code review 6489067: cmd/8g: import componentgen from 6g.

cmd/8g: import componentgen from 6g.

This makes the compilers code more similar and improves
code generation a lot.

The number of LEAL instructions generated for cmd/go drops
by 60%.

% GOARCH=386 go build -gcflags -S -a cmd/go | grep LEAL | wc -l
Before:       89774
After:        47548

benchmark                              old ns/op    new ns/op    delta
BenchmarkAppendFloatDecimal                  540          444  -17.78%
BenchmarkAppendFloat                        1160         1035  -10.78%
BenchmarkAppendFloatExp                     1060          922  -13.02%
BenchmarkAppendFloatNegExp                  1053          920  -12.63%
BenchmarkAppendFloatBig                     1773         1558  -12.13%
BenchmarkFormatInt                         13065        12481   -4.47%
BenchmarkAppendInt                         10981         9900   -9.84%
BenchmarkFormatUint                         3804         3650   -4.05%
BenchmarkAppendUint                         3506         3303   -5.79%
BenchmarkUnquoteEasy                         714          683   -4.34%
BenchmarkUnquoteHard                        5117         2915  -43.03%

Update issue 1914.

[remyoudompheng, 2012-09-02 08:19:53]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com,
remy@archlinux.org),

I'd like you to review this change to
https://go.googlecode.com/hg/

[remyoudompheng, 2012-09-02 08:21:30]

Making the igen tweak on 6g also reduces the number of LEAQ  (situation
described in 1914), but the LEAQ xx(SP) instances that are eliminating are
mainly assignment of function call arguments, which do not affect
registerization.

[remyoudompheng, 2012-09-02 10:25:59]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com,
remy@archlinux.org),

Please take another look.

[remyoudompheng, 2012-09-02 10:27:26]

Added the similar use of componentgen for zeroing. The number of LEAL in cmd/go
is down to 35724 from 38802. Impact on stack size and performance is sometimes
positive, sometime negative.

[remyoudompheng, 2012-09-05 23:06:24]

Ping.

[nigeltao, 2012-09-07 07:51:41]

https://codereview.appspot.com/6489067/diff/8002/src/cmd/8g/cgen.c
File src/cmd/8g/cgen.c (right):

https://codereview.appspot.com/6489067/diff/8002/src/cmd/8g/cgen.c#newcode781
src/cmd/8g/cgen.c:781: case OINDREG:
6g's igen doesn't do this. Should the "igen is tweaked to be
a no-op on INDREG registers" be a separate change, applied to both 6g and 8g?

[remyoudompheng, 2012-09-07 17:34:24]

On 2012/09/07 07:51:41, nigeltao wrote:
> 6g's igen doesn't do this. Should the "igen is tweaked to be
> a no-op on INDREG registers" be a separate change, applied to both 6g and 8g?

Indeed it would be more logical. Any opinion on this? rsc?

[remyoudompheng, 2012-09-09 08:04:32]

Hello nigeltao@golang.org, rsc@golang.org, golang-dev@googlegroups.com (cc:
golang-dev@googlegroups.com, remy@archlinux.org),

Please take another look.

[nigeltao, 2012-09-09 09:44:39]

LGTM.

Please delete the "Additionnally, igen is tweaked to be
a no-op on INDREG registers." line from the CL description.

Also, updated LEAL count and benchmark numbers in the CL description would be
nice, but don't worry about it if it's too much effort to regenerate.

[remyoudompheng, 2012-09-09 18:21:16]

Updated the description and added "Update issue 1914."

http://codereview.appspot.com/6489067/diff/8002/src/cmd/8g/cgen.c
File src/cmd/8g/cgen.c (right):

http://codereview.appspot.com/6489067/diff/8002/src/cmd/8g/cgen.c#newcode781
src/cmd/8g/cgen.c:781: case OINDREG:
On 2012/09/07 07:51:42, nigeltao wrote:
> 6g's igen doesn't do this. Should the "igen is tweaked to be
> a no-op on INDREG registers" be a separate change, applied to both 6g and 8g?

Done. http://codereview.appspot.com/6494107/

[remyoudompheng, 2012-09-09 18:30:32]

*** Submitted as http://code.google.com/p/go/source/detail?r=9f6681feef6d ***

cmd/8g: import componentgen from 6g.

This makes the compilers code more similar and improves
code generation a lot.

The number of LEAL instructions generated for cmd/go drops
by 60%.

% GOARCH=386 go build -gcflags -S -a cmd/go | grep LEAL | wc -l
Before:       89774
After:        47548

benchmark                              old ns/op    new ns/op    delta
BenchmarkAppendFloatDecimal                  540          444  -17.78%
BenchmarkAppendFloat                        1160         1035  -10.78%
BenchmarkAppendFloatExp                     1060          922  -13.02%
BenchmarkAppendFloatNegExp                  1053          920  -12.63%
BenchmarkAppendFloatBig                     1773         1558  -12.13%
BenchmarkFormatInt                         13065        12481   -4.47%
BenchmarkAppendInt                         10981         9900   -9.84%
BenchmarkFormatUint                         3804         3650   -4.05%
BenchmarkAppendUint                         3506         3303   -5.79%
BenchmarkUnquoteEasy                         714          683   -4.34%
BenchmarkUnquoteHard                        5117         2915  -43.03%

Update issue 1914.

R=nigeltao, rsc, golang-dev
CC=golang-dev, remy
http://codereview.appspot.com/6489067