Go has optimizing compilers and linkers which are constantly being improved.
The following example of your program reduces the call to test3 to
MOVQ $0x82, 0(SP)
where 0x82 = 130 = 42 * 3 + 4
$ cat xiecui.go
package main
func test3(a int) int {
return a*3 + 4
}
func main() {
a := 42
t := test3(a)
println(t)
}
$ go version
go version devel +758ac371ab Tue Aug 25 21:15:43 2020 +0000 linux/amd64
$ go build xiecui.go
$ ./xiecui
130
$ go tool compile -S xiecui.go > xiecui.compile
"".test3 STEXT nosplit size=19 args=0x10 locals=0x0 funcid=0x0
0x0000 00000 (xiecui.go:3) TEXT "".test3(SB),
NOSPLIT|ABIInternal, $0-16
0x0000 00000 (xiecui.go:3) FUNCDATA $0,
gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (xiecui.go:3) FUNCDATA $1,
gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (xiecui.go:4) MOVQ "".a+8(SP), AX
0x0005 00005 (xiecui.go:4) LEAQ (AX)(AX*2), AX
0x0009 00009 (xiecui.go:4) LEAQ 4(AX), AX
0x000d 00013 (xiecui.go:4) MOVQ AX, "".~r1+16(SP)
0x0012 00018 (xiecui.go:4) RET
"".main STEXT size=77 args=0x0 locals=0x10 funcid=0x0
0x0000 00000 (xiecui.go:7) TEXT "".main(SB), ABIInternal, $16-0
0x0000 00000 (xiecui.go:7) MOVQ (TLS), CX
0x0009 00009 (xiecui.go:7) CMPQ SP, 16(CX)
0x000d 00013 (xiecui.go:7) PCDATA $0, $-2
0x000d 00013 (xiecui.go:7) JLS 70
0x000f 00015 (xiecui.go:7) PCDATA $0, $-1
0x000f 00015 (xiecui.go:7) SUBQ $16, SP
0x0013 00019 (xiecui.go:7) MOVQ BP, 8(SP)
0x0018 00024 (xiecui.go:7) LEAQ 8(SP), BP
0x001d 00029 (xiecui.go:7) FUNCDATA $0,
gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x001d 00029 (xiecui.go:7) FUNCDATA $1,
gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x001d 00029 (xiecui.go:10) PCDATA $1, $0
0x001d 00029 (xiecui.go:10) NOP
0x0020 00032 (xiecui.go:10) CALL runtime.printlock(SB)
0x0025 00037 (xiecui.go:10) MOVQ $130, (SP)
0x002d 00045 (xiecui.go:10) CALL runtime.printint(SB)
0x0032 00050 (xiecui.go:10) CALL runtime.printnl(SB)
0x0037 00055 (xiecui.go:10) CALL runtime.printunlock(SB)
0x003c 00060 (xiecui.go:11) MOVQ 8(SP), BP
0x0041 00065 (xiecui.go:11) ADDQ $16, SP
0x0045 00069 (xiecui.go:11) RET
0x0046 00070 (xiecui.go:11) NOP
0x0046 00070 (xiecui.go:7) PCDATA $1, $-1
0x0046 00070 (xiecui.go:7) PCDATA $0, $-2
0x0046 00070 (xiecui.go:7) CALL runtime.morestack_noctxt(SB)
0x004b 00075 (xiecui.go:7) PCDATA $0, $-1
0x004b 00075 (xiecui.go:7) JMP 0
$ go tool objdump xiecui > xiecui.objdump
TEXT main.main(SB) /home/peter/Sync/gopath/mod/nuts/xiecui.go
xiecui.go:7 0x45cc80 64488b0c25f8ffffff MOVQ
FS:0xfffffff8, CX
xiecui.go:7 0x45cc89 483b6110 CMPQ 0x10(CX), SP
xiecui.go:7 0x45cc8d 7637 JBE 0x45ccc6
xiecui.go:7 0x45cc8f 4883ec10 SUBQ $0x10, SP
xiecui.go:7 0x45cc93 48896c2408 MOVQ BP, 0x8(SP)
xiecui.go:7 0x45cc98 488d6c2408 LEAQ 0x8(SP), BP
xiecui.go:10 0x45cc9d 0f1f00 NOPL 0(AX)
xiecui.go:10 0x45cca0 e89b17fdff CALL
runtime.printlock(SB)
xiecui.go:10 0x45cca5 48c7042482000000 MOVQ $0x82,
0(SP)
xiecui.go:10 0x45ccad e8ae1ffdff CALL
runtime.printint(SB)
xiecui.go:10 0x45ccb2 e8491afdff CALL
runtime.printnl(SB)
xiecui.go:10 0x45ccb7 e80418fdff CALL
runtime.printunlock(SB)
xiecui.go:11 0x45ccbc 488b6c2408 MOVQ 0x8(SP), BP
xiecui.go:11 0x45ccc1 4883c410 ADDQ $0x10, SP
xiecui.go:11 0x45ccc5 c3 RET
xiecui.go:7 0x45ccc6 e8d5b0ffff CALL
runtime.morestack_noctxt(SB)
xiecui.go:7 0x45cccb ebb3 JMP main.main(SB)
$
Peter
On Tuesday, August 25, 2020 at 11:04:15 PM UTC-4 cuiw...@gmail.com wrote:
> function:
> func test3(a int) int {
> return a * 3 + 4
> }
>
> go version go1.13.5 darwin/amd64
> generate instructions:
> LEAQ (AX)(AX*2), AX
> LEAQ 4(AX), AX
>
> As far as i known，there a better choice
> LEAQ 4(AX*3), AX
>
> Can it be optimized?
>
>
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