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Russ Cox d447279927 cmd/internal/gc: optimize slice + write barrier 
The code generated for a slice x[i:j] or x[i:j:k] computes the entire
new slice (base, len, cap) and then uses it as the evaluation of the
slice expression.

If the slice is part of an update x = x[i:j] or x = x[i:j:k], there are
opportunities to avoid computing some of these fields.

For x = x[0:i], we know that only the len is changing;
base can be ignored completely, and cap can be left unmodified.

For x = x[0:i:j], we know that only len and cap are changing;
base can be ignored completely.

For x = x[i:i], we know that the resulting cap is zero, and we don't
adjust the base during a slice producing a zero-cap result,
so again base can be ignored completely.

No write to base, no write barrier.

The old slice code was trying to work at a Go syntax level, mainly
because that was how you wrote code just once instead of once
per architecture. Now the compiler is factored a bit better and we
can implement slice during code generation but still have one copy
of the code. So the new code is working at that lower level.
(It must, to update only parts of the result.)

This CL by itself:
name                   old mean              new mean              delta
BinaryTree17            5.81s × (0.98,1.03)   5.71s × (0.96,1.05)     ~    (p=0.101)
Fannkuch11              4.35s × (1.00,1.00)   4.39s × (1.00,1.00)   +0.79% (p=0.000)
FmtFprintfEmpty        86.0ns × (0.94,1.11)  82.6ns × (0.98,1.04)   -3.86% (p=0.048)
FmtFprintfString        276ns × (0.98,1.04)   273ns × (0.98,1.02)     ~    (p=0.235)
FmtFprintfInt           274ns × (0.98,1.06)   270ns × (0.99,1.01)     ~    (p=0.119)
FmtFprintfIntInt        506ns × (0.99,1.01)   475ns × (0.99,1.01)   -6.02% (p=0.000)
FmtFprintfPrefixedInt   391ns × (0.99,1.01)   393ns × (1.00,1.01)     ~    (p=0.139)
FmtFprintfFloat         566ns × (0.99,1.01)   574ns × (1.00,1.01)   +1.33% (p=0.001)
FmtManyArgs            1.91µs × (0.99,1.01)  1.87µs × (0.99,1.02)   -1.83% (p=0.000)
GobDecode              15.3ms × (0.99,1.02)  15.0ms × (0.98,1.05)   -1.84% (p=0.042)
GobEncode              11.5ms × (0.97,1.03)  11.4ms × (0.99,1.03)     ~    (p=0.152)
Gzip                    645ms × (0.99,1.01)   647ms × (0.99,1.01)     ~    (p=0.265)
Gunzip                  142ms × (1.00,1.00)   143ms × (1.00,1.01)   +0.90% (p=0.000)
HTTPClientServer       90.5µs × (0.97,1.04)  88.5µs × (0.99,1.03)   -2.27% (p=0.014)
JSONEncode             32.0ms × (0.98,1.03)  29.6ms × (0.98,1.01)   -7.51% (p=0.000)
JSONDecode              114ms × (0.99,1.01)   104ms × (1.00,1.01)   -8.60% (p=0.000)
Mandelbrot200          6.04ms × (1.00,1.01)  6.02ms × (1.00,1.00)     ~    (p=0.057)
GoParse                6.47ms × (0.97,1.05)  6.37ms × (0.97,1.04)     ~    (p=0.105)
RegexpMatchEasy0_32     171ns × (0.93,1.07)   152ns × (0.99,1.01)  -11.09% (p=0.000)
RegexpMatchEasy0_1K     550ns × (0.98,1.01)   530ns × (1.00,1.00)   -3.78% (p=0.000)
RegexpMatchEasy1_32     135ns × (0.99,1.02)   134ns × (0.99,1.01)   -1.33% (p=0.002)
RegexpMatchEasy1_1K     879ns × (1.00,1.01)   865ns × (1.00,1.00)   -1.58% (p=0.000)
RegexpMatchMedium_32    243ns × (1.00,1.00)   233ns × (1.00,1.00)   -4.30% (p=0.000)
RegexpMatchMedium_1K   70.3µs × (1.00,1.00)  69.5µs × (1.00,1.00)   -1.13% (p=0.000)
RegexpMatchHard_32     3.82µs × (1.00,1.01)  3.74µs × (1.00,1.00)   -1.95% (p=0.000)
RegexpMatchHard_1K      117µs × (1.00,1.00)   115µs × (1.00,1.00)   -1.69% (p=0.000)
Revcomp                 917ms × (0.97,1.04)   920ms × (0.97,1.04)     ~    (p=0.786)
Template                114ms × (0.99,1.01)   117ms × (0.99,1.01)   +2.58% (p=0.000)
TimeParse               622ns × (0.99,1.01)   615ns × (0.99,1.00)   -1.06% (p=0.000)
TimeFormat              665ns × (0.99,1.01)   654ns × (0.99,1.00)   -1.70% (p=0.000)

