| 1 | // Copyright 2013 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 | // This file defines the Const SSA value type. |
| 8 | |
| 9 | import ( |
| 10 | "fmt" |
| 11 | "go/constant" |
| 12 | "go/token" |
| 13 | "go/types" |
| 14 | "strconv" |
| 15 | "strings" |
| 16 | |
| 17 | "golang.org/x/tools/internal/typeparams" |
| 18 | ) |
| 19 | |
| 20 | // NewConst returns a new constant of the specified value and type. |
| 21 | // val must be valid according to the specification of Const.Value. |
| 22 | func NewConst(val constant.Value, typ types.Type) *Const { |
| 23 | if val == nil { |
| 24 | switch soleTypeKind(typ) { |
| 25 | case types.IsBoolean: |
| 26 | val = constant.MakeBool(false) |
| 27 | case types.IsInteger: |
| 28 | val = constant.MakeInt64(0) |
| 29 | case types.IsString: |
| 30 | val = constant.MakeString("") |
| 31 | } |
| 32 | } |
| 33 | return &Const{typ, val} |
| 34 | } |
| 35 | |
| 36 | // soleTypeKind returns a BasicInfo for which constant.Value can |
| 37 | // represent all zero values for the types in the type set. |
| 38 | // |
| 39 | // types.IsBoolean for false is a representative. |
| 40 | // types.IsInteger for 0 |
| 41 | // types.IsString for "" |
| 42 | // 0 otherwise. |
| 43 | func soleTypeKind(typ types.Type) types.BasicInfo { |
| 44 | // State records the set of possible zero values (false, 0, ""). |
| 45 | // Candidates (perhaps all) are eliminated during the type-set |
| 46 | // iteration, which executes at least once. |
| 47 | state := types.IsBoolean | types.IsInteger | types.IsString |
| 48 | underIs(typeSetOf(typ), func(t types.Type) bool { |
| 49 | var c types.BasicInfo |
| 50 | if t, ok := t.(*types.Basic); ok { |
| 51 | c = t.Info() |
| 52 | } |
| 53 | if c&types.IsNumeric != 0 { // int/float/complex |
| 54 | c = types.IsInteger |
| 55 | } |
| 56 | state = state & c |
| 57 | return state != 0 |
| 58 | }) |
| 59 | return state |
| 60 | } |
| 61 | |
| 62 | // intConst returns an 'int' constant that evaluates to i. |
| 63 | // (i is an int64 in case the host is narrower than the target.) |
| 64 | func intConst(i int64) *Const { |
| 65 | return NewConst(constant.MakeInt64(i), tInt) |
| 66 | } |
| 67 | |
| 68 | // stringConst returns a 'string' constant that evaluates to s. |
| 69 | func stringConst(s string) *Const { |
| 70 | return NewConst(constant.MakeString(s), tString) |
| 71 | } |
| 72 | |
| 73 | // zeroConst returns a new "zero" constant of the specified type. |
| 74 | func zeroConst(t types.Type) *Const { |
| 75 | return NewConst(nil, t) |
| 76 | } |
| 77 | |
| 78 | func (c *Const) RelString(from *types.Package) string { |
| 79 | var s string |
| 80 | if c.Value == nil { |
| 81 | s = zeroString(c.typ, from) |
| 82 | } else if c.Value.Kind() == constant.String { |
| 83 | s = constant.StringVal(c.Value) |
| 84 | const max = 20 |
| 85 | // TODO(adonovan): don't cut a rune in half. |
| 86 | if len(s) > max { |
| 87 | s = s[:max-3] + "..." // abbreviate |
| 88 | } |
| 89 | s = strconv.Quote(s) |
| 90 | } else { |
| 91 | s = c.Value.String() |
| 92 | } |
| 93 | return s + ":" + relType(c.Type(), from) |
| 94 | } |
| 95 | |
| 96 | // zeroString returns the string representation of the "zero" value of the type t. |
| 97 | func zeroString(t types.Type, from *types.Package) string { |
| 98 | switch t := t.(type) { |
| 99 | case *types.Basic: |
| 100 | switch { |
| 101 | case t.Info()&types.IsBoolean != 0: |
| 102 | return "false" |
| 103 | case t.Info()&types.IsNumeric != 0: |
| 104 | return "0" |
| 105 | case t.Info()&types.IsString != 0: |
| 106 | return `""` |
| 107 | case t.Kind() == types.UnsafePointer: |
| 108 | fallthrough |
| 109 | case t.Kind() == types.UntypedNil: |
| 110 | return "nil" |
| 111 | default: |
| 112 | panic(fmt.Sprint("zeroString for unexpected type:", t)) |
| 113 | } |
| 114 | case *types.Pointer, *types.Slice, *types.Interface, *types.Chan, *types.Map, *types.Signature: |
| 115 | return "nil" |
| 116 | case *types.Named: |
| 117 | return zeroString(t.Underlying(), from) |
| 118 | case *types.Array, *types.Struct: |
