sort: simplify bootstrap

We compile package sort as part of the compiler bootstrap,
to make sure the compiler uses a consistent sort algorithm
no matter what version of Go it is compiled against.
(This matters for elements that compare "equal" but are distinguishable.)

Package sort was compiled in such a way as to disallow
sort.Slice entirely during bootstrap (at least with some compilers),
while cmd/internal/obj was compiled in such a way as to
make obj.SortSlice available to all compilers, precisely because
sort.Slice was not. This is all highly confusing.
Simplify by making sort.Slice available all the time.

Followup to CL 169137 and #30440
(and also CL 40114 and CL 73951).

Change-Id: I127f4e02d6c71392805d256c3a90ef7c51f9ba0c
Reviewed-on: https://go-review.googlesource.com/c/go/+/174525
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/iexport.go

@@ -202,12 +202,12 @@ import (
 	"bufio"
 	"bytes"
 	"cmd/compile/internal/types"
-	"cmd/internal/obj"
 	"cmd/internal/src"
 	"encoding/binary"
 	"fmt"
 	"io"
 	"math/big"
+	"sort"
 	"strings"
 )
 
@@ -321,12 +321,12 @@ func (w *exportWriter) writeIndex(index map[*Node]uint64, mainIndex bool) {
 	for pkg, objs := range pkgObjs {
 		pkgs = append(pkgs, pkg)
 
-		obj.SortSlice(objs, func(i, j int) bool {
+		sort.Slice(objs, func(i, j int) bool {
 			return objs[i].Sym.Name < objs[j].Sym.Name
 		})
 	}
 
-	obj.SortSlice(pkgs, func(i, j int) bool {
+	sort.Slice(pkgs, func(i, j int) bool {
 		return pkgs[i].Path < pkgs[j].Path
 	})
 

src/cmd/compile/internal/gc/main.go

@@ -27,6 +27,7 @@ import (
 	"path"
 	"regexp"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -723,7 +724,7 @@ func Main(archInit func(*Arch)) {
 	}
 
 	// Check whether any of the functions we have compiled have gigantic stack frames.
-	obj.SortSlice(largeStackFrames, func(i, j int) bool {
+	sort.Slice(largeStackFrames, func(i, j int) bool {
 		return largeStackFrames[i].pos.Before(largeStackFrames[j].pos)
 	})
 	for _, large := range largeStackFrames {
@@ -1313,7 +1314,7 @@ func clearImports() {
 		}
 	}
 
-	obj.SortSlice(unused, func(i, j int) bool { return unused[i].pos.Before(unused[j].pos) })
+	sort.Slice(unused, func(i, j int) bool { return unused[i].pos.Before(unused[j].pos) })
 	for _, pkg := range unused {
 		pkgnotused(pkg.pos, pkg.path, pkg.name)
 	}

src/cmd/compile/internal/gc/obj.go

@@ -14,6 +14,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"sort"
 	"strconv"
 )
 
@@ -259,7 +260,7 @@ func dumpglobls() {
 		}
 	}
 
-	obj.SortSlice(funcsyms, func(i, j int) bool {
+	sort.Slice(funcsyms, func(i, j int) bool {
 		return funcsyms[i].LinksymName() < funcsyms[j].LinksymName()
 	})
 	for _, s := range funcsyms {

src/cmd/compile/internal/gc/pgen.go

@@ -348,7 +348,7 @@ func compileFunctions() {
 			// Compile the longest functions first,
 			// since they're most likely to be the slowest.
 			// This helps avoid stragglers.
-			obj.SortSlice(compilequeue, func(i, j int) bool {
+			sort.Slice(compilequeue, func(i, j int) bool {
 				return compilequeue[i].Nbody.Len() > compilequeue[j].Nbody.Len()
 			})
 		}

src/cmd/compile/internal/types/sym_test.go

@@ -6,8 +6,8 @@ package types_test
 
 import (
 	"cmd/compile/internal/types"
-	"cmd/internal/obj"
 	"reflect"
+	"sort"
 	"testing"
 )
 
@@ -50,7 +50,7 @@ func TestSymLess(t *testing.T) {
 	if reflect.DeepEqual(data, want) {
 		t.Fatal("data must be shuffled")
 	}
-	obj.SortSlice(data, func(i, j int) bool { return data[i].Less(data[j]) })
+	sort.Slice(data, func(i, j int) bool { return data[i].Less(data[j]) })
 	if !reflect.DeepEqual(data, want) {
 		t.Logf("want: %#v", want)
 		t.Logf("data: %#v", data)

src/cmd/internal/obj/bootstrap.go

@@ -1,34 +0,0 @@
-// Copyright 2017 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.
-
-// +build !go1.8
-
-package obj
-
-import (
-	"reflect"
-	"sort"
-)
-
-func SortSlice(slice interface{}, less func(i, j int) bool) {
-	val := reflect.ValueOf(slice)
-	tmp := reflect.New(val.Type().Elem()).Elem()
-	x := sliceByFn{val: val, tmp: tmp, less: less}
-	sort.Sort(x)
-}
-
-type sliceByFn struct {
-	val  reflect.Value
-	tmp  reflect.Value
-	less func(i, j int) bool
-}
-
-func (x sliceByFn) Len() int           { return x.val.Len() }
-func (x sliceByFn) Less(i, j int) bool { return x.less(i, j) }
-func (x sliceByFn) Swap(i, j int) {
-	a, b := x.val.Index(i), x.val.Index(j)
-	x.tmp.Set(a)
-	a.Set(b)
-	b.Set(x.tmp)
-}

