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cmd/compile: regression passing constants to mapaccess routines #19015

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randall77 opened this issue Feb 9, 2017 · 4 comments
Closed

cmd/compile: regression passing constants to mapaccess routines #19015

randall77 opened this issue Feb 9, 2017 · 4 comments
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FrozenDueToAge Performance
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Go1.9

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@randall77
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func f(m map[int]int) int {
	return m[5]
}

Passing the 5 to mapaccess1_fast64 used to be just a store of 5 to the stack. Now it is a load of 5 from a global constant, then a store of that value to the stack.

In Go 1.8rc3:

	0x001d 00029 (tmp2.go:4)	LEAQ	type.map[int]int(SB), AX
	0x0024 00036 (tmp2.go:4)	MOVQ	AX, (SP)
	0x0028 00040 (tmp2.go:4)	MOVQ	"".m+48(FP), AX
	0x002d 00045 (tmp2.go:4)	MOVQ	AX, 8(SP)
	0x0032 00050 (tmp2.go:4)	MOVQ	$5, 16(SP)
	0x003b 00059 (tmp2.go:4)	PCDATA	$0, $1
	0x003b 00059 (tmp2.go:4)	CALL	runtime.mapaccess1_fast64(SB)

At tip:

	0x001d 00029 (tmp2.go:4)	LEAQ	type.map[int]int(SB), AX
	0x0024 00036 (tmp2.go:4)	MOVQ	AX, (SP)
	0x0028 00040 (tmp2.go:4)	MOVQ	"".m+48(FP), AX
	0x002d 00045 (tmp2.go:4)	MOVQ	AX, 8(SP)
	0x0032 00050 (tmp2.go:4)	MOVQ	"".statictmp_0(SB), AX
	0x0039 00057 (tmp2.go:4)	MOVQ	AX, 16(SP)
	0x003e 00062 (tmp2.go:4)	PCDATA	$0, $1
	0x003e 00062 (tmp2.go:4)	CALL	runtime.mapaccess1_fast64(SB)

@mdempsky
Might be related to #18370.

This issue doesn't seem to occur for regular function calls - we marshal those arguments correctly.
@bradfitz
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bradfitz commented Feb 9, 2017

Or @josharian's 0358367 or c682d32?

@bradfitz bradfitz added this to the Go1.9 milestone Feb 9, 2017
@cherrymui
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It is c682d32, CL https://go-review.googlesource.com/35554. Before this CL, it generates autotmp to make the constant addressable, after this CL it makes statictmp. It seems that we actually don't need to make it addressable though?

@josharian
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Looking into this

@gopherbot
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CL https://golang.org/cl/36693 mentions this issue.

@golang golang locked and limited conversation to collaborators Feb 10, 2018
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