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cmd/compile: racewalk generates too many runtime.racewrite() calls #4332

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dvyukov opened this issue Nov 2, 2012 · 8 comments
Closed

cmd/compile: racewalk generates too many runtime.racewrite() calls #4332

dvyukov opened this issue Nov 2, 2012 · 8 comments
Labels
FrozenDueToAge Performance RaceDetector
Milestone
Unplanned

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@dvyukov
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dvyukov commented Nov 2, 2012 

For the following code
        t := []byte("hello world")
it generates 11 runtime.racewrite. Seemingly for each char in the string. I think we
need to do better.


func Encode() ([]byte, error) {
        t := []byte("hello world")
  400c25:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400c2c:       00 
  400c2d:       48 89 1c 24             mov    %rbx,(%rsp)
  400c31:       e8 2a cc 00 00          callq  40d860 <runtime.racewrite>
  400c36:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400c3d:       00 
  400c3e:       48 ff c3                inc    %rbx
  400c41:       48 89 1c 24             mov    %rbx,(%rsp)
  400c45:       e8 16 cc 00 00          callq  40d860 <runtime.racewrite>
  400c4a:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400c51:       00 
  400c52:       48 83 c3 02             add    $0x2,%rbx
  400c56:       48 89 1c 24             mov    %rbx,(%rsp)
  400c5a:       e8 01 cc 00 00          callq  40d860 <runtime.racewrite>
  400c5f:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400c66:       00 
  400c67:       48 83 c3 03             add    $0x3,%rbx
  400c6b:       48 89 1c 24             mov    %rbx,(%rsp)
  400c6f:       e8 ec cb 00 00          callq  40d860 <runtime.racewrite>
  400c74:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400c7b:       00 
  400c7c:       48 83 c3 04             add    $0x4,%rbx
  400c80:       48 89 1c 24             mov    %rbx,(%rsp)
  400c84:       e8 d7 cb 00 00          callq  40d860 <runtime.racewrite>
  400c89:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400c90:       00 
  400c91:       48 83 c3 05             add    $0x5,%rbx
  400c95:       48 89 1c 24             mov    %rbx,(%rsp)
  400c99:       e8 c2 cb 00 00          callq  40d860 <runtime.racewrite>
  400c9e:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400ca5:       00 
  400ca6:       48 83 c3 06             add    $0x6,%rbx
  400caa:       48 89 1c 24             mov    %rbx,(%rsp)
  400cae:       e8 ad cb 00 00          callq  40d860 <runtime.racewrite>
  400cb3:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400cba:       00 
  400cbb:       48 83 c3 07             add    $0x7,%rbx
  400cbf:       48 89 1c 24             mov    %rbx,(%rsp)
  400cc3:       e8 98 cb 00 00          callq  40d860 <runtime.racewrite>
  400cc8:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400ccf:       00 
  400cd0:       48 83 c3 08             add    $0x8,%rbx
  400cd4:       48 89 1c 24             mov    %rbx,(%rsp)
  400cd8:       e8 83 cb 00 00          callq  40d860 <runtime.racewrite>
  400cdd:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400ce4:       00 
  400ce5:       48 83 c3 09             add    $0x9,%rbx
  400ce9:       48 89 1c 24             mov    %rbx,(%rsp)
  400ced:       e8 6e cb 00 00          callq  40d860 <runtime.racewrite>
  400cf2:       48 8d 1c 25 58 14 43    lea    0x431458,%rbx
  400cf9:       00 
  400cfa:       48 83 c3 0a             add    $0xa,%rbx
  400cfe:       48 89 1c 24             mov    %rbx,(%rsp)
  400d02:       e8 59 cb 00 00          callq  40d860 <runtime.racewrite>
  400d07:       48 c7 04 24 88 76 42    movq   $0x427688,(%rsp)
  400d0e:       00 
  400d0f:       e8 5c 1d 01 00          callq  412a70 <runtime.new>
  400d14:       48 8b 5c 24 08          mov    0x8(%rsp),%rbx
  400d19:       48 89 5c 24 28          mov    %rbx,0x28(%rsp)
  400d1e:       48 8b 5c 24 28          mov    0x28(%rsp),%rbx
  400d23:       48 89 1c 24             mov    %rbx,(%rsp)
  400d27:       e8 34 cb 00 00          callq  40d860 <runtime.racewrite>
  400d2c:       48 8b 7c 24 28          mov    0x28(%rsp),%rdi
  400d31:       48 8d 34 25 58 14 43    lea    0x431458,%rsi
  400d38:       00 
  400d39:       48 a5                   movsq  %ds:(%rsi),%es:(%rdi)
  400d3b:       a4                      movsb  %ds:(%rsi),%es:(%rdi)
  400d3c:       a4                      movsb  %ds:(%rsi),%es:(%rdi)
  400d3d:       a4                      movsb  %ds:(%rsi),%es:(%rdi)
  400d3e:       48 8d 5c 24 10          lea    0x10(%rsp),%rbx
  400d43:       48 89 1c 24             mov    %rbx,(%rsp)
  400d47:       e8 14 cb 00 00          callq  40d860 <runtime.racewrite>
  400d4c:       48 c7 44 24 18 0b 00    movq   $0xb,0x18(%rsp)
  400d53:       00 00 
  400d55:       48 c7 44 24 20 0b 00    movq   $0xb,0x20(%rsp)
  400d5c:       00 00 
  400d5e:       48 8b 5c 24 28          mov    0x28(%rsp),%rbx
  400d63:       48 89 5c 24 10          mov    %rbx,0x10(%rsp)
/tmp/test.go:5
        return t, nil
  400d68:       48 8d 5c 24 38          lea    0x38(%rsp),%rbx
  400d6d:       48 89 1c 24             mov    %rbx,(%rsp)
  400d71:       e8 ea ca 00 00          callq  40d860 <runtime.racewrite>
  400d76:       48 8d 5c 24 10          lea    0x10(%rsp),%rbx
  400d7b:       48 89 1c 24             mov    %rbx,(%rsp)
  400d7f:       e8 6c cb 00 00          callq  40d8f0 <runtime.raceread>
  400d84:       48 8b 5c 24 10          mov    0x10(%rsp),%rbx
  400d89:       48 89 5c 24 38          mov    %rbx,0x38(%rsp)
  400d8e:       48 8b 5c 24 18          mov    0x18(%rsp),%rbx
  400d93:       48 89 5c 24 40          mov    %rbx,0x40(%rsp)
  400d98:       48 8b 5c 24 20          mov    0x20(%rsp),%rbx
  400d9d:       48 89 5c 24 48          mov    %rbx,0x48(%rsp)
  400da2:       48 c7 44 24 50 00 00    movq   $0x0,0x50(%rsp)
  400da9:       00 00 
  400dab:       48 c7 44 24 58 00 00    movq   $0x0,0x58(%rsp)
  400db2:       00 00 
  400db4:       e8 57 cc 00 00          callq  40da10 <runtime.racefuncexit>
/tmp/test.go:6
}
  400db9:       48 83 c4 30             add    $0x30,%rsp
  400dbd:       c3                      retq
@remyoudompheng
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Comment 1:

