value.go

     1  // Copyright 2015 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 ssa
     6  
     7  import (
     8  	"cmd/compile/internal/ir"
     9  	"cmd/compile/internal/types"
    10  	"cmd/internal/src"
    11  	"fmt"
    12  	"math"
    13  	"sort"
    14  	"strings"
    15  )
    16  
    17  // A Value represents a value in the SSA representation of the program.
    18  // The ID and Type fields must not be modified. The remainder may be modified
    19  // if they preserve the value of the Value (e.g. changing a (mul 2 x) to an (add x x)).
    20  type Value struct {
    21  	// A unique identifier for the value. For performance we allocate these IDs
    22  	// densely starting at 1.  There is no guarantee that there won't be occasional holes, though.
    23  	ID ID
    24  
    25  	// The operation that computes this value. See op.go.
    26  	Op Op
    27  
    28  	// The type of this value. Normally this will be a Go type, but there
    29  	// are a few other pseudo-types, see ../types/type.go.
    30  	Type *types.Type
    31  
    32  	// Auxiliary info for this value. The type of this information depends on the opcode and type.
    33  	// AuxInt is used for integer values, Aux is used for other values.
    34  	// Floats are stored in AuxInt using math.Float64bits(f).
    35  	// Unused portions of AuxInt are filled by sign-extending the used portion,
    36  	// even if the represented value is unsigned.
    37  	// Users of AuxInt which interpret AuxInt as unsigned (e.g. shifts) must be careful.
    38  	// Use Value.AuxUnsigned to get the zero-extended value of AuxInt.
    39  	AuxInt int64
    40  	Aux    Aux
    41  
    42  	// Arguments of this value
    43  	Args []*Value
    44  
    45  	// Containing basic block
    46  	Block *Block
    47  
    48  	// Source position
    49  	Pos src.XPos
    50  
    51  	// Use count. Each appearance in Value.Args and Block.Controls counts once.
    52  	Uses int32
    53  
    54  	// wasm: Value stays on the WebAssembly stack. This value will not get a "register" (WebAssembly variable)
    55  	// nor a slot on Go stack, and the generation of this value is delayed to its use time.
    56  	OnWasmStack bool
    57  
    58  	// Is this value in the per-function constant cache? If so, remove from cache before changing it or recycling it.
    59  	InCache bool
    60  
    61  	// Storage for the first three args
    62  	argstorage [3]*Value
    63  }
    64  
    65  // Examples:
    66  // Opcode          aux   args
    67  //  OpAdd          nil      2
    68  //  OpConst     string      0    string constant
    69  //  OpConst      int64      0    int64 constant
    70  //  OpAddcq      int64      1    amd64 op: v = arg[0] + constant
    71  
    72  // short form print. Just v#.
    73  func (v *Value) String() string {
    74  	if v == nil {
    75  		return "nil" // should never happen, but not panicking helps with debugging
    76  	}
    77  	return fmt.Sprintf("v%d", v.ID)
    78  }
    79  
    80  func (v *Value) AuxInt8() int8 {
    81  	if opcodeTable[v.Op].auxType != auxInt8 && opcodeTable[v.Op].auxType != auxNameOffsetInt8 {
    82  		v.Fatalf("op %s doesn't have an int8 aux field", v.Op)
    83  	}
    84  	return int8(v.AuxInt)
    85  }
    86  
    87  func (v *Value) AuxInt16() int16 {
    88  	if opcodeTable[v.Op].auxType != auxInt16 {
    89  		v.Fatalf("op %s doesn't have an int16 aux field", v.Op)
    90  	}
    91  	return int16(v.AuxInt)
    92  }
    93  
    94  func (v *Value) AuxInt32() int32 {
    95  	if opcodeTable[v.Op].auxType != auxInt32 {
    96  		v.Fatalf("op %s doesn't have an int32 aux field", v.Op)
    97  	}
    98  	return int32(v.AuxInt)
    99  }
   100  
   101  // AuxUnsigned returns v.AuxInt as an unsigned value for OpConst*.
