code review 6209077: cmd/gc: faster code, mainly for rotate

cmd/gc: faster code, mainly for rotate

* Eliminate bounds check on known small shifts.
* Rewrite x<<s | x>>(32-s) as a rotate (constant s).
* More aggressive (but still minimal) range analysis.

[rsc, 2012-05-18 00:27:06]

Hello ken2 (cc: golang-dev@googlegroups.com),

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

[dave_cheney.net, 2012-05-18 04:42:16]

Hi Russ,

There is a compile error under clang-3.0.

pando(~/go/src) % export CC=clang
pando(~/go/src) % ./all.bash
# Building C bootstrap tool.
cmd/dist

# Building compilers and Go bootstrap tool for host, linux/arm.
lib9
libbio
libmach
misc/pprof
cmd/addr2line
cmd/cov
cmd/nm
cmd/objdump
cmd/pack
cmd/prof
cmd/cc
cmd/gc
/home/dfc/go/src/cmd/gc/walk.c:870:8: error: self-comparison always evaluates to
false [-Werror,-Wtautological-compare]
                if(t != t && isptr[t->etype])
                     ^
1 error generated.
go tool dist: FAILED: clang -Wall -Wno-sign-compare -Wno-missing-braces
-Wno-parentheses -Wno-unknown-pragmas -Wno-switch -Wno-comment -Werror
-fno-common -ggdb -O2 -Wno-dangling-else -Wno-unused-value -c -I
/home/dfc/go/include -I /home/dfc/go/src/cmd/gc -o $WORK/walk.o
/home/dfc/go/src/cmd/gc/walk.c

[iant2, 2012-05-18 05:51:01]

dave@cheney.net writes:

> /home/dfc/go/src/cmd/gc/walk.c:870:8: error: self-comparison always
> evaluates to false [-Werror,-Wtautological-compare]
>                 if(t != t && isptr[t->etype])

Should be t != T.

Ian

[dave_cheney.net, 2012-05-18 06:03:59]

Thanks Ian,

Now I'm getting another error on crypto/sha512.

pando(~/go/src) % go build -x crypto/sha512
WORK=/tmp/go-build170658554
mkdir -p $WORK/crypto/sha512/_obj/
cd /home/dfc/go/src/pkg/crypto/sha512
/home/dfc/go/pkg/tool/linux_arm/5g -o $WORK/crypto/sha512/_obj/_go_.5
-p crypto/sha512 -D _/home/dfc/go/src/pkg/crypto/sha512 -I $WORK
./sha512.go ./sha512block.go
# crypto/sha512
pkg/crypto/sha512/sha512block.go:115: internal compiler error: cgen64 LROT

On Fri, May 18, 2012 at 3:50 PM, Ian Lance Taylor <iant@google.com> wrote:
> dave@cheney.net writes:
>
>> /home/dfc/go/src/cmd/gc/walk.c:870:8: error: self-comparison always
>> evaluates to false [-Werror,-Wtautological-compare]
>>                 if(t != t && isptr[t->etype])
>
> Should be t != T.
>
> Ian

[rsc, 2012-05-24 21:20:12]

*** Submitted as http://code.google.com/p/go/source/detail?r=67c0b8c8fb29 ***

cmd/gc: faster code, mainly for rotate

* Eliminate bounds check on known small shifts.
* Rewrite x<<s | x>>(32-s) as a rotate (constant s).
* More aggressive (but still minimal) range analysis.

R=ken, dave, iant
CC=golang-dev
http://codereview.appspot.com/6209077

[remyoudompheng, 2012-05-25 00:01:02]

Impressive: (Core 2 Quad 2.33 GHz)

crypto/md5
benchmark           old MB/s     new MB/s  speedup
BenchmarkHash1K       190.89       266.47    1.40x
BenchmarkHash8K       196.35       289.04    1.47x

[rsc, 2012-05-25 02:28:02]

On Thu, May 24, 2012 at 8:01 PM,  <remyoudompheng@gmail.com> wrote:
> Impressive: (Core 2 Quad 2.33 GHz)
>
> crypto/md5
> benchmark           old MB/s     new MB/s  speedup
> BenchmarkHash1K       190.89       266.47    1.40x
> BenchmarkHash8K       196.35       289.04    1.47x

This 1.4x was included in the 3x the earlier CL was claiming.

Russ