From: Zeke Lu <lvzecai@gmail.com>
Date: Tue, 4 Oct 2022 07:10:09 +0000 (+0000)
Subject: reflect: avoid unnecessary copy of funcTypes
X-Git-Tag: go1.20rc1~741
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=e7d203f494281a229a7d4ef769f14975e9b12e4e;p=gostls13.git

reflect: avoid unnecessary copy of funcTypes

Imagine that initFuncTypes is called with n=3, funcTypes will be
[nil, nil, nil, **reflect.rtype] afterward, then it's called with n=2.
The current implementation will copy funcTypes because funcTypes[2] is
nil. This is unnecessary. It should make a new slice and copy funcTypes
into it only when n >= len(funcTypes).

Updates #56011.

Change-Id: Ia093d2f550d6924a4c58bcd21325093e32b40baa
GitHub-Last-Rev: a599eae7c2f6a388dfe1ff39cf61fd645885a64d
GitHub-Pull-Request: golang/go#56024
Reviewed-on: https://go-review.googlesource.com/c/go/+/438395
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
---

diff --git a/src/reflect/type.go b/src/reflect/type.go
index 339c982087..b06b7ffd9e 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -2005,13 +2005,15 @@ var funcTypesMutex sync.Mutex
 func initFuncTypes(n int) Type {
 	funcTypesMutex.Lock()
 	defer funcTypesMutex.Unlock()
-	if n < len(funcTypes) && funcTypes[n] != nil {
+	if n >= len(funcTypes) {
+		newFuncTypes := make([]Type, n+1)
+		copy(newFuncTypes, funcTypes)
+		funcTypes = newFuncTypes
+	}
+	if funcTypes[n] != nil {
 		return funcTypes[n]
 	}
 
-	newFuncTypes := make([]Type, n+1)
-	copy(newFuncTypes, funcTypes)
-	funcTypes = newFuncTypes
 	funcTypes[n] = StructOf([]StructField{
 		{
 			Name: "FuncType",