   102  // v.AuxInt is always sign-extended to 64 bits, even if the
   103  // represented value is unsigned. This undoes that sign extension.
   104  func (v *Value) AuxUnsigned() uint64 {
   105  	c := v.AuxInt
   106  	switch v.Op {
   107  	case OpConst64:
   108  		return uint64(c)
   109  	case OpConst32:
   110  		return uint64(uint32(c))
   111  	case OpConst16:
   112  		return uint64(uint16(c))
   113  	case OpConst8:
   114  		return uint64(uint8(c))
   115  	}
   116  	v.Fatalf("op %s isn't OpConst*", v.Op)
   117  	return 0
   118  }
   119  
   120  func (v *Value) AuxFloat() float64 {
   121  	if opcodeTable[v.Op].auxType != auxFloat32 && opcodeTable[v.Op].auxType != auxFloat64 {
   122  		v.Fatalf("op %s doesn't have a float aux field", v.Op)
   123  	}
   124  	return math.Float64frombits(uint64(v.AuxInt))
   125  }
   126  func (v *Value) AuxValAndOff() ValAndOff {
   127  	if opcodeTable[v.Op].auxType != auxSymValAndOff {
   128  		v.Fatalf("op %s doesn't have a ValAndOff aux field", v.Op)
   129  	}
   130  	return ValAndOff(v.AuxInt)
   131  }
   132  
   133  func (v *Value) AuxArm64BitField() arm64BitField {
   134  	if opcodeTable[v.Op].auxType != auxARM64BitField {
   135  		v.Fatalf("op %s doesn't have a ValAndOff aux field", v.Op)
   136  	}
   137  	return arm64BitField(v.AuxInt)
   138  }
   139  
   140  // long form print.  v# = opcode <type> [aux] args [: reg] (names)
   141  func (v *Value) LongString() string {
   142  	if v == nil {
   143  		return "<NIL VALUE>"
   144  	}
   145  	s := fmt.Sprintf("v%d = %s", v.ID, v.Op)
   146  	s += " <" + v.Type.String() + ">"
   147  	s += v.auxString()
   148  	for _, a := range v.Args {
   149  		s += fmt.Sprintf(" %v", a)
   150  	}
   151  	var r []Location
   152  	if v.Block != nil {
   153  		r = v.Block.Func.RegAlloc
   154  	}
   155  	if int(v.ID) < len(r) && r[v.ID] != nil {
   156  		s += " : " + r[v.ID].String()
   157  	}
   158  	var names []string
   159  	if v.Block != nil {
   160  		for name, values := range v.Block.Func.NamedValues {
   161  			for _, value := range values {
   162  				if value == v {
   163  					names = append(names, name.String())
   164  					break // drop duplicates.
   165  				}
   166  			}
   167  		}
   168  	}
   169  	if len(names) != 0 {
   170  		sort.Strings(names) // Otherwise a source of variation in debugging output.
