src/cmd/compile/internal/types2/const.go

// Copyright 2023 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.

// This file implements functions for untyped constant operands.

package types2

import (
	"cmd/compile/internal/syntax"
	"go/constant"
	"go/token"
	. "internal/types/errors"
	"math"
)

// overflow checks that the constant x is representable by its type.
// For untyped constants, it checks that the value doesn't become
// arbitrarily large.
func (check *Checker) overflow(x *operand, opPos syntax.Pos) {
	assert(x.mode == constant_)

	if x.val.Kind() == constant.Unknown {
		// TODO(gri) We should report exactly what went wrong. At the
		//           moment we don't have the (go/constant) API for that.
		//           See also TODO in go/constant/value.go.
		check.error(atPos(opPos), InvalidConstVal, "constant result is not representable")
		return
	}

	// Typed constants must be representable in
	// their type after each constant operation.
	// x.typ cannot be a type parameter (type
	// parameters cannot be constant types).
	if isTyped(x.typ) {
		check.representable(x, under(x.typ).(*Basic))
		return
	}

	// Untyped integer values must not grow arbitrarily.
	const prec = 512 // 512 is the constant precision
	if x.val.Kind() == constant.Int && constant.BitLen(x.val) > prec {
		op := opName(x.expr)
		if op != "" {
			op += " "
		}
		check.errorf(atPos(opPos), InvalidConstVal, "constant %soverflow", op)
		x.val = constant.MakeUnknown()
	}
}

// representableConst reports whether x can be represented as
// value of the given basic type and for the configuration
// provided (only needed for int/uint sizes).
//
// If rounded != nil, *rounded is set to the rounded value of x for
// representable floating-point and complex values, and to an Int
// value for integer values; it is left alone otherwise.
// It is ok to provide the addressof the first argument for rounded.
//
// The check parameter may be nil if representableConst is invoked
// (indirectly) through an exported API call (AssignableTo, ConvertibleTo)
// because we don't need the Checker's config for those calls.
func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *constant.Value) bool {
	if x.Kind() == constant.Unknown {
		return true // avoid follow-up errors
	}

	var conf *Config
	if check != nil {
		conf = check.conf
	}

	sizeof := func(T Type) int64 {
		s := conf.sizeof(T)
		return s
	}

	switch {
	case isInteger(typ):
		x := constant.ToInt(x)
		if x.Kind() != constant.Int {
			return false
		}
		if rounded != nil {
			*rounded = x
		}
		if x, ok := constant.Int64Val(x); ok {
			switch typ.kind {
			case Int:
				var s = uint(sizeof(typ)) * 8
				return int64(-1)<<(s-1) <= x && x <= int64(1)<<(s-1)-1
			case Int8:
				const s = 8
				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
			case Int16:
				const s = 16
				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
			case Int32:
				const s = 32
				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
			case Int64, UntypedInt:
				return true
			case Uint, Uintptr:
				if s := uint(sizeof(typ)) * 8; s < 64 {
					return 0 <= x && x <= int64(1)<<s-1
				}
				return 0 <= x
			case Uint8:
				const s = 8
				return 0 <= x && x <= 1<<s-1
			case Uint16:
				const s = 16
				return 0 <= x && x <= 1<<s-1
			case Uint32:
				const s = 32
				return 0 <= x && x <= 1<<s-1
			case Uint64:
				return 0 <= x
			default:
				panic("unreachable")
			}
		}
		// x does not fit into int64
		switch n := constant.BitLen(x); typ.kind {
		case Uint, Uintptr:
			var s = uint(sizeof(typ)) * 8
			return constant.Sign(x) >= 0 && n <= int(s)
		case Uint64:
			return constant.Sign(x) >= 0 && n <= 64
		case UntypedInt:
			return true
		}

	case isFloat(typ):
		x := constant.ToFloat(x)
		if x.Kind() != constant.Float {
			return false
		}
		switch typ.kind {
		case Float32:
			if rounded == nil {
				return fitsFloat32(x)
			}
			r := roundFloat32(x)
			if r != nil {
				*rounded = r
				return true
			}
		case Float64:
			if rounded == nil {
				return fitsFloat64(x)
			}
			r := roundFloat64(x)
			if r != nil {
				*rounded = r
				return true
			}
		case UntypedFloat:
			return true
		default:
			panic("unreachable")
		}

