94410c794e
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> |
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