cmd: use cmd/internal/hash.New32 and Sum32 only

Do not use New16, New20, Sum16, Sum20 anymore.
As of CL 641096, these are just wrappers around New32 and Sum32.
Change call sites to use them directly.

Change-Id: Icea91a77449f6839b903894997057ba404bd04e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/641076
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/cgo/main.go

@@ -390,7 +390,7 @@ func main() {
 	// We already put _cgo_ at the beginning, so the main
 	// concern is other cgo wrappers for the same functions.
 	// Use the beginning of the 16 bytes hash of the input to disambiguate.
-	h := hash.New16()
+	h := hash.New32()
 	io.WriteString(h, *importPath)
 	var once sync.Once
 	var wg sync.WaitGroup

src/cmd/compile/internal/liveness/plive.go

@@ -981,7 +981,7 @@ func (lv *Liveness) enableClobber() {
 		// Clobber only functions where the hash of the function name matches a pattern.
 		// Useful for binary searching for a miscompiled function.
 		hstr := ""
-		for _, b := range hash.Sum20([]byte(lv.f.Name)) {
+		for _, b := range hash.Sum32([]byte(lv.f.Name)) {
 			hstr += fmt.Sprintf("%08b", b)
 		}
 		if !strings.HasSuffix(hstr, h) {

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

@@ -646,7 +646,7 @@ func SplitVargenSuffix(name string) (base, suffix string) {
 func TypeHash(t *Type) uint32 {
 	p := t.LinkString()
 
-	// Using 16 bytes hash is overkill, but reduces accidental collisions.
-	h := hash.Sum16([]byte(p))
+	// Using a cryptographic hash is overkill but minimizes accidental collisions.
+	h := hash.Sum32([]byte(p))
 	return binary.LittleEndian.Uint32(h[:4])
 }

src/cmd/internal/hash/hash.go

@@ -5,69 +5,26 @@
 // Package hash implements hash functions used in the compiler toolchain.
 package hash
 
-// TODO(rsc): Delete the 16 and 20 forms and use 32 at all call sites.
-
 import (
 	"crypto/sha256"
 	"hash"
 )
 
-const (
-	// Size32 is the size of the 32-byte hash checksum.
-	Size32 = 32
-	// Size20 is the size of the 20-byte hash checksum.
-	Size20 = 20
-	// Size16 is the size of the 16-byte hash checksum.
-	Size16 = 16
-)
+// Size32 is the size of the 32-byte hash functions [New32] and [Sum32].
+const Size32 = 32
 
-type shortHash struct {
-	hash.Hash
-	n int
-}
-
-func (h *shortHash) Sum(b []byte) []byte {
-	old := b
-	sum := h.Hash.Sum(b)
-	return sum[:len(old)+h.n]
-}
-
-// New32 returns a new [hash.Hash] computing the 32 bytes hash checksum.
+// New32 returns a new [hash.Hash] computing the 32-byte hash checksum.
+// Note that New32 and [Sum32] compute different hashes.
 func New32() hash.Hash {
 	h := sha256.New()
 	_, _ = h.Write([]byte{1}) // make this hash different from sha256
 	return h
 }
 
-// New20 returns a new [hash.Hash] computing the 20 bytes hash checksum.
-func New20() hash.Hash {
-	return &shortHash{New32(), 20}
-}
-
-// New16 returns a new [hash.Hash] computing the 16 bytes hash checksum.
-func New16() hash.Hash {
-	return &shortHash{New32(), 16}
-}
-
-// Sum32 returns the 32 bytes checksum of the data.
-func Sum32(data []byte) [Size32]byte {
+// Sum32 returns a 32-byte checksum of the data.
+// Note that Sum32 and [New32] compute different hashes.
+func Sum32(data []byte) [32]byte {
 	sum := sha256.Sum256(data)
-	sum[0] ^= 1 // make this hash different from sha256
+	sum[0] ^= 0xff // make this hash different from sha256
 	return sum
 }
-
-// Sum20 returns the 20 bytes checksum of the data.
-func Sum20(data []byte) [Size20]byte {
-	sum := Sum32(data)
-	var short [Size20]byte
-	copy(short[:], sum[4:])
-	return short
-}
-
-// Sum16 returns the 16 bytes checksum of the data.
-func Sum16(data []byte) [Size16]byte {
-	sum := Sum32(data)
-	var short [Size16]byte
-	copy(short[:], sum[8:])
-	return short
-}

