[dev.typeparams] cmd/compile/internal/types2: use 512 bits as max. integer precision

This matches the compiler's existing limitations and thus ensures
that types2 reports the same errors for oversize integer constants.

Change-Id: I4fb7c83f3af69098d96f7b6c53dbe3eaf6ea9ee4
Reviewed-on: https://go-review.googlesource.com/c/go/+/288633
Trust: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: griesemer

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

@@ -449,7 +449,7 @@ func EvalConst(n ir.Node) ir.Node {
 		n := n.(*ir.BinaryExpr)
 		nl, nr := n.X, n.Y
 		if nl.Op() == ir.OLITERAL && nr.Op() == ir.OLITERAL {
-			// shiftBound from go/types; "so we can express smallestFloat64"
+			// shiftBound from go/types; "so we can express smallestFloat64" (see issue #44057)
 			const shiftBound = 1023 - 1 + 52
 			s, ok := constant.Uint64Val(nr.Val())
 			if !ok || s > shiftBound {

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

@@ -96,9 +96,7 @@ func (check *Checker) overflow(x *operand) {
 	what := "" // operator description, if any
 	if op, _ := x.expr.(*syntax.Operation); op != nil {
 		pos = op.Pos()
-		if int(op.Op) < len(op2str) {
-			what = op2str[op.Op]
-		}
+		what = opName(op)
 	}
 
 	if x.val.Kind() == constant.Unknown {
@@ -117,15 +115,37 @@ func (check *Checker) overflow(x *operand) {
 	}
 
 	// Untyped integer values must not grow arbitrarily.
-	const limit = 4 * 512 // 512 is the constant precision - we need more because old tests had no limits
-	if x.val.Kind() == constant.Int && constant.BitLen(x.val) > limit {
+	const prec = 512 // 512 is the constant precision
+	if x.val.Kind() == constant.Int && constant.BitLen(x.val) > prec {
 		check.errorf(pos, "constant %s overflow", what)
 		x.val = constant.MakeUnknown()
 	}
 }
 
-// This is only used for operations that may cause overflow.
-var op2str = [...]string{
+// opName returns the name of an operation, or the empty string.
+// For now, only operations that might overflow are handled.
+// TODO(gri) Expand this to a general mechanism giving names to
+//           nodes?
+func opName(e *syntax.Operation) string {
+	op := int(e.Op)
+	if e.Y == nil {
+		if op < len(op2str1) {
+			return op2str1[op]
+		}
+	} else {
+		if op < len(op2str2) {
+			return op2str2[op]
+		}
+	}
+	return ""
+}
+
+// Entries must be "" or end with a space.
+var op2str1 = [...]string{
+	syntax.Xor: "bitwise complement",
+}
+
+var op2str2 = [...]string{
 	syntax.Add: "addition",
 	syntax.Sub: "subtraction",
 	syntax.Xor: "bitwise XOR",
@@ -800,8 +820,17 @@ func (check *Checker) shift(x, y *operand, e syntax.Expr, op syntax.Operator) {
 
 	if x.mode == constant_ {
 		if y.mode == constant_ {
+			// if either x or y has an unknown value, the result is unknown
+			if x.val.Kind() == constant.Unknown || y.val.Kind() == constant.Unknown {
+				x.val = constant.MakeUnknown()
+				// ensure the correct type - see comment below
+				if !isInteger(x.typ) {
+					x.typ = Typ[UntypedInt]
+				}
+				return
+			}
 			// rhs must be within reasonable bounds in constant shifts
-			const shiftBound = 1023 - 1 + 52 // so we can express smallestFloat64
+			const shiftBound = 1023 - 1 + 52 // so we can express smallestFloat64 (see issue #44057)
 			s, ok := constant.Uint64Val(y.val)
 			if !ok || s > shiftBound {
 				check.invalidOpf(y, "invalid shift count %s", y)

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

@@ -182,7 +182,6 @@ func TestStdFixed(t *testing.T) {
 		"issue16369.go",  // go/types handles this correctly - not an issue
 		"issue18459.go",  // go/types doesn't check validity of //go:xxx directives
 		"issue18882.go",  // go/types doesn't check validity of //go:xxx directives
-		"issue20232.go",  // go/types handles larger constants than gc
 		"issue20529.go",  // go/types does not have constraints on stack size
 		"issue22200.go",  // go/types does not have constraints on stack size
 		"issue22200b.go", // go/types does not have constraints on stack size

src/cmd/compile/internal/types2/testdata/builtins.src

@@ -514,7 +514,7 @@ func panic1() {
 	panic("foo")
 	panic(false)
 	panic(1<<10)
-	panic(1 /* ERROR overflows */ <<1000)
+	panic(1 << /* ERROR constant shift overflow */ 1000)
 	_ = panic /* ERROR used as value */ (0)
 
 	var s []byte
@@ -538,7 +538,7 @@ func print1() {
 	print(2.718281828)
 	print(false)
 	print(1<<10)
-	print(1 /* ERROR overflows */ <<1000)
+	print(1 << /* ERROR constant shift overflow */ 1000)
 	println(nil /* ERROR untyped nil */ )
 