| 119 | return relType(t, from) + "{}" |
| 120 | case *types.Tuple: |
| 121 | // Tuples are not normal values. |
| 122 | // We are currently format as "(t[0], ..., t[n])". Could be something else. |
| 123 | components := make([]string, t.Len()) |
| 124 | for i := 0; i < t.Len(); i++ { |
| 125 | components[i] = zeroString(t.At(i).Type(), from) |
| 126 | } |
| 127 | return "(" + strings.Join(components, ", ") + ")" |
| 128 | case *typeparams.TypeParam: |
| 129 | return "*new(" + relType(t, from) + ")" |
| 130 | } |
| 131 | panic(fmt.Sprint("zeroString: unexpected ", t)) |
| 132 | } |
| 133 | |
| 134 | func (c *Const) Name() string { |
| 135 | return c.RelString(nil) |
| 136 | } |
| 137 | |
| 138 | func (c *Const) String() string { |
| 139 | return c.Name() |
| 140 | } |
| 141 | |
| 142 | func (c *Const) Type() types.Type { |
| 143 | return c.typ |
| 144 | } |
| 145 | |
| 146 | func (c *Const) Referrers() *[]Instruction { |
| 147 | return nil |
| 148 | } |
| 149 | |
| 150 | func (c *Const) Parent() *Function { return nil } |
| 151 | |
| 152 | func (c *Const) Pos() token.Pos { |
| 153 | return token.NoPos |
| 154 | } |
| 155 | |
| 156 | // IsNil returns true if this constant represents a typed or untyped nil value |
| 157 | // with an underlying reference type: pointer, slice, chan, map, function, or |
| 158 | // *basic* interface. |
| 159 | // |
| 160 | // Note: a type parameter whose underlying type is a basic interface is |
| 161 | // considered a reference type. |
| 162 | func (c *Const) IsNil() bool { |
| 163 | return c.Value == nil && nillable(c.typ) |
| 164 | } |
| 165 | |
| 166 | // nillable reports whether *new(T) == nil is legal for type T. |
| 167 | func nillable(t types.Type) bool { |
| 168 | switch t := t.Underlying().(type) { |
| 169 | case *types.Pointer, *types.Slice, *types.Chan, *types.Map, *types.Signature: |
| 170 | return true |
| 171 | case *types.Interface: |
| 172 | return typeSetOf(t).Len() == 0 // basic interface. |
| 173 | default: |
| 174 | return false |
| 175 | } |
| 176 | } |
| 177 | |
| 178 | // TODO(adonovan): move everything below into golang.org/x/tools/go/ssa/interp. |
| 179 | |
| 180 | // Int64 returns the numeric value of this constant truncated to fit |
| 181 | // a signed 64-bit integer. |
| 182 | func (c *Const) Int64() int64 { |
| 183 | switch x := constant.ToInt(c.Value); x.Kind() { |
| 184 | case constant.Int: |
| 185 | if i, ok := constant.Int64Val(x); ok { |
| 186 | return i |
| 187 | } |
| 188 | return 0 |
| 189 | case constant.Float: |
| 190 | f, _ := constant.Float64Val(x) |
| 191 | return int64(f) |
| 192 | } |
| 193 | panic(fmt.Sprintf("unexpected constant value: %T", c.Value)) |
| 194 | } |
| 195 | |
| 196 | // Uint64 returns the numeric value of this constant truncated to fit |
| 197 | // an unsigned 64-bit integer. |
| 198 | func (c *Const) Uint64() uint64 { |
| 199 | switch x := constant.ToInt(c.Value); x.Kind() { |
| 200 | case constant.Int: |
| 201 | if u, ok := constant.Uint64Val(x); ok { |
| 202 | return u |
| 203 | } |
| 204 | return 0 |
| 205 | case constant.Float: |
| 206 | f, _ := constant.Float64Val(x) |
| 207 | return uint64(f) |
| 208 | } |
| 209 | panic(fmt.Sprintf("unexpected constant value: %T", c.Value)) |
| 210 | } |
| 211 | |
| 212 | // Float64 returns the numeric value of this constant truncated to fit |
| 213 | // a float64. |
| 214 | func (c *Const) Float64() float64 { |
| 215 | x := constant.ToFloat(c.Value) // (c.Value == nil) => x.Kind() == Unknown |
| 216 | f, _ := constant.Float64Val(x) |
| 217 | return f |
| 218 | } |
| 219 | |
| 220 | // Complex128 returns the complex value of this constant truncated to |
| 221 | // fit a complex128. |
| 222 | func (c *Const) Complex128() complex128 { |
| 223 | x := constant.ToComplex(c.Value) // (c.Value == nil) => x.Kind() == Unknown |
| 224 | re, _ := constant.Float64Val(constant.Real(x)) |
| 225 | im, _ := constant.Float64Val(constant.Imag(x)) |
| 226 | return complex(re, im) |
| 227 | } |
| 228 |
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