   171  		s += " (" + strings.Join(names, ", ") + ")"
   172  	}
   173  	return s
   174  }
   175  
   176  func (v *Value) auxString() string {
   177  	switch opcodeTable[v.Op].auxType {
   178  	case auxBool:
   179  		if v.AuxInt == 0 {
   180  			return " [false]"
   181  		} else {
   182  			return " [true]"
   183  		}
   184  	case auxInt8:
   185  		return fmt.Sprintf(" [%d]", v.AuxInt8())
   186  	case auxInt16:
   187  		return fmt.Sprintf(" [%d]", v.AuxInt16())
   188  	case auxInt32:
   189  		return fmt.Sprintf(" [%d]", v.AuxInt32())
   190  	case auxInt64, auxInt128:
   191  		return fmt.Sprintf(" [%d]", v.AuxInt)
   192  	case auxARM64BitField:
   193  		lsb := v.AuxArm64BitField().getARM64BFlsb()
   194  		width := v.AuxArm64BitField().getARM64BFwidth()
   195  		return fmt.Sprintf(" [lsb=%d,width=%d]", lsb, width)
   196  	case auxFloat32, auxFloat64:
   197  		return fmt.Sprintf(" [%g]", v.AuxFloat())
   198  	case auxString:
   199  		return fmt.Sprintf(" {%q}", v.Aux)
   200  	case auxSym, auxCall, auxTyp:
   201  		if v.Aux != nil {
   202  			return fmt.Sprintf(" {%v}", v.Aux)
   203  		}
   204  	case auxSymOff, auxCallOff, auxTypSize, auxNameOffsetInt8:
   205  		s := ""
   206  		if v.Aux != nil {
   207  			s = fmt.Sprintf(" {%v}", v.Aux)
   208  		}
   209  		if v.AuxInt != 0 || opcodeTable[v.Op].auxType == auxNameOffsetInt8 {
   210  			s += fmt.Sprintf(" [%v]", v.AuxInt)
   211  		}
   212  		return s
   213  	case auxSymValAndOff:
   214  		s := ""
   215  		if v.Aux != nil {
   216  			s = fmt.Sprintf(" {%v}", v.Aux)
   217  		}
   218  		return s + fmt.Sprintf(" [%s]", v.AuxValAndOff())
   219  	case auxCCop:
   220  		return fmt.Sprintf(" {%s}", Op(v.AuxInt))
   221  	case auxS390XCCMask, auxS390XRotateParams:
   222  		return fmt.Sprintf(" {%v}", v.Aux)
   223  	case auxFlagConstant:
   224  		return fmt.Sprintf("[%s]", flagConstant(v.AuxInt))
   225  	}
   226  	return ""
   227  }
   228  
   229  // If/when midstack inlining is enabled (-l=4), the compiler gets both larger and slower.
   230  // Not-inlining this method is a help (*Value.reset and *Block.NewValue0 are similar).
   231  //go:noinline
   232  func (v *Value) AddArg(w *Value) {
   233  	if v.Args == nil {
   234  		v.resetArgs() // use argstorage
   235  	}
   236  	v.Args = append(v.Args, w)
   237  	w.Uses++
   238  }
   239  
   240  //go:noinline
   241  func (v *Value) AddArg2(w1, w2 *Value) {
   242  	if v.Args == nil {
   243  		v.resetArgs() // use argstorage
   244  	}
   245  	v.Args = append(v.Args, w1, w2)
   246  	w1.Uses++
   247  	w2.Uses++
   248  }
   249  
   250  //go:noinline
   251  func (v *Value) AddArg3(w1, w2, w3 *Value) {
   252  	if v.Args == nil {
   253  		v.resetArgs() // use argstorage
   254  	}
   255  	v.Args = append(v.Args, w1, w2, w3)
   256  	w1.Uses++
   257  	w2.Uses++
   258  	w3.Uses++
   259  }
   260  
   261  //go:noinline
   262  func (v *Value) AddArg4(w1, w2, w3, w4 *Value) {
   263  	v.Args = append(v.Args, w1, w2, w3, w4)
   264  	w1.Uses++
   265  	w2.Uses++
   266  	w3.Uses++
   267  	w4.Uses++
   268  }
   269  
   270  //go:noinline
   271  func (v *Value) AddArg5(w1, w2, w3, w4, w5 *Value) {
   272  	v.Args = append(v.Args, w1, w2, w3, w4, w5)
   273  	w1.Uses++
   274  	w2.Uses++
   275  	w3.Uses++
   276  	w4.Uses++
   277  	w5.Uses++
   278  }
   279  
   280  //go:noinline
   281  func (v *Value) AddArg6(w1, w2, w3, w4, w5, w6 *Value) {
   282  	v.Args = append(v.Args, w1, w2, w3, w4, w5, w6)
   283  	w1.Uses++
   284  	w2.Uses++
   285  	w3.Uses++
   286  	w4.Uses++
   287  	w5.Uses++
   288  	w6.Uses++
   289  }
   290  
   291  func (v *Value) AddArgs(a ...*Value) {
   292  	if v.Args == nil {
   293  		v.resetArgs() // use argstorage
   294  	}
   295  	v.Args = append(v.Args, a...)
