go/types: implement unsafe.Add and unsafe.Slice

Updates #19367.
Updates #40481.

Change-Id: Id2b2d2e3e716f91f0dd9e5102689a1ba90a819e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/312213
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/go/types/builtins.go

@@ -586,6 +586,25 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 			check.recordBuiltinType(call.Fun, makeSig(x.typ))
 		}
 
+	case _Add:
+		// unsafe.Add(ptr unsafe.Pointer, len IntegerType) unsafe.Pointer
+		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
+		if x.mode == invalid {
+			return
+		}
+
+		var y operand
+		arg(&y, 1)
+		if !check.isValidIndex(&y, _InvalidUnsafeAdd, "length", true) {
+			return
+		}
+
+		x.mode = value
+		x.typ = Typ[UnsafePointer]
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(x.typ, x.typ, y.typ))
+		}
+
 	case _Alignof:
 		// unsafe.Alignof(x T) uintptr
 		if asTypeParam(x.typ) != nil {
@@ -663,6 +682,26 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		x.typ = Typ[Uintptr]
 		// result is constant - no need to record signature
 
+	case _Slice:
+		// unsafe.Slice(ptr *T, len IntegerType) []T
+		typ := asPointer(x.typ)
+		if typ == nil {
+			check.invalidArg(x, _InvalidUnsafeSlice, "%s is not a pointer", x)
+			return
+		}
+
+		var y operand
+		arg(&y, 1)
+		if !check.isValidIndex(&y, _InvalidUnsafeSlice, "length", false) {
+			return
+		}
+
+		x.mode = value
+		x.typ = NewSlice(typ.base)
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(x.typ, typ, y.typ))
+		}
+
 	case _Assert:
 		// assert(pred) causes a typechecker error if pred is false.
 		// The result of assert is the value of pred if there is no error.

src/go/types/builtins_test.go

@@ -107,6 +107,10 @@ var builtinCalls = []struct {
 	{"recover", `recover()`, `func() interface{}`},
 	{"recover", `_ = recover()`, `func() interface{}`},
 
+	{"Add", `var p unsafe.Pointer; _ = unsafe.Add(p, -1.0)`, `func(unsafe.Pointer, int) unsafe.Pointer`},
+	{"Add", `var p unsafe.Pointer; var n uintptr; _ = unsafe.Add(p, n)`, `func(unsafe.Pointer, uintptr) unsafe.Pointer`},
+	{"Add", `_ = unsafe.Add(nil, 0)`, `func(unsafe.Pointer, int) unsafe.Pointer`},
+
 	{"Alignof", `_ = unsafe.Alignof(0)`, `invalid type`},                 // constant
 	{"Alignof", `var x struct{}; _ = unsafe.Alignof(x)`, `invalid type`}, // constant
 
@@ -116,6 +120,9 @@ var builtinCalls = []struct {
 	{"Sizeof", `_ = unsafe.Sizeof(0)`, `invalid type`},                 // constant
 	{"Sizeof", `var x struct{}; _ = unsafe.Sizeof(x)`, `invalid type`}, // constant
 
+	{"Slice", `var p *int; _ = unsafe.Slice(p, 1)`, `func(*int, int) []int`},
+	{"Slice", `var p *byte; var n uintptr; _ = unsafe.Slice(p, n)`, `func(*byte, uintptr) []byte`},
+
 	{"assert", `assert(true)`, `invalid type`},                                    // constant
 	{"assert", `type B bool; const pred B = 1 < 2; assert(pred)`, `invalid type`}, // constant
 

src/go/types/check.go

@@ -329,14 +329,14 @@ func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type,
 }
 
 func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
-	// f must be a (possibly parenthesized) identifier denoting a built-in
-	// (built-ins in package unsafe always produce a constant result and
-	// we don't record their signatures, so we don't see qualified idents
-	// here): record the signature for f and possible children.
+	// f must be a (possibly parenthesized, possibly qualified)
+	// identifier denoting a built-in (including unsafe's non-constant
+	// functions Add and Slice): record the signature for f and possible
+	// children.
 	for {
 		check.recordTypeAndValue(f, builtin, sig, nil)
 		switch p := f.(type) {
-		case *ast.Ident:
+		case *ast.Ident, *ast.SelectorExpr:
 			return // we're done
 		case *ast.ParenExpr:
 			f = p.X

src/go/types/errorcodes.go

@@ -883,6 +883,45 @@ const (
 	//  var _ = real(int(1))
 	_InvalidReal
 
+	// _InvalidUnsafeAdd occurs when unsafe.Add is called with a
+	// length argument that is not of integer type.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var p unsafe.Pointer
+	//  var _ = unsafe.Add(p, float64(1))
+	_InvalidUnsafeAdd
+
+	// _InvalidUnsafeSlice occurs when unsafe.Slice is called with a
+	// pointer argument that is not of pointer type or a length argument
+	// that is not of integer type, negative, or out of bounds.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var x int
+	//  var _ = unsafe.Slice(x, 1)
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var x int
+	//  var _ = unsafe.Slice(&x, float64(1))
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var x int
+	//  var _ = unsafe.Slice(&x, -1)
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var x int
+	//  var _ = unsafe.Slice(&x, uint64(1) << 63)
+	_InvalidUnsafeSlice
+
 	/* exprs > assertion */
 
 	// _InvalidAssert occurs when a type assertion is applied to a

src/go/types/universe.go

@@ -137,9 +137,11 @@ const (
 	_Recover
 
 	// package unsafe
+	_Add
 	_Alignof
 	_Offsetof
 	_Sizeof
+	_Slice
 
 	// testing support
 	_Assert
@@ -168,9 +170,11 @@ var predeclaredFuncs = [...]struct {
 	_Real:    {"real", 1, false, expression},
 	_Recover: {"recover", 0, false, statement},
 
+	_Add:      {"Add", 2, false, expression},
 	_Alignof:  {"Alignof", 1, false, expression},
 	_Offsetof: {"Offsetof", 1, false, expression},
 	_Sizeof:   {"Sizeof", 1, false, expression},
+	_Slice:    {"Slice", 2, false, expression},
 
 	_Assert: {"assert", 1, false, statement},
 	_Trace:  {"trace", 0, true, statement},