```go
package main
type T struct {
a *int
}
func test(t *T, b *int) {
t.a = b
}
```
compile this code use cmd `go build -gcflags '-l' main.go`
only disable inline stage .
here is the plan9 assembly of function test
```assembly
TEXT main.test(SB) src/write-barrier/main.go
main.go:7 0x45ec60 64488b0c25f8ffffff MOVQ FS:0xfffffff8, CX
main.go:7 0x45ec69 483b6110 CMPQ 0x10(CX), SP
main.go:7 0x45ec6d 7639 JBE 0x45eca8
main.go:7 0x45ec6f 4883ec08 SUBQ $0x8, SP
main.go:7 0x45ec73 48892c24 MOVQ BP, 0(SP)
main.go:7 0x45ec77 488d2c24 LEAQ 0(SP), BP
main.go:8 0x45ec7b 488b7c2410 MOVQ 0x10(SP), DI
main.go:8 0x45ec80 8407 TESTB AL, 0(DI)
main.go:8 0x45ec82 833d379c090000 CMPL $0x0,
runtime.writeBarrier(SB)
main.go:8 0x45ec89 7511 JNE 0x45ec9c
main.go:8 0x45ec8b 488b442418 MOVQ 0x18(SP), AX
main.go:8 0x45ec90 488907 MOVQ AX, 0(DI)
main.go:9 0x45ec93 488b2c24 MOVQ 0(SP), BP
main.go:9 0x45ec97 4883c408 ADDQ $0x8, SP
main.go:9 0x45ec9b c3 RET
main.go:8 0x45ec9c 488b442418 MOVQ 0x18(SP), AX
main.go:8 0x45eca1 e8facaffff CALL
runtime.gcWriteBarrier(SB)
main.go:8 0x45eca6 ebeb JMP 0x45ec93
main.go:7 0x45eca8 e8b3afffff CALL
runtime.morestack_noctxt(SB)
main.go:7 0x45ecad ebb1 JMP main.test(SB)
```
i was confused with the instruction ` main.go:8 0x45ec80 8407
TESTB AL, 0(DI)`
i think it must used for checking nil pointer . but both test and cmp will
modify ZF in eflags. ( there is a cmp instruction follow the test )
i think it should insert instruction `JE 0x45ec9c ` between test and cml
instruction .
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