   296  	for _, x := range a {
   297  		x.Uses++
   298  	}
   299  }
   300  func (v *Value) SetArg(i int, w *Value) {
   301  	v.Args[i].Uses--
   302  	v.Args[i] = w
   303  	w.Uses++
   304  }
   305  func (v *Value) SetArgs1(a *Value) {
   306  	v.resetArgs()
   307  	v.AddArg(a)
   308  }
   309  func (v *Value) SetArgs2(a, b *Value) {
   310  	v.resetArgs()
   311  	v.AddArg(a)
   312  	v.AddArg(b)
   313  }
   314  func (v *Value) SetArgs3(a, b, c *Value) {
   315  	v.resetArgs()
   316  	v.AddArg(a)
   317  	v.AddArg(b)
   318  	v.AddArg(c)
   319  }
   320  
   321  func (v *Value) resetArgs() {
   322  	for _, a := range v.Args {
   323  		a.Uses--
   324  	}
   325  	v.argstorage[0] = nil
   326  	v.argstorage[1] = nil
   327  	v.argstorage[2] = nil
   328  	v.Args = v.argstorage[:0]
   329  }
   330  
   331  // reset is called from most rewrite rules.
   332  // Allowing it to be inlined increases the size
   333  // of cmd/compile by almost 10%, and slows it down.
   334  //go:noinline
   335  func (v *Value) reset(op Op) {
   336  	if v.InCache {
   337  		v.Block.Func.unCache(v)
   338  	}
   339  	v.Op = op
   340  	v.resetArgs()
   341  	v.AuxInt = 0
   342  	v.Aux = nil
   343  }
   344  
   345  // invalidateRecursively marks a value as invalid (unused)
   346  // and after decrementing reference counts on its Args,
   347  // also recursively invalidates any of those whose use
   348  // count goes to zero.  It returns whether any of the
   349  // invalidated values was marked with IsStmt.
   350  //
   351  // BEWARE of doing this *before* you've applied intended
   352  // updates to SSA.
   353  func (v *Value) invalidateRecursively() bool {
   354  	lostStmt := v.Pos.IsStmt() == src.PosIsStmt
   355  	if v.InCache {
   356  		v.Block.Func.unCache(v)
   357  	}
   358  	v.Op = OpInvalid
   359  
   360  	for _, a := range v.Args {
   361  		a.Uses--
   362  		if a.Uses == 0 {
   363  			lost := a.invalidateRecursively()
   364  			lostStmt = lost || lostStmt
   365  		}
   366  	}
   367  
   368  	v.argstorage[0] = nil
   369  	v.argstorage[1] = nil
   370  	v.argstorage[2] = nil
   371  	v.Args = v.argstorage[:0]
   372  
   373  	v.AuxInt = 0
   374  	v.Aux = nil
   375  	return lostStmt
   376  }
   377  
   378  // copyOf is called from rewrite rules.
   379  // It modifies v to be (Copy a).
   380  //go:noinline
   381  func (v *Value) copyOf(a *Value) {
   382  	if v == a {
   383  		return
   384  	}
   385  	if v.InCache {
   386  		v.Block.Func.unCache(v)
   387  	}
   388  	v.Op = OpCopy
   389  	v.resetArgs()
   390  	v.AddArg(a)
   391  	v.AuxInt = 0
   392  	v.Aux = nil
   393  	v.Type = a.Type
   394  }
   395  
   396  // copyInto makes a new value identical to v and adds it to the end of b.
   397  // unlike copyIntoWithXPos this does not check for v.Pos being a statement.
   398  func (v *Value) copyInto(b *Block) *Value {
   399  	c := b.NewValue0(v.Pos.WithNotStmt(), v.Op, v.Type) // Lose the position, this causes line number churn otherwise.