src/cmd/internal/obj/objfile.go

@@ -104,7 +104,7 @@ func WriteObjFile(ctxt *Link, b *bufio.Writer) {
 		// As they are created during Progedit, two symbols can be switched between
 		// two different compilations. Therefore, BuildID will be different.
 		// TODO: find a better place and optimize to only sort TOC symbols
-		SortSlice(ctxt.Data, func(i, j int) bool {
+		sort.Slice(ctxt.Data, func(i, j int) bool {
 			return ctxt.Data[i].Name < ctxt.Data[j].Name
 		})
 	}

src/go/build/deps_test.go

@@ -586,9 +586,8 @@ func findImports(pkg string) ([]string, error) {
 	var haveImport = map[string]bool{}
 	for _, file := range files {
 		name := file.Name()
-		if name == "slice_pre113.go" {
-			// This file is ignored by build tags which aren't
-			// handled by this findImports func.
+		if name == "slice_go14.go" || name == "slice_go18.go" {
+			// These files are for compiler bootstrap with older versions of Go and not built in the standard build.
 			continue
 		}
 		if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {

src/sort/slice.go

@@ -2,14 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !compiler_bootstrap go1.13
-
 package sort
 
-import (
-	"internal/reflectlite"
-)
-
 // Slice sorts the provided slice given the provided less function.
 //
 // The sort is not guaranteed to be stable. For a stable sort, use
@@ -17,8 +11,8 @@ import (
 //
 // The function panics if the provided interface is not a slice.
 func Slice(slice interface{}, less func(i, j int) bool) {
-	rv := reflectlite.ValueOf(slice)
-	swap := reflectlite.Swapper(slice)
+	rv := reflectValueOf(slice)
+	swap := reflectSwapper(slice)
 	length := rv.Len()
 	quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))
 }
@@ -28,8 +22,8 @@ func Slice(slice interface{}, less func(i, j int) bool) {
 //
 // The function panics if the provided interface is not a slice.
 func SliceStable(slice interface{}, less func(i, j int) bool) {
-	rv := reflectlite.ValueOf(slice)
-	swap := reflectlite.Swapper(slice)
+	rv := reflectValueOf(slice)
+	swap := reflectSwapper(slice)
 	stable_func(lessSwap{less, swap}, rv.Len())
 }
 
@@ -37,7 +31,7 @@ func SliceStable(slice interface{}, less func(i, j int) bool) {
 //
 // The function panics if the provided interface is not a slice.
 func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool {
-	rv := reflectlite.ValueOf(slice)
+	rv := reflectValueOf(slice)
 	n := rv.Len()
 	for i := n - 1; i > 0; i-- {
 		if less(i, i-1) {

src/sort/slice_go113.go

@@ -0,0 +1,12 @@
+// Copyright 2017 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.
+
+// +build go1.13
+
+package sort
+
+import "internal/reflectlite"
+
+var reflectValueOf = reflectlite.ValueOf
+var reflectSwapper = reflectlite.Swapper

src/sort/slice_go14.go

@@ -0,0 +1,22 @@
+// Copyright 2017 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.
+
+// +build !go1.8
+
+package sort
+
+import "reflect"
+
+var reflectValueOf = reflect.ValueOf
+
+func reflectSwapper(x interface{}) func(int, int) {
+	v := reflectValueOf(x)
+	tmp := reflect.New(v.Type().Elem()).Elem()
+	return func(i, j int) {
+		a, b := v.Index(i), v.Index(j)
+		tmp.Set(a)
+		a.Set(b)
+		b.Set(tmp)
+	}
+}

src/sort/slice_go18.go

@@ -2,12 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build go1.8
+// +build go1.8,!go1.13
 
-package obj
+package sort
 
-import "sort"
+import "reflect"
 
-func SortSlice(slice interface{}, less func(i, j int) bool) {
-	sort.Slice(slice, less)
-}
+var reflectValueOf = reflect.ValueOf
+var reflectSwapper = reflect.Swapper

src/sort/slice_pre113.go

@@ -1,46 +0,0 @@
-// Copyright 2017 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.
-
-// +build go1.8,!go1.13
-
-package sort
-
-import "reflect"
-
-// Slice sorts the provided slice given the provided less function.
-//
-// The sort is not guaranteed to be stable. For a stable sort, use
-// SliceStable.
-//
-// The function panics if the provided interface is not a slice.
-func Slice(slice interface{}, less func(i, j int) bool) {
-	rv := reflect.ValueOf(slice)
-	swap := reflect.Swapper(slice)
-	length := rv.Len()
-	quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))
-}
-
-// SliceStable sorts the provided slice given the provided less
-// function while keeping the original order of equal elements.
-//
-// The function panics if the provided interface is not a slice.
-func SliceStable(slice interface{}, less func(i, j int) bool) {
-	rv := reflect.ValueOf(slice)
-	swap := reflect.Swapper(slice)
-	stable_func(lessSwap{less, swap}, rv.Len())
-}
-
-// SliceIsSorted tests whether a slice is sorted.
-//
-// The function panics if the provided interface is not a slice.
-func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool {
-	rv := reflect.ValueOf(slice)
-	n := rv.Len()
-	for i := n - 1; i > 0; i-- {
-		if less(i, i-1) {
-			return false
-		}
-	}
-	return true
-}