 	var s []int
@@ -564,7 +564,7 @@ func println1() {
 	println(2.718281828)
 	println(false)
 	println(1<<10)
-	println(1 /* ERROR overflows */ <<1000)
+	println(1 << /* ERROR constant shift overflow */ 1000)
 	println(nil /* ERROR untyped nil */ )
 
 	var s []int
@@ -695,7 +695,7 @@ func Alignof1() {
 	_ = unsafe.Alignof(42)
 	_ = unsafe.Alignof(new(struct{}))
 	_ = unsafe.Alignof(1<<10)
-	_ = unsafe.Alignof(1 /* ERROR overflows */ <<1000)
+	_ = unsafe.Alignof(1 << /* ERROR constant shift overflow */ 1000)
 	_ = unsafe.Alignof(nil /* ERROR "untyped nil */ )
 	unsafe /* ERROR not used */ .Alignof(x)
 
@@ -783,7 +783,7 @@ func Sizeof1() {
 	_ = unsafe.Sizeof(42)
 	_ = unsafe.Sizeof(new(complex128))
 	_ = unsafe.Sizeof(1<<10)
-	_ = unsafe.Sizeof(1 /* ERROR overflows */ <<1000)
+	_ = unsafe.Sizeof(1 << /* ERROR constant shift overflow */ 1000)
 	_ = unsafe.Sizeof(nil /* ERROR untyped nil */ )
 	unsafe /* ERROR not used */ .Sizeof(x)
 

src/cmd/compile/internal/types2/testdata/const0.src

@@ -350,9 +350,14 @@ const _ = unsafe.Sizeof(func() {
 })
 
 // untyped constants must not get arbitrarily large
-const (
-	huge = 1<<1000
-	// TODO(gri) here the errors should be at the last operator not the last operand
-	_ = huge * huge * huge   // ERROR constant multiplication overflow
-	_ = huge << 1000 << 1000 // ERROR constant shift overflow
-)
+const prec = 512 // internal maximum precision for integers
+const maxInt = (1<<(prec/2) - 1) * (1<<(prec/2) + 1) // == 1<<prec - 1
+
+const _ = maxInt + /* ERROR constant addition overflow */ 1
+const _ = -maxInt - /* ERROR constant subtraction overflow */ 1
+const _ = maxInt ^ /* ERROR constant bitwise XOR overflow */ -1
+const _ = maxInt * /* ERROR constant multiplication overflow */ 2
+const _ = maxInt << /* ERROR constant shift overflow */ 2
+const _ = 1 << /* ERROR constant shift overflow */ prec
+
+const _ = ^ /* ERROR constant bitwise complement overflow */ maxInt

src/cmd/compile/internal/types2/testdata/const1.src

@@ -43,7 +43,12 @@ const (
 
 const (
 	smallestFloat32 = 1.0 / (1<<(127 - 1 + 23))
-	smallestFloat64 = 1.0 / (1<<(1023 - 1 + 52))
+	// TODO(gri) The compiler limits integers to 512 bit and thus
+	//           we cannot compute the value (1<<(1023 - 1 + 52))
+	//           without overflow. For now we match the compiler.
+	//           See also issue #44057.
+	// smallestFloat64 = 1.0 / (1<<(1023 - 1 + 52))
+	smallestFloat64 = 4.940656458412465441765687928682213723651e-324
 )
 
 const (
@@ -53,7 +58,12 @@ const (
 
 const (
 	maxFloat32 = 1<<127 * (1<<24 - 1) / (1.0<<23)
-	maxFloat64 = 1<<1023 * (1<<53 - 1) / (1.0<<52)
+	// TODO(gri) The compiler limits integers to 512 bit and thus
+	//           we cannot compute the value 1<<1023
+	//           without overflow. For now we match the compiler.
+	//           See also issue #44057.
+	// maxFloat64 = 1<<1023 * (1<<53 - 1) / (1.0<<52)
+	maxFloat64 = 1.797693134862315708145274237317043567981e+308
 )
 
 const (
@@ -271,7 +281,9 @@ const (
 	_ = assert(float64(smallestFloat32) == smallestFloat32)
 	_ = assert(float64(smallestFloat32/2) == smallestFloat32/2)
 	_ = assert(float64(smallestFloat64) == smallestFloat64)
-	_ = assert(float64(smallestFloat64/2) == 0)
+	// TODO(gri) With the change to the declaration of smallestFloat64
+	//           this now fails to be true. See issue #44058.
+	// _ = assert(float64(smallestFloat64/2) == 0)
 )
 
 const (

test/run.go

@@ -1978,5 +1978,4 @@ var excluded = map[string]bool{
 	"fixedbugs/issue7525c.go":  true, // types2 reports init cycle error on different line - ok otherwise
 	"fixedbugs/issue7525d.go":  true, // types2 reports init cycle error on different line - ok otherwise
 	"fixedbugs/issue7525e.go":  true, // types2 reports init cycle error on different line - ok otherwise
-	"fixedbugs/issue7746.go":   true, // types2 reports overflow on a different line
 }