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| author | Matthew Dempsky <mdempsky@google.com> | 2013-01-18 17:29:53 -0500 |
|---|---|---|
| committer | Matthew Dempsky <mdempsky@google.com> | 2013-01-18 17:29:53 -0500 |
| commit | df1ad20b3f949ac7154133b10ed2b8c230a2678b (patch) | |
| tree | 7215dd8ce776e0ec08c5d3273607219c74bd68af /src/cmd/8c/txt.c | |
| parent | 431793477499ec24686b519cb427c3ff7ba7b4bc (diff) | |
| download | go-df1ad20b3f949ac7154133b10ed2b8c230a2678b.tar.gz | |
cmd/6c: Optimize rotate expressions to use rotate instructions.
For simplicity, only recognizes expressions of the exact form
"(x << a) | (x >> b)" where x is a variable and a and b are
integer constant expressions that add to x's bit width.
Fixes issue 4629.
$ cat rotate.c
unsigned int
rotate(unsigned int x)
{
x = (x << 3) | (x >> (sizeof(x) * 8 - 3));
return x;
}
## BEFORE
$ go tool 6c -S rotate.c
(rotate.c:2) TEXT rotate+0(SB),$0-8
(rotate.c:2) MOVL x+0(FP),!!DX
(rotate.c:4) MOVL DX,!!AX
(rotate.c:4) SALL $3,!!AX
(rotate.c:4) MOVL DX,!!CX
(rotate.c:4) SHRL $29,!!CX
(rotate.c:4) ORL CX,!!AX
(rotate.c:5) RET ,!!
(rotate.c:5) RET ,!!
(rotate.c:5) END ,!!
## AFTER
$ go tool 6c -S rotate.c
(rotate.c:2) TEXT rotate+0(SB),$0-8
(rotate.c:4) MOVL x+0(FP),!!AX
(rotate.c:4) ROLL $3,!!AX
(rotate.c:5) RET ,!!
(rotate.c:5) RET ,!!
(rotate.c:5) END ,!!
R=rsc, minux.ma
CC=golang-dev
https://codereview.appspot.com/7069056
Committer: Russ Cox <rsc@golang.org>
Diffstat (limited to 'src/cmd/8c/txt.c')
| -rw-r--r-- | src/cmd/8c/txt.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/cmd/8c/txt.c b/src/cmd/8c/txt.c index d229462da..d7873e385 100644 --- a/src/cmd/8c/txt.c +++ b/src/cmd/8c/txt.c @@ -1253,6 +1253,14 @@ gopcode(int o, Type *ty, Node *f, Node *t) a = ASALW; break; + case OROTL: + a = AROLL; + if(et == TCHAR || et == TUCHAR) + a = AROLB; + if(et == TSHORT || et == TUSHORT) + a = AROLW; + break; + case OFUNC: a = ACALL; break; |