   400  	c.Aux = v.Aux
   401  	c.AuxInt = v.AuxInt
   402  	c.AddArgs(v.Args...)
   403  	for _, a := range v.Args {
   404  		if a.Type.IsMemory() {
   405  			v.Fatalf("can't move a value with a memory arg %s", v.LongString())
   406  		}
   407  	}
   408  	return c
   409  }
   410  
   411  // copyIntoWithXPos makes a new value identical to v and adds it to the end of b.
   412  // The supplied position is used as the position of the new value.
   413  // Because this is used for rematerialization, check for case that (rematerialized)
   414  // input to value with position 'pos' carried a statement mark, and that the supplied
   415  // position (of the instruction using the rematerialized value) is not marked, and
   416  // preserve that mark if its line matches the supplied position.
   417  func (v *Value) copyIntoWithXPos(b *Block, pos src.XPos) *Value {
   418  	if v.Pos.IsStmt() == src.PosIsStmt && pos.IsStmt() != src.PosIsStmt && v.Pos.SameFileAndLine(pos) {
   419  		pos = pos.WithIsStmt()
   420  	}
   421  	c := b.NewValue0(pos, v.Op, v.Type)
   422  	c.Aux = v.Aux
   423  	c.AuxInt = v.AuxInt
   424  	c.AddArgs(v.Args...)
   425  	for _, a := range v.Args {
   426  		if a.Type.IsMemory() {
   427  			v.Fatalf("can't move a value with a memory arg %s", v.LongString())
   428  		}
   429  	}
   430  	return c
   431  }
   432  
   433  func (v *Value) Logf(msg string, args ...interface{}) { v.Block.Logf(msg, args...) }
   434  func (v *Value) Log() bool                            { return v.Block.Log() }
   435  func (v *Value) Fatalf(msg string, args ...interface{}) {
   436  	v.Block.Func.fe.Fatalf(v.Pos, msg, args...)
   437  }
   438  
   439  // isGenericIntConst reports whether v is a generic integer constant.
   440  func (v *Value) isGenericIntConst() bool {
   441  	return v != nil && (v.Op == OpConst64 || v.Op == OpConst32 || v.Op == OpConst16 || v.Op == OpConst8)
   442  }
   443  
   444  // ResultReg returns the result register assigned to v, in cmd/internal/obj/$ARCH numbering.
   445  // It is similar to Reg and Reg0, except that it is usable interchangeably for all Value Ops.
   446  // If you know v.Op, using Reg or Reg0 (as appropriate) will be more efficient.
   447  func (v *Value) ResultReg() int16 {
   448  	reg := v.Block.Func.RegAlloc[v.ID]
   449  	if reg == nil {
   450  		v.Fatalf("nil reg for value: %s\n%s\n", v.LongString(), v.Block.Func)
   451  	}
   452  	if pair, ok := reg.(LocPair); ok {
   453  		reg = pair[0]
   454  	}
   455  	if reg == nil {
   456  		v.Fatalf("nil reg0 for value: %s\n%s\n", v.LongString(), v.Block.Func)
   457  	}
   458  	return reg.(*Register).objNum
   459  }
   460  
   461  // Reg returns the register assigned to v, in cmd/internal/obj/$ARCH numbering.
   462  func (v *Value) Reg() int16 {
   463  	reg := v.Block.Func.RegAlloc[v.ID]
   464  	if reg == nil {
   465  		v.Fatalf("nil register for value: %s\n%s\n", v.LongString(), v.Block.Func)
   466  	}
   467  	return reg.(*Register).objNum
   468  }
   469  
   470  // Reg0 returns the register assigned to the first output of v, in cmd/internal/obj/$ARCH numbering.
