cmd/gc: teach componentgen about string constants
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>
diff --git a/src/cmd/internal/gc/gen.go b/src/cmd/internal/gc/gen.go
index 445efc9..1a7f76f 100644
--- a/src/cmd/internal/gc/gen.go
+++ b/src/cmd/internal/gc/gen.go
@@ -1135,6 +1135,8 @@
freel := 0
freer := 0
+ var isConstString bool
+
switch nl.Type.Etype {
default:
goto no
@@ -1178,9 +1180,10 @@
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 @@
if nr != nil {
nodr = *nr
- if !cadable(nr) {
+ if !cadable(nr) && !isConstString {
Igen(nr, &nodr, nil)
freer = 1
}
@@ -1275,7 +1278,13 @@
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 @@
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
}
