name) SetAutoTemp(b bool)                 { n.flags.set(nameAutoTemp, b) }
   218  func (n *Name) SetUsed(b bool)                     { n.flags.set(nameUsed, b) }
   219  func (n *Name) SetIsClosureVar(b bool)             { n.flags.set(nameIsClosureVar, b) }
   220  func (n *Name) SetIsOutputParamHeapAddr(b bool)    { n.flags.set(nameIsOutputParamHeapAddr, b) }
   221  func (n *Name) SetIsOutputParamInRegisters(b bool) { n.flags.set(nameIsOutputParamInRegisters, b) }
   222  func (n *Name) SetAddrtaken(b bool)                { n.flags.set(nameAddrtaken, b) }
   223  func (n *Name) SetInlFormal(b bool)                { n.flags.set(nameInlFormal, b) }
   224  func (n *Name) SetInlLocal(b bool)                 { n.flags.set(nameInlLocal, b) }
   225  func (n *Name) SetOpenDeferSlot(b bool)            { n.flags.set(nameOpenDeferSlot, b) }
   226  func (n *Name) SetLibfuzzer8BitCounter(b bool)     { n.flags.set(nameLibfuzzer8BitCounter, b) }
   227  func (n *Name) SetCoverageAuxVar(b bool)           { n.flags.set(nameCoverageAuxVar, b) }
   228  func (n *Name) SetNonMergeable(b bool)             { n.flags.set(nameNonMergeable, b) }
   229  
   230  // OnStack reports whether variable n may reside on the stack.
   231  func (n *Name) OnStack() bool {
   232  	if n.Op() == ONAME {
   233  		switch n.Class {
   234  		case PPARAM, PPARAMOUT, PAUTO:
   235  			return n.Esc() != EscHeap
   236  		case PEXTERN, PAUTOHEAP:
   237  			return false
   238  		}
   239  	}
   240  	// Note: fmt.go:dumpNodeHeader calls all "func() bool"-typed
   241  	// methods, but it can only recover from panics, not Fatalf.
   242  	panic(fmt.Sprintf("%v: not a variable: %v", base.FmtPos(n.Pos()), n))
   243  }
   244  
   245  // MarkReadonly indicates that n is an ONAME with readonly contents.
   246  func (n *Name) MarkReadonly() {
   247  	if n.Op() != ONAME {
   248  		base.Fatalf("Node.MarkReadonly %v", n.Op())
   249  	}
   250  	n.setReadonly(true)
   251  	// Mark the linksym as readonly immediately
   252  	// so that the SSA backend can use this information.
   253  	// It will be overridden later during dumpglobls.
   254  	n.Linksym().Type = objabi.SRODATA
   255  }
   256  
   257  // Val returns the constant.Value for the node.
   258  func (n *Name) Val() constant.Value {
   259  	if n.val == nil {
   260  		return constant.MakeUnknown()
   261  	}
   262  	return n.val
   263  }
   264  
   265  // SetVal sets the constant.Value for the node.
   266  func (n *Name) SetVal(v constant.Value) {
   267  	if n.op != OLITERAL {
   268  		panic(n.no("SetVal"))
   269  	}
   270  	AssertValidTypeForConst(n.Type(), v)
   271  	n.val = v
   272  }
   273  
   274  // Canonical returns the logical declaration that n represents. If n
   275  // is a closure variable, then Canonical returns the original Name as
   276  // it appears in the function that immediately contains the
   277  // declaration. Otherwise, Canonical simply returns n itself.
   278  func (n *Name) Canonical() *Name {
   279  	if n.IsClosureVar() && n.Defn != nil {
   280  		n = n.Defn.(*Name)
   281  	}
   282  	return n
   283  }
   284  
   285  func (n *Name) SetByval(b bool) {
   286  	if n.Canonical() != n {
   287  		base.Fatalf("SetByval called on non-canonical variable: %v", n)
   288  	}
   289  	n.flags.set(nameByval, b)
   290  }
   291  
   292  func (n *Name) Byval() bool {
   293  	// We require byval to be set on the canonical variable, but we
   294  	// allow it to be accessed from any instance.
   295  	return n.Canonical().flags&nameByval != 0
   296  }
   297  
   298  // NewClosureVar returns a new closure variable for fn to refer to
   299  // outer variable n.
