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243 lines (214 loc) · 6.17 KB
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// 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 file defines the Const SSA value type.
import (
"bytes"
"fmt"
"go/ast"
"go/constant"
"go/types"
"strconv"
"golang.org/x/exp/typeparams"
"honnef.co/go/tools/internal/xtools-internal/typesinternal"
)
// soleTypeKind returns a BasicInfo for which constant.Value can
// represent all zero values for the types in the type set.
//
// types.IsBoolean for false is a representative.
// types.IsInteger for 0
// types.IsString for ""
// 0 otherwise.
func soleTypeKind(typ types.Type) types.BasicInfo {
// State records the set of possible zero values (false, 0, "").
// Candidates (perhaps all) are eliminated during the type-set
// iteration, which executes at least once.
state := types.IsBoolean | types.IsInteger | types.IsString
underIs(typ, func(ut types.Type) bool {
var c types.BasicInfo
if t, ok := ut.(*types.Basic); ok {
c = t.Info()
}
if c&types.IsNumeric != 0 { // int/float/complex
c = types.IsInteger
}
state = state & c
return state != 0
})
return state
}
// NewConst returns a new constant of the specified value and type.
// val must be valid according to the specification of Const.Value.
func NewConst(val constant.Value, typ types.Type, source ast.Node) *Const {
if val == nil {
switch soleTypeKind(typ) {
case types.IsBoolean:
val = constant.MakeBool(false)
case types.IsInteger:
val = constant.MakeInt64(0)
case types.IsString:
val = constant.MakeString("")
}
}
c := &Const{
typ: typ,
Value: val,
}
c.setSource(source)
return c
}
// intConst returns an 'int' constant that evaluates to i.
// (i is an int64 in case the host is narrower than the target.)
func intConst(i int64, source ast.Node) *Const {
return NewConst(constant.MakeInt64(i), tInt, source)
}
// nilConst returns a nil constant of the specified type, which may
// be any reference type, including interfaces.
func nilConst(typ types.Type, source ast.Node) *Const {
return NewConst(nil, typ, source)
}
// stringConst returns a 'string' constant that evaluates to s.
func stringConst(s string, source ast.Node) *Const {
return NewConst(constant.MakeString(s), tString, source)
}
// zeroConst returns a new "zero" constant of the specified type.
func zeroConst(t types.Type, source ast.Node) Constant {
return NewConst(nil, t, source)
}
func (c *Const) RelString(from *types.Package) string {
var p string
if c.Value == nil {
switch c.typ.(type) {
case *types.Array, *types.Struct:
p = "{}"
case *types.Alias:
switch c.typ.Underlying().(type) {
case *types.Array, *types.Struct:
p = "{}"
default:
p, _ = typesinternal.ZeroString(types.Unalias(c.typ), types.RelativeTo(from))
}
default:
p, _ = typesinternal.ZeroString(c.typ, types.RelativeTo(from))
}
} else if c.Value.Kind() == constant.String {
v := constant.StringVal(c.Value)
const max = 20
// TODO(adonovan): don't cut a rune in half.
if len(v) > max {
v = v[:max-3] + "..." // abbreviate
}
p = strconv.Quote(v)
} else {
p = c.Value.String()
}
return p + ":" + relType(c.Type(), from)
}
func (c *Const) Name() string {
return c.RelString(nil)
}
func (c *Const) String() string {
return c.RelString(nil)
}
func (c *Const) Type() types.Type {
return c.typ
}
func (c *Const) Referrers() *[]Instruction {
return nil
}
func (c *Const) Parent() *Function { return nil }
func (v *AggregateConst) RelString(pkg *types.Package) string {
var b bytes.Buffer
fmt.Fprint(&b, "const {")
for i, vv := range v.Values {
if i > 0 {
fmt.Fprint(&b, ", ")
}
fmt.Fprint(&b, relName(vv, v))
}
fmt.Fprint(&b, "}")
return b.String()
}
func (v *AggregateConst) Name() string {
return v.RelString(nil)
}
func (v *AggregateConst) String() string {
return v.RelString(nil)
}
func (v *AggregateConst) Type() types.Type {
return v.typ
}
func (v *AggregateConst) Referrers() *[]Instruction {
return nil
}
func (v *AggregateConst) Parent() *Function { return nil }
// IsNil returns true if this constant represents a typed or untyped nil value.
func (c *Const) IsNil() bool {
return c.Value == nil && nillable(c.typ)
}
// nillable reports whether *new(T) == nil is legal for type T.
func nillable(t types.Type) bool {
if typeparams.IsTypeParam(t) {
return underIs(t, func(u types.Type) bool {
// empty type set (u==nil) => any underlying types => not nillable
return u != nil && nillable(u)
})
}
switch t := t.Underlying().(type) {
case *types.Basic:
return t.Kind() == types.UnsafePointer
case *types.Pointer, *types.Slice, *types.Chan, *types.Map, *types.Signature:
return true
case *types.Interface:
return true // basic interface.
default:
return false
}
}
// TODO(adonovan): move everything below into honnef.co/go/tools/go/ir/interp.
// Int64 returns the numeric value of this constant truncated to fit
// a signed 64-bit integer.
func (c *Const) Int64() int64 {
switch x := constant.ToInt(c.Value); x.Kind() {
case constant.Int:
if i, ok := constant.Int64Val(x); ok {
return i
}
return 0
case constant.Float:
f, _ := constant.Float64Val(x)
return int64(f)
}
panic(fmt.Sprintf("unexpected constant value: %T", c.Value))
}
// Uint64 returns the numeric value of this constant truncated to fit
// an unsigned 64-bit integer.
func (c *Const) Uint64() uint64 {
switch x := constant.ToInt(c.Value); x.Kind() {
case constant.Int:
if u, ok := constant.Uint64Val(x); ok {
return u
}
return 0
case constant.Float:
f, _ := constant.Float64Val(x)
return uint64(f)
}
panic(fmt.Sprintf("unexpected constant value: %T", c.Value))
}
// Float64 returns the numeric value of this constant truncated to fit
// a float64.
func (c *Const) Float64() float64 {
x := constant.ToFloat(c.Value) // (c.Value == nil) => x.Kind() == Unknown
f, _ := constant.Float64Val(x)
return f
}
// Complex128 returns the complex value of this constant truncated to
// fit a complex128.
func (c *Const) Complex128() complex128 {
x := constant.ToComplex(c.Value) // (c.Value == nil) => x.Kind() == Unknown
re, _ := constant.Float64Val(constant.Real(x))
im, _ := constant.Float64Val(constant.Imag(x))
return complex(re, im)
}