From: Tomasz Jezierski <tjomek.jezierski@gmail.com>
Date: Mon, 1 Aug 2022 19:18:36 +0000 (+0200)
Subject: encoding/gob: replace runtime values with constants in init()
X-Git-Tag: go1.20rc1~1796
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=0f6ee42fe063a48d7825bc03097bbb714aafdb7d;p=gostls13.git

encoding/gob: replace runtime values with constants in init()

Current init() implementation in `encoding/gob/decode.go` checks int/uint/uintptr bit size with reflection in runtime. We could replace it with values available on compile stage. This should reduce time and allocations on binary start.
Results from GODEBUG=inittrace=1:
before:
init encoding/gob @4.4 ms, 0.21 ms clock, 43496 bytes, 652 allocs
after:
init encoding/gob @4.4 ms, 0.15 ms clock, 41672 bytes, 643 allocs

Updates #54184

Change-Id: I46dda2682fb92519da199415e29401d61edce697
Reviewed-on: https://go-review.googlesource.com/c/go/+/420455
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Rob Pike <r@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
---

diff --git a/src/encoding/gob/decode.go b/src/encoding/gob/decode.go
index eea2924f1a..7bca13c957 100644
--- a/src/encoding/gob/decode.go
+++ b/src/encoding/gob/decode.go
@@ -1228,9 +1228,14 @@ func (dec *Decoder) decodeIgnoredValue(wireId typeId) {
 	}
 }
 
+const (
+	intBits     = 32 << (^uint(0) >> 63)
+	uintptrBits = 32 << (^uintptr(0) >> 63)
+)
+
 func init() {
 	var iop, uop decOp
-	switch reflect.TypeOf(int(0)).Bits() {
+	switch intBits {
 	case 32:
 		iop = decInt32
 		uop = decUint32
@@ -1244,7 +1249,7 @@ func init() {
 	decOpTable[reflect.Uint] = uop
 
 	// Finally uintptr
-	switch reflect.TypeOf(uintptr(0)).Bits() {
+	switch uintptrBits {
 	case 32:
 		uop = decUint32
 	case 64: