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cmd/gc: teach componentgen about string constants

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This makes it cheaper to copy string literals.
This happens just about anywhere that they are used.

Example:

func f() string {
	return "f"
}

Using 6g, compiler output before:

"".f t=1 size=32 value=0 args=0x10 locals=0x0
	0x0000 00000 (p.go:3)	TEXT	"".f+0(SB),4,$0-16
	0x0000 00000 (p.go:3)	FUNCDATA	$0,gclocals·d64e51a4c4bfeaa840e480961ec6b0b3+0(SB)
	0x0000 00000 (p.go:3)	FUNCDATA	$1,gclocals·3280bececceccd33cb74587feedb1f9f+0(SB)
	0x0000 00000 (p.go:4)	LEAQ	go.string."f"+0(SB),BX
	0x0007 00007 (p.go:4)	MOVQ	(BX),BP
	0x000a 00010 (p.go:4)	MOVQ	BP,"".~r0+8(FP)
	0x000f 00015 (p.go:4)	MOVQ	8(BX),BP
	0x0013 00019 (p.go:4)	MOVQ	BP,"".~r0+16(FP)
	0x0018 00024 (p.go:4)	RET	,

After:

"".f t=1 size=32 value=0 args=0x10 locals=0x0
	0x0000 00000 (p.go:3)	TEXT	"".f+0(SB),4,$0-16
	0x0000 00000 (p.go:3)	FUNCDATA	$0,gclocals·d64e51a4c4bfeaa840e480961ec6b0b3+0(SB)
	0x0000 00000 (p.go:3)	FUNCDATA	$1,gclocals·3280bececceccd33cb74587feedb1f9f+0(SB)
	0x0000 00000 (p.go:4)	MOVQ	$go.string."f"+16(SB),BX
	0x0007 00007 (p.go:4)	MOVQ	BX,"".~r0+8(FP)
	0x000c 00012 (p.go:4)	MOVQ	$1,"".~r0+16(FP)
	0x0015 00021 (p.go:4)	RET	,

The leading MOVQ here will be converted into a LEAQ by the linker,
but there is still a net reduction of two MOVQs.

Before:

TEXT main.f(SB)
        p.go:4  0x2000  488d1d49500500  LEAQ 0x55049(IP), BX
        p.go:4  0x2007  488b2b          MOVQ 0(BX), BP
        p.go:4  0x200a  48896c2408      MOVQ BP, 0x8(SP)
        p.go:4  0x200f  488b6b08        MOVQ 0x8(BX), BP
        p.go:4  0x2013  48896c2410      MOVQ BP, 0x10(SP)
        p.go:4  0x2018  c3              RET

After:

TEXT main.f(SB)
        p.go:4  0x2000  488d1dd94c0500          LEAQ 0x54cd9(IP), BX
        p.go:4  0x2007  48895c2408              MOVQ BX, 0x8(SP)
        p.go:4  0x200c  48c744241001000000      MOVQ $0x1, 0x10(SP)
        p.go:4  0x2015  c3                      RET

The performance improvement is small but widespread.

As a nice small example, net/url's sole benchmark using 6g:

benchmark           old ns/op     new ns/op     delta
BenchmarkString     16372         16118         -1.55%

And with 8g:

benchmark           old ns/op     new ns/op     delta
BenchmarkString     22034         21709         -1.47%

Change-Id: I4ce202ee7dbd4057be869e2faaaa638c28a1fff0
Reviewed-on: https://go-review.googlesource.com/2587
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Josh Bleecher Snyder 2015-01-08 15:30:02 -08:00
parent 297c1d297f
commit 94410c794e
1 changed files with 15 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

19
src/cmd/internal/gc/gen.go
View file

@ -1135,6 +1135,8 @@ func Componentgen(nr *Node, nl *Node) bool {
freel := 0
freer := 0
var isConstString bool
switch nl.Type.Etype {
default:
goto no
@ -1178,9 +1180,10 @@ func Componentgen(nr *Node, nl *Node) bool {
break
}
isConstString = Isconst(nr, CTSTR)
nodl = *nl
if !cadable(nl) {
if nr != nil && !cadable(nr) {
if nr != nil && !cadable(nr) && !isConstString {
goto no
}
Igen(nl, &nodl, nil)
@ -1189,7 +1192,7 @@ func Componentgen(nr *Node, nl *Node) bool {
if nr != nil {
nodr = *nr
if !cadable(nr) {
if !cadable(nr) && !isConstString {
Igen(nr, &nodr, nil)
freer = 1
}
@ -1275,7 +1278,13 @@ func Componentgen(nr *Node, nl *Node) bool {
nodl.Xoffset += int64(Array_array)
nodl.Type = Ptrto(Types[TUINT8])
if nr != nil {
if isConstString {
Regalloc(&nodr, Types[Tptr], nil)
p := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), nil, &nodr)
Datastring(nr.Val.U.Sval, &p.From)
p.From.Type = obj.TYPE_ADDR
Regfree(&nodr)
} else if nr != nil {
nodr.Xoffset += int64(Array_array)
nodr.Type = nodl.Type
}
@ -1285,7 +1294,9 @@ func Componentgen(nr *Node, nl *Node) bool {
nodl.Xoffset += int64(Array_nel) - int64(Array_array)
nodl.Type = Types[Simtype[TUINT]]
if nr != nil {
if isConstString {
Nodconst(&nodr, nodl.Type, int64(len(nr.Val.U.Sval)))
} else if nr != nil {
nodr.Xoffset += int64(Array_nel) - int64(Array_array)
nodr.Type = nodl.Type
}