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cmd/compile: concurrent compilation of generated functions generates an extra nil check #20242

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josharian opened this issue May 4, 2017 · 1 comment
Closed

cmd/compile: concurrent compilation of generated functions generates an extra nil check #20242

josharian opened this issue May 4, 2017 · 1 comment
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Go1.9

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@josharian
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This issue assumes CL 41503 has gone in.

package main

func f(...interface{}) {}

func main() {
	f(1, 2)
}

With -c, the generated code contains an extra nil check.

Before:

type..hash.[2]interface {} STEXT dupok size=110 args=0x18 locals=0x28
	0x0000 00000 (<autogenerated>:1)	TEXT	type..hash.[2]interface {}(SB), DUPOK, $40-24
	0x0000 00000 (<autogenerated>:1)	MOVQ	(TLS), CX
	0x0009 00009 (<autogenerated>:1)	CMPQ	SP, 16(CX)
	0x000d 00013 (<autogenerated>:1)	JLS	103
	0x000f 00015 (<autogenerated>:1)	SUBQ	$40, SP
	0x0013 00019 (<autogenerated>:1)	MOVQ	BP, 32(SP)
	0x0018 00024 (<autogenerated>:1)	LEAQ	32(SP), BP
	0x001d 00029 (<autogenerated>:1)	FUNCDATA	$0, gclocals·d4dc2f11db048877dbc0f60a22b4adb3(SB)
	0x001d 00029 (<autogenerated>:1)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x001d 00029 (<autogenerated>:1)	MOVL	$0, AX
	0x001f 00031 (<autogenerated>:1)	MOVQ	"".h+56(SP), CX
	0x0024 00036 (<autogenerated>:1)	JMP	82
	0x0026 00038 (<autogenerated>:1)	MOVQ	AX, "".i+24(SP)
	0x002b 00043 (<autogenerated>:1)	SHLQ	$4, AX
	0x002f 00047 (<autogenerated>:1)	MOVQ	"".p+48(SP), BX
	0x0034 00052 (<autogenerated>:1)	ADDQ	BX, AX
	0x0037 00055 (<autogenerated>:1)	MOVQ	AX, (SP)
	0x003b 00059 (<autogenerated>:1)	MOVQ	CX, 8(SP)
	0x0040 00064 (<autogenerated>:1)	PCDATA	$0, $0
	0x0040 00064 (<autogenerated>:1)	CALL	runtime.nilinterhash(SB)
	0x0045 00069 (<autogenerated>:1)	MOVQ	16(SP), CX
	0x004a 00074 (<autogenerated>:1)	MOVQ	"".i+24(SP), AX
	0x004f 00079 (<autogenerated>:1)	INCQ	AX
	0x0052 00082 (<autogenerated>:1)	CMPQ	AX, $2
	0x0056 00086 (<autogenerated>:1)	JLT	38
	0x0058 00088 (<autogenerated>:1)	MOVQ	CX, "".~r2+64(SP)
	0x005d 00093 (<autogenerated>:1)	MOVQ	32(SP), BP
	0x0062 00098 (<autogenerated>:1)	ADDQ	$40, SP
	0x0066 00102 (<autogenerated>:1)	RET
	0x0067 00103 (<autogenerated>:1)	NOP
	0x0067 00103 (<autogenerated>:1)	PCDATA	$0, $-1
	0x0067 00103 (<autogenerated>:1)	CALL	runtime.morestack_noctxt(SB)
	0x006c 00108 (<autogenerated>:1)	JMP	0

After:

type..hash.[2]interface {} STEXT dupok size=112 args=0x18 locals=0x28
	0x0000 00000 (<autogenerated>:1)	TEXT	type..hash.[2]interface {}(SB), DUPOK, $40-24
	0x0000 00000 (<autogenerated>:1)	MOVQ	(TLS), CX
	0x0009 00009 (<autogenerated>:1)	CMPQ	SP, 16(CX)
	0x000d 00013 (<autogenerated>:1)	JLS	105
	0x000f 00015 (<autogenerated>:1)	SUBQ	$40, SP
	0x0013 00019 (<autogenerated>:1)	MOVQ	BP, 32(SP)
	0x0018 00024 (<autogenerated>:1)	LEAQ	32(SP), BP
	0x001d 00029 (<autogenerated>:1)	FUNCDATA	$0, gclocals·d4dc2f11db048877dbc0f60a22b4adb3(SB)
	0x001d 00029 (<autogenerated>:1)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x001d 00029 (<autogenerated>:1)	MOVL	$0, AX
	0x001f 00031 (<autogenerated>:1)	MOVQ	"".h+56(SP), CX
	0x0024 00036 (<autogenerated>:1)	JMP	84
	0x0026 00038 (<autogenerated>:1)	MOVQ	AX, "".i+24(SP)
	0x002b 00043 (<autogenerated>:1)	MOVQ	"".p+48(SP), DX
	0x0030 00048 (<autogenerated>:1)	TESTB	AL, (DX)
	0x0032 00050 (<autogenerated>:1)	SHLQ	$4, AX
	0x0036 00054 (<autogenerated>:1)	ADDQ	DX, AX
	0x0039 00057 (<autogenerated>:1)	MOVQ	AX, (SP)
	0x003d 00061 (<autogenerated>:1)	MOVQ	CX, 8(SP)
	0x0042 00066 (<autogenerated>:1)	PCDATA	$0, $0
	0x0042 00066 (<autogenerated>:1)	CALL	runtime.nilinterhash(SB)
	0x0047 00071 (<autogenerated>:1)	MOVQ	16(SP), CX
	0x004c 00076 (<autogenerated>:1)	MOVQ	"".i+24(SP), AX
	0x0051 00081 (<autogenerated>:1)	INCQ	AX
	0x0054 00084 (<autogenerated>:1)	CMPQ	AX, $2
	0x0058 00088 (<autogenerated>:1)	JLT	38
	0x005a 00090 (<autogenerated>:1)	MOVQ	CX, "".~r2+64(SP)
	0x005f 00095 (<autogenerated>:1)	MOVQ	32(SP), BP
	0x0064 00100 (<autogenerated>:1)	ADDQ	$40, SP
	0x0068 00104 (<autogenerated>:1)	RET
	0x0069 00105 (<autogenerated>:1)	NOP
	0x0069 00105 (<autogenerated>:1)	PCDATA	$0, $-1
	0x0069 00105 (<autogenerated>:1)	CALL	runtime.morestack_noctxt(SB)
	0x006e 00110 (<autogenerated>:1)	JMP	0

But the -c flag must produce identical output.

Found by go-fuzz.
@josharian josharian added this to the Go1.9 milestone May 4, 2017
@josharian josharian self-assigned this May 4, 2017
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CL https://golang.org/cl/42591 mentions this issue.

@golang golang locked and limited conversation to collaborators May 5, 2018
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