   300  func NewClosureVar(pos src.XPos, fn *Func, n *Name) *Name {
   301  	switch n.Class {
   302  	case PAUTO, PPARAM, PPARAMOUT, PAUTOHEAP:
   303  		// ok
   304  	default:
   305  		// Prevent mistaken capture of global variables.
   306  		base.Fatalf("NewClosureVar: %+v", n)
   307  	}
   308  
   309  	c := NewNameAt(pos, n.Sym(), n.Type())
   310  	c.Curfn = fn
   311  	c.Class = PAUTOHEAP
   312  	c.SetIsClosureVar(true)
   313  	c.Defn = n.Canonical()
   314  	c.Outer = n
   315  
   316  	fn.ClosureVars = append(fn.ClosureVars, c)
   317  
   318  	return c
   319  }
   320  
   321  // NewHiddenParam returns a new hidden parameter for fn with the given
   322  // name and type.
   323  func NewHiddenParam(pos src.XPos, fn *Func, sym *types.Sym, typ *types.Type) *Name {
   324  	if fn.OClosure != nil {
   325  		base.FatalfAt(fn.Pos(), "cannot add hidden parameters to closures")
   326  	}
   327  
   328  	fn.SetNeedctxt(true)
   329  
   330  	// Create a fake parameter, disassociated from any real function, to
   331  	// pretend to capture.
   332  	fake := NewNameAt(pos, sym, typ)
   333  	fake.Class = PPARAM
   334  	fake.SetByval(true)
   335  
   336  	return NewClosureVar(pos, fn, fake)
   337  }
   338  
   339  // SameSource reports whether two nodes refer to the same source
   340  // element.
   341  //
   342  // It exists to help incrementally migrate the compiler towards
   343  // allowing the introduction of IdentExpr (#42990). Once we have
   344  // IdentExpr, it will no longer be safe to directly compare Node
   345  // values to tell if they refer to the same Name. Instead, code will
   346  // need to explicitly get references to the underlying Name object(s),
   347  // and compare those instead.
   348  //
   349  // It will still be safe to compare Nodes directly for checking if two
   350  // nodes are syntactically the same. The SameSource function exists to
   351  // indicate code that intentionally compares Nodes for syntactic
   352  // equality as opposed to code that has yet to be updated in
   353  // preparation for IdentExpr.
   354  func SameSource(n1, n2 Node) bool {
   355  	return n1 == n2
   356  }
   357  
   358  // Uses reports whether expression x is a (direct) use of the given
   359  // variable.
   360  func Uses(x Node, v *Name) bool {
   361  	if v == nil || v.Op() != ONAME {
   362  		base.Fatalf("RefersTo bad Name: %v", v)
   363  	}
   364  	return x.Op() == ONAME && x.Name() == v
   365  }
   366  
   367  // DeclaredBy reports whether expression x refers (directly) to a
   368  // variable that was declared by the given statement.
   369  func DeclaredBy(x, stmt Node) bool {
   370  	if stmt == nil {
   371  		base.Fatalf("DeclaredBy nil")
   372  	}
   373  	return x.Op() == ONAME && SameSource(x.Name().Defn, stmt)
   374  }
   375  
   376  // The Class of a variable/function describes the "storage class"
   377  // of a variable or function. During parsing, storage classes are
   378  // called declaration contexts.
   379  type Class uint8
   380  
   381  //go:generate stringer -type=Class name.go
   382  const (
   383  	Pxxx       Class = iota // no class; used during ssa conversion to indicate pseudo-variables
   384  	PEXTERN                 // global variables
   385  	PAUTO                   // local variables
   386  	PAUTOHEAP               // local variables or parameters moved to heap
   387  	PPARAM                  // input arguments
   388  	PPARAMOUT               // output results
   389  	PTYPEPARAM              // type params
   390  	PFUNC                   // global functions
   391  
   392  	// Careful: Class is stored in three bits in Node.flags.
   393  	_ = uint((1 << 3) - iota) // static assert for iota <= (1 << 3)
   394  )
   395  
   396  type Embed struct {
   397  	Pos      src.XPos
   398  	Patterns []string
   399  }
   400
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