Is this the same as issue #4250 ?

@dvyukov
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dvyukov commented Nov 2, 2012

Comment 2:

4250 is for runtime library and operations like slicecopy.
This one is for compiler instrumentation. If the compiler generates 100 separate call,
there is nothing runtime can do.

@dvyukov
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dvyukov commented Jan 8, 2013

Comment 3:

Labels changed: added performance.

@robpike
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robpike commented Mar 7, 2013

Comment 4:

Labels changed: removed go1.1maybe.

@rsc
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rsc commented Nov 27, 2013

Comment 5:

Labels changed: added go1.3maybe.

@rsc
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rsc commented Dec 4, 2013

Comment 6:

Labels changed: added release-none, removed go1.3maybe.

@rsc
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rsc commented Dec 4, 2013

Comment 7:

Labels changed: added repo-main.

@rsc rsc added this to the Unplanned milestone Apr 10, 2015
@rsc rsc changed the title cmd/gc: racewalk generates too many runtime.racewrite() calls cmd/compile: racewalk generates too many runtime.racewrite() calls Jun 8, 2015
@josharian
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package p

func f() {
	t := []byte("hello world")
	_ = t
}

now compiles to:

"".f STEXT size=100 args=0x0 locals=0x58
	0x0000 00000 (x.go:3)	TEXT	"".f(SB), $88-0
	0x0000 00000 (x.go:3)	MOVQ	(TLS), CX
	0x0009 00009 (x.go:3)	CMPQ	SP, 16(CX)
	0x000d 00013 (x.go:3)	JLS	93
	0x000f 00015 (x.go:3)	SUBQ	$88, SP
	0x0013 00019 (x.go:3)	MOVQ	BP, 80(SP)
	0x0018 00024 (x.go:3)	LEAQ	80(SP), BP
	0x001d 00029 (x.go:3)	FUNCDATA	$0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x001d 00029 (x.go:3)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x001d 00029 (x.go:3)	MOVQ	""..fp+88(SP), AX
	0x0022 00034 (x.go:5)	MOVQ	AX, (SP)
	0x0026 00038 (x.go:5)	PCDATA	$0, $0
	0x0026 00038 (x.go:5)	CALL	runtime.racefuncenter(SB)
	0x002b 00043 (x.go:5)	LEAQ	""..autotmp_2+48(SP), AX
	0x0030 00048 (x.go:4)	MOVQ	AX, (SP)
	0x0034 00052 (x.go:4)	LEAQ	go.string."hello world"(SB), AX
	0x003b 00059 (x.go:4)	MOVQ	AX, 8(SP)
	0x0040 00064 (x.go:4)	MOVQ	$11, 16(SP)
	0x0049 00073 (x.go:4)	PCDATA	$0, $0
	0x0049 00073 (x.go:4)	CALL	runtime.stringtoslicebyte(SB)
	0x004e 00078 (x.go:5)	PCDATA	$0, $0
	0x004e 00078 (x.go:5)	CALL	runtime.racefuncexit(SB)
	0x0053 00083 (x.go:6)	MOVQ	80(SP), BP
	0x0058 00088 (x.go:6)	ADDQ	$88, SP
	0x005c 00092 (x.go:6)	RET
	0x005d 00093 (x.go:6)	NOP
	0x005d 00093 (x.go:3)	PCDATA	$0, $-1
	0x005d 00093 (x.go:3)	CALL	runtime.morestack_noctxt(SB)
	0x0062 00098 (x.go:3)	JMP	0

Calling this fixed. If we find cases other than converting a byte slice to a string, we can open new issues for them.

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@josharian @rsc @remyoudompheng @dvyukov @robpike @gopherbot