   471  func (v *Value) Reg0() int16 {
   472  	reg := v.Block.Func.RegAlloc[v.ID].(LocPair)[0]
   473  	if reg == nil {
   474  		v.Fatalf("nil first register for value: %s\n%s\n", v.LongString(), v.Block.Func)
   475  	}
   476  	return reg.(*Register).objNum
   477  }
   478  
   479  // Reg1 returns the register assigned to the second output of v, in cmd/internal/obj/$ARCH numbering.
   480  func (v *Value) Reg1() int16 {
   481  	reg := v.Block.Func.RegAlloc[v.ID].(LocPair)[1]
   482  	if reg == nil {
   483  		v.Fatalf("nil second register for value: %s\n%s\n", v.LongString(), v.Block.Func)
   484  	}
   485  	return reg.(*Register).objNum
   486  }
   487  
   488  func (v *Value) RegName() string {
   489  	reg := v.Block.Func.RegAlloc[v.ID]
   490  	if reg == nil {
   491  		v.Fatalf("nil register for value: %s\n%s\n", v.LongString(), v.Block.Func)
   492  	}
   493  	return reg.(*Register).name
   494  }
   495  
   496  // MemoryArg returns the memory argument for the Value.
   497  // The returned value, if non-nil, will be memory-typed (or a tuple with a memory-typed second part).
   498  // Otherwise, nil is returned.
   499  func (v *Value) MemoryArg() *Value {
   500  	if v.Op == OpPhi {
   501  		v.Fatalf("MemoryArg on Phi")
   502  	}
   503  	na := len(v.Args)
   504  	if na == 0 {
   505  		return nil
   506  	}
   507  	if m := v.Args[na-1]; m.Type.IsMemory() {
   508  		return m
   509  	}
   510  	return nil
   511  }
   512  
   513  // LackingPos indicates whether v is a value that is unlikely to have a correct
   514  // position assigned to it.  Ignoring such values leads to more user-friendly positions
   515  // assigned to nearby values and the blocks containing them.
   516  func (v *Value) LackingPos() bool {
   517  	// The exact definition of LackingPos is somewhat heuristically defined and may change
   518  	// in the future, for example if some of these operations are generated more carefully
   519  	// with respect to their source position.
   520  	return v.Op == OpVarDef || v.Op == OpVarKill || v.Op == OpVarLive || v.Op == OpPhi ||
   521  		(v.Op == OpFwdRef || v.Op == OpCopy) && v.Type == types.TypeMem
   522  }
   523  
   524  // removeable reports whether the value v can be removed from the SSA graph entirely
   525  // if its use count drops to 0.
   526  func (v *Value) removeable() bool {
   527  	if v.Type.IsVoid() {
   528  		// Void ops, like nil pointer checks, must stay.
   529  		return false
   530  	}
   531  	if v.Type.IsMemory() {
   532  		// We don't need to preserve all memory ops, but we do need
   533  		// to keep calls at least (because they might have
   534  		// synchronization operations we can't see).
   535  		return false
   536  	}
   537  	if v.Op.HasSideEffects() {
   538  		// These are mostly synchronization operations.
   539  		return false
   540  	}
   541  	return true
   542  }
   543  
   544  // TODO(mdempsky): Shouldn't be necessary; see discussion at golang.org/cl/275756
   545  func (*Value) CanBeAnSSAAux() {}
   546  
   547  // AutoVar returns a *Name and int64 representing the auto variable and offset within it
   548  // where v should be spilled.
   549  func AutoVar(v *Value) (*ir.Name, int64) {
   550  	if loc, ok := v.Block.Func.RegAlloc[v.ID].(LocalSlot); ok {
   551  		if v.Type.Size() > loc.Type.Size() {
   552  			v.Fatalf("spill/restore type %s doesn't fit in slot type %s", v.Type, loc.Type)
   553  		}
   554  		return loc.N, loc.Off
   555  	}
   556  	// Assume it is a register, return its spill slot, which needs to be live
   557  	nameOff := v.Aux.(*AuxNameOffset)
   558  	return nameOff.Name, nameOff.Offset
   559  }
   560
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