From 2692f48330da001903bc74210cec5ff27fe663c2 Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Fri, 24 Apr 2015 20:24:49 -0700
Subject: [PATCH] cmd/internal/ld: remove pointless allocs

Reduces allocs linking cmd/go and runtime.test
by ~13%. No functional changes.

The most easily addressed sources of allocations
after this are expandpkg, rdstring, and symbuf
string conversion.

These can be reduced by interning strings,
but that increases the overall memory footprint.

Change-Id: Ifedefc9f2a0403bcc75460d6b139e8408374e058
Reviewed-on: https://go-review.googlesource.com/9391
Reviewed-by: David Crawshaw <crawshaw@golang.org>
---
 src/cmd/internal/ld/dwarf.go   | 12 ++++++------
 src/cmd/internal/ld/go.go      |  8 ++------
 src/cmd/internal/ld/objfile.go | 18 +++++++++---------
 3 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/src/cmd/internal/ld/dwarf.go b/src/cmd/internal/ld/dwarf.go
index ec540fdd77..6d90404b13 100644
--- a/src/cmd/internal/ld/dwarf.go
+++ b/src/cmd/internal/ld/dwarf.go
@@ -158,16 +158,16 @@ func sleb128enc(v int64, dst []byte) int {
 	return int(length)
 }
 
+var encbuf [10]byte
+
 func uleb128put(v int64) {
-	var buf [10]byte
-	n := uleb128enc(uint64(v), buf[:])
-	Cwrite(buf[:n])
+	n := uleb128enc(uint64(v), encbuf[:])
+	Cwrite(encbuf[:n])
 }
 
 func sleb128put(v int64) {
-	var buf [10]byte
-	n := sleb128enc(v, buf[:])
-	Cwrite(buf[:n])
+	n := sleb128enc(v, encbuf[:])
+	Cwrite(encbuf[:n])
 }
 
 /*
diff --git a/src/cmd/internal/ld/go.go b/src/cmd/internal/ld/go.go
index e6756ab387..06f1d87e6a 100644
--- a/src/cmd/internal/ld/go.go
+++ b/src/cmd/internal/ld/go.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// go-specific code shared across loaders (5l, 6l, 8l).
+
 package ld
 
 import (
@@ -20,12 +22,6 @@ func expandpkg(t0 string, pkg string) string {
 	return strings.Replace(t0, `"".`, pkg+".", -1)
 }
 
-// Copyright 2009 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.
-
-// go-specific code shared across loaders (5l, 6l, 8l).
-
 // accumulate all type information from .6 files.
 // check for inconsistencies.
 
diff --git a/src/cmd/internal/ld/objfile.go b/src/cmd/internal/ld/objfile.go
index 41534c857c..8eac63497e 100644
--- a/src/cmd/internal/ld/objfile.go
+++ b/src/cmd/internal/ld/objfile.go
@@ -80,8 +80,7 @@ func readsym(ctxt *Link, f *Biobuf, pkg string, pn string) {
 	}
 	size := int(rdint(f))
 	typ := rdsym(ctxt, f, pkg)
-	var data []byte
-	rddata(f, &data)
+	data := rddata(f)
 	nreloc := int(rdint(f))
 
 	if v != 0 {
@@ -183,14 +182,14 @@ overwrite:
 
 		s.Pcln = new(Pcln)
 		pc := s.Pcln
-		rddata(f, &pc.Pcsp.P)
-		rddata(f, &pc.Pcfile.P)
-		rddata(f, &pc.Pcline.P)
+		pc.Pcsp.P = rddata(f)
+		pc.Pcfile.P = rddata(f)
+		pc.Pcline.P = rddata(f)
 		n = int(rdint(f))
 		pc.Pcdata = make([]Pcdata, n)
 		pc.Npcdata = n
 		for i := 0; i < n; i++ {
-			rddata(f, &pc.Pcdata[i].P)
+			pc.Pcdata[i].P = rddata(f)
 		}
 		n = int(rdint(f))
 		pc.Funcdata = make([]*LSym, n)
@@ -302,10 +301,11 @@ func rdstring(f *Biobuf) string {
 	return string(p)
 }
 
-func rddata(f *Biobuf, pp *[]byte) {
+func rddata(f *Biobuf) []byte {
 	n := rdint(f)
-	*pp = make([]byte, n)
-	Bread(f, *pp)
+	p := make([]byte, n)
+	Bread(f, p)
+	return p
 }
 
 var symbuf []byte
-- 
2.48.1