src/cmd/internal/obj/objfile.go

@@ -494,7 +494,7 @@ func contentHash64(s *LSym) goobj.Hash64Type {
 // For now, we assume there is no circular dependencies among
 // hashed symbols.
 func (w *writer) contentHash(s *LSym) goobj.HashType {
-	h := hash.New20()
+	h := hash.New32()
 	var tmp [14]byte
 
 	// Include the size of the symbol in the hash.

src/cmd/internal/obj/sym.go

@@ -216,7 +216,7 @@ func (ctxt *Link) Int128Sym(hi, lo int64) *LSym {
 
 // GCLocalsSym generates a content-addressable sym containing data.
 func (ctxt *Link) GCLocalsSym(data []byte) *LSym {
-	sum := hash.Sum16(data)
+	sum := hash.Sum32(data)
 	str := base64.StdEncoding.EncodeToString(sum[:16])
 	return ctxt.LookupInit(fmt.Sprintf("gclocals·%s", str), func(lsym *LSym) {
 		lsym.P = data

src/cmd/link/internal/ld/elf.go

@@ -1690,11 +1690,11 @@ func (ctxt *Link) doelf() {
 		sb.SetType(sym.SRODATA)
 		ldr.SetAttrSpecial(s, true)
 		sb.SetReachable(true)
-		sb.SetSize(hash.Size20)
+		sb.SetSize(hash.Size32)
 		slices.SortFunc(ctxt.Library, func(a, b *sym.Library) int {
 			return strings.Compare(a.Pkg, b.Pkg)
 		})
-		h := hash.New20()
+		h := hash.New32()
 		for _, l := range ctxt.Library {
 			h.Write(l.Fingerprint[:])
 		}

src/cmd/link/internal/ld/lib.go

@@ -1022,7 +1022,7 @@ func typeSymbolMangle(name string) string {
 		return name
 	}
 	if isType {
-		hb := hash.Sum20([]byte(name[5:]))
+		hb := hash.Sum32([]byte(name[5:]))
 		prefix := "type:"
 		if name[5] == '.' {
 			prefix = "type:."
@@ -1035,7 +1035,7 @@ func typeSymbolMangle(name string) string {
 	if j == -1 || j <= i {
 		j = len(name)
 	}
-	hb := hash.Sum20([]byte(name[i+1 : j]))
+	hb := hash.Sum32([]byte(name[i+1 : j]))
 	return name[:i+1] + base64.StdEncoding.EncodeToString(hb[:6]) + name[j:]
 }
 

src/cmd/objdump/objdump_test.go

@@ -134,9 +134,9 @@ func testDisasm(t *testing.T, srcfname string, printCode bool, printGnuAsm bool,
 		goarch = f[1]
 	}
 
-	hash := hash.Sum16([]byte(fmt.Sprintf("%v-%v-%v-%v", srcfname, flags, printCode, printGnuAsm)))
+	hash := hash.Sum32([]byte(fmt.Sprintf("%v-%v-%v-%v", srcfname, flags, printCode, printGnuAsm)))
 	tmp := t.TempDir()
-	hello := filepath.Join(tmp, fmt.Sprintf("hello-%x.exe", hash))
+	hello := filepath.Join(tmp, fmt.Sprintf("hello-%x.exe", hash[:16]))
 	args := []string{"build", "-o", hello}
 	args = append(args, flags...)
 	args = append(args, srcfname)