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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 ssa
// This file defines the Const SSA value type.
import (
"fmt"
exact "go/constant"
"go/token"
"go/types"
"strconv"
)
// 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 exact.Value, typ types.Type) *Const {
return &Const{typ, val}
}
// 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) *Const {
return NewConst(exact.MakeInt64(i), tInt)
}
// nilConst returns a nil constant of the specified type, which may
// be any reference type, including interfaces.
//
func nilConst(typ types.Type) *Const {
return NewConst(nil, typ)
}
// stringConst returns a 'string' constant that evaluates to s.
func stringConst(s string) *Const {
return NewConst(exact.MakeString(s), tString)
}
// zeroConst returns a new "zero" constant of the specified type,
// which must not be an array or struct type: the zero values of
// aggregates are well-defined but cannot be represented by Const.
//
func zeroConst(t types.Type) *Const {
switch t := t.(type) {
case *types.Basic:
switch {
case t.Info()&types.IsBoolean != 0:
return NewConst(exact.MakeBool(false), t)
case t.Info()&types.IsNumeric != 0:
return NewConst(exact.MakeInt64(0), t)
case t.Info()&types.IsString != 0:
return NewConst(exact.MakeString(""), t)
case t.Kind() == types.UnsafePointer:
fallthrough
case t.Kind() == types.UntypedNil:
return nilConst(t)
default:
panic(fmt.Sprint("zeroConst for unexpected type:", t))
}
case *types.Pointer, *types.Slice, *types.Interface, *types.Chan, *types.Map, *types.Signature:
return nilConst(t)
case *types.Named:
return NewConst(zeroConst(t.Underlying()).Value, t)
case *types.Array, *types.Struct, *types.Tuple:
panic(fmt.Sprint("zeroConst applied to aggregate:", t))
}
panic(fmt.Sprint("zeroConst: unexpected ", t))
}
func (c *Const) RelString(from *types.Package) string {
var s string
if c.Value == nil {
s = "nil"
} else if c.Value.Kind() == exact.String {
s = exact.StringVal(c.Value)
const max = 20
// TODO(adonovan): don't cut a rune in half.
if len(s) > max {
s = s[:max-3] + "..." // abbreviate
}
s = strconv.Quote(s)
} else {
s = c.Value.String()
}
return s + ":" + relType(c.Type(), from)
}
func (c *Const) Name() string {
return c.RelString(nil)
}
func (c *Const) String() string {
return c.Name()
}
func (c *Const) Type() types.Type {
return c.typ
}
func (c *Const) Referrers() *[]Instruction {
return nil
}
func (c *Const) Parent() *Function { return nil }
func (c *Const) Pos() token.Pos {
return token.NoPos
}
// IsNil returns true if this constant represents a typed or untyped nil value.
func (c *Const) IsNil() bool {
return c.Value == nil
}
// TODO(adonovan): move everything below into golang.org/x/tools/go/ssa/interp.
// Int64 returns the numeric value of this constant truncated to fit
// a signed 64-bit integer.
//
func (c *Const) Int64() int64 {
switch x := exact.ToInt(c.Value); x.Kind() {
case exact.Int:
if i, ok := exact.Int64Val(x); ok {
return i
}
return 0
case exact.Float:
f, _ := exact.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 := exact.ToInt(c.Value); x.Kind() {
case exact.Int:
if u, ok := exact.Uint64Val(x); ok {
return u
}
return 0
case exact.Float:
f, _ := exact.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 {
f, _ := exact.Float64Val(c.Value)
return f
}
// Complex128 returns the complex value of this constant truncated to
// fit a complex128.
//
func (c *Const) Complex128() complex128 {
re, _ := exact.Float64Val(exact.Real(c.Value))
im, _ := exact.Float64Val(exact.Imag(c.Value))
return complex(re, im)
}