	case isComplex(typ):
		x := constant.ToComplex(x)
		if x.Kind() != constant.Complex {
			return false
		}
		switch typ.kind {
		case Complex64:
			if rounded == nil {
				return fitsFloat32(constant.Real(x)) && fitsFloat32(constant.Imag(x))
			}
			re := roundFloat32(constant.Real(x))
			im := roundFloat32(constant.Imag(x))
			if re != nil && im != nil {
				*rounded = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
				return true
			}
		case Complex128:
			if rounded == nil {
				return fitsFloat64(constant.Real(x)) && fitsFloat64(constant.Imag(x))
			}
			re := roundFloat64(constant.Real(x))
			im := roundFloat64(constant.Imag(x))
			if re != nil && im != nil {
				*rounded = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
				return true
			}
		case UntypedComplex:
			return true
		default:
			panic("unreachable")
		}

	case isString(typ):
		return x.Kind() == constant.String

	case isBoolean(typ):
		return x.Kind() == constant.Bool
	}

	return false
}

func fitsFloat32(x constant.Value) bool {
	f32, _ := constant.Float32Val(x)
	f := float64(f32)
	return !math.IsInf(f, 0)
}

func roundFloat32(x constant.Value) constant.Value {
	f32, _ := constant.Float32Val(x)
	f := float64(f32)
	if !math.IsInf(f, 0) {
		return constant.MakeFloat64(f)
	}
	return nil
}

func fitsFloat64(x constant.Value) bool {
	f, _ := constant.Float64Val(x)
	return !math.IsInf(f, 0)
}

func roundFloat64(x constant.Value) constant.Value {
	f, _ := constant.Float64Val(x)
	if !math.IsInf(f, 0) {
		return constant.MakeFloat64(f)
	}
	return nil
}

// representable checks that a constant operand is representable in the given
// basic type.
func (check *Checker) representable(x *operand, typ *Basic) {
	v, code := check.representation(x, typ)
	if code != 0 {
		check.invalidConversion(code, x, typ)
		x.mode = invalid
		return
	}
	assert(v != nil)
	x.val = v
}

// representation returns the representation of the constant operand x as the
// basic type typ.
//
// If no such representation is possible, it returns a non-zero error code.
func (check *Checker) representation(x *operand, typ *Basic) (constant.Value, Code) {
	assert(x.mode == constant_)
	v := x.val
	if !representableConst(x.val, check, typ, &v) {
		if isNumeric(x.typ) && isNumeric(typ) {
			// numeric conversion : error msg
			//
			// integer -> integer : overflows
			// integer -> float   : overflows (actually not possible)
			// float   -> integer : truncated
			// float   -> float   : overflows
			//
			if !isInteger(x.typ) && isInteger(typ) {
				return nil, TruncatedFloat
			} else {
				return nil, NumericOverflow
			}
		}
		return nil, InvalidConstVal
	}
	return v, 0
}

func (check *Checker) invalidConversion(code Code, x *operand, target Type) {
	msg := "cannot convert %s to type %s"
	switch code {
	case TruncatedFloat:
		msg = "%s truncated to %s"
	case NumericOverflow:
		msg = "%s overflows %s"
	}
	check.errorf(x, code, msg, x, target)
}

// convertUntyped attempts to set the type of an untyped value to the target type.
func (check *Checker) convertUntyped(x *operand, target Type) {
	newType, val, code := check.implicitTypeAndValue(x, target)
	if code != 0 {
		t := target
		if !isTypeParam(target) {
			t = safeUnderlying(target)
		}
		check.invalidConversion(code, x, t)
		x.mode = invalid
		return
	}
	if val != nil {
		x.val = val
		check.updateExprVal(x.expr, val)
	}
	if newType != x.typ {
		x.typ = newType
		check.updateExprType(x.expr, newType, false)
	}
}