This CL and previous CL (append) combined:
name                   old mean              new mean              delta
BinaryTree17            5.68s × (0.97,1.04)   5.71s × (0.96,1.05)     ~    (p=0.638)
Fannkuch11              4.41s × (0.98,1.03)   4.39s × (1.00,1.00)     ~    (p=0.474)
FmtFprintfEmpty        92.7ns × (0.91,1.16)  82.6ns × (0.98,1.04)  -10.89% (p=0.004)
FmtFprintfString        281ns × (0.96,1.08)   273ns × (0.98,1.02)     ~    (p=0.078)
FmtFprintfInt           288ns × (0.97,1.06)   270ns × (0.99,1.01)   -6.37% (p=0.000)
FmtFprintfIntInt        493ns × (0.97,1.04)   475ns × (0.99,1.01)   -3.53% (p=0.002)
FmtFprintfPrefixedInt   423ns × (0.97,1.04)   393ns × (1.00,1.01)   -7.07% (p=0.000)
FmtFprintfFloat         598ns × (0.99,1.01)   574ns × (1.00,1.01)   -4.02% (p=0.000)
FmtManyArgs            1.89µs × (0.98,1.05)  1.87µs × (0.99,1.02)     ~    (p=0.305)
GobDecode              14.8ms × (0.98,1.03)  15.0ms × (0.98,1.05)     ~    (p=0.237)
GobEncode              12.3ms × (0.98,1.01)  11.4ms × (0.99,1.03)   -6.95% (p=0.000)
Gzip                    656ms × (0.99,1.05)   647ms × (0.99,1.01)     ~    (p=0.101)
Gunzip                  142ms × (1.00,1.00)   143ms × (1.00,1.01)   +0.58% (p=0.001)
HTTPClientServer       91.2µs × (0.97,1.04)  88.5µs × (0.99,1.03)   -3.02% (p=0.003)
JSONEncode             32.6ms × (0.97,1.08)  29.6ms × (0.98,1.01)   -9.10% (p=0.000)
JSONDecode              114ms × (0.97,1.05)   104ms × (1.00,1.01)   -8.74% (p=0.000)
Mandelbrot200          6.11ms × (0.98,1.04)  6.02ms × (1.00,1.00)     ~    (p=0.090)
GoParse                6.66ms × (0.97,1.04)  6.37ms × (0.97,1.04)   -4.41% (p=0.000)
RegexpMatchEasy0_32     159ns × (0.99,1.00)   152ns × (0.99,1.01)   -4.69% (p=0.000)
RegexpMatchEasy0_1K     538ns × (1.00,1.01)   530ns × (1.00,1.00)   -1.57% (p=0.000)
RegexpMatchEasy1_32     138ns × (1.00,1.00)   134ns × (0.99,1.01)   -2.91% (p=0.000)
RegexpMatchEasy1_1K     869ns × (0.99,1.01)   865ns × (1.00,1.00)   -0.51% (p=0.012)
RegexpMatchMedium_32    252ns × (0.99,1.01)   233ns × (1.00,1.00)   -7.85% (p=0.000)
RegexpMatchMedium_1K   72.7µs × (1.00,1.00)  69.5µs × (1.00,1.00)   -4.43% (p=0.000)
RegexpMatchHard_32     3.85µs × (1.00,1.00)  3.74µs × (1.00,1.00)   -2.74% (p=0.000)
RegexpMatchHard_1K      118µs × (1.00,1.00)   115µs × (1.00,1.00)   -2.24% (p=0.000)
Revcomp                 920ms × (0.97,1.07)   920ms × (0.97,1.04)     ~    (p=0.998)
Template                129ms × (0.98,1.03)   117ms × (0.99,1.01)   -9.79% (p=0.000)
TimeParse               619ns × (0.99,1.01)   615ns × (0.99,1.00)   -0.57% (p=0.011)
TimeFormat              661ns × (0.98,1.04)   654ns × (0.99,1.00)     ~    (p=0.223)

Change-Id: If054d81ab2c71d8d62cf54b5b1fac2af66b387fc
Reviewed-on: https://go-review.googlesource.com/9813
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2015-05-13 19:20:39 +00:00
api runtime: remove unused GC times from api.next 2015-05-06 14:49:26 +00:00
doc spec: fix binary expression grammar rule 2015-05-13 17:40:38 +00:00
lib/time remove the obsolete lib/codereview. 2014-12-08 07:51:54 +00:00
misc misc/cgo/testcshared: fix test for android. 2015-05-12 23:46:33 +00:00
src cmd/internal/gc: optimize slice + write barrier 2015-05-13 19:20:39 +00:00
test cmd/internal/gc: optimize slice + write barrier 2015-05-13 19:20:39 +00:00
.gitattributes .gitattributes: prevent all magic line ending changes 2014-12-12 23:14:54 +00:00
.gitignore .gitignore: ignore ARM64 build products 2015-03-16 18:44:22 +00:00
AUTHORS A+C: add another email address for Emil Hessman 2014-11-12 10:01:23 -08:00
CONTRIBUTING.md doc: direct people to the mailing list 2015-01-18 21:27:07 +00:00
CONTRIBUTORS CONTRIBUTORS: add Burcu Dogan's personal mail 2015-05-06 16:06:42 +00:00
favicon.ico godoc: update favicon 2012-10-11 17:02:36 +11:00
LICENSE
PATENTS
README.md doc: fix broken link in README 2015-02-19 05:50:57 +00:00
robots.txt

README.md

The Go Programming Language

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Binary Distribution Notes

If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.

For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:

export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin

See https://golang.org/doc/install or doc/install.html for more details.