From: Than McIntosh <thanm@google.com>
Date: Fri, 1 May 2020 16:24:03 +0000 (-0400)
Subject: [dev.link] cmd/internal/dwarf: revise Abbrevs() signature
X-Git-Tag: go1.16beta1~1378^2~159
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=6ea7a196d0a04eb913e0136fb681610055cf9b11;p=gostls13.git

[dev.link] cmd/internal/dwarf: revise Abbrevs() signature

The function Abbrevs() was returning an array of structures by value,
which is not very efficient (this was showing up in a kubernetes
kubelet linker profile). Switch the function to return a slice
instead.

Improves linker DwarfGenerateDebugSyms running time when
linking the compiler in compilebench:

DwarfGenerateDebugSyms   29.2ms ±144%  23.9ms ±125%  -17.89%  (p=0.000 n=99+99)

Change-Id: I1132816563f208c63eb82a7932d9f2bcb2455324
Reviewed-on: https://go-review.googlesource.com/c/go/+/231558
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
---

diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go
index a17b574cdd..db013999da 100644
--- a/src/cmd/internal/dwarf/dwarf.go
+++ b/src/cmd/internal/dwarf/dwarf.go
@@ -398,9 +398,9 @@ func expandPseudoForm(form uint8) uint8 {
 
 // Abbrevs() returns the finalized abbrev array for the platform,
 // expanding any DW_FORM pseudo-ops to real values.
-func Abbrevs() [DW_NABRV]dwAbbrev {
+func Abbrevs() []dwAbbrev {
 	if abbrevsFinalized {
-		return abbrevs
+		return abbrevs[:]
 	}
 	for i := 1; i < DW_NABRV; i++ {
 		for j := 0; j < len(abbrevs[i].attr); j++ {
@@ -408,7 +408,7 @@ func Abbrevs() [DW_NABRV]dwAbbrev {
 		}
 	}
 	abbrevsFinalized = true
-	return abbrevs
+	return abbrevs[:]
 }
 
 // abbrevs is a raw table of abbrev entries; it needs to be post-processed