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cmd/gc: recognize (a.b[0]<<1 | a.b[0]>>31) as a rotate, not just 

(x<<1 | x>>31).

Fixes #5084.

On the SHA3 benchmark proposals at
https://golang.org/cl/7760044/

benchmark                       old ns/op    new ns/op    delta
BenchmarkPermutationFunction         1288         1191   -7.53%
BenchmarkSingleByteWrite             5795         5811   +0.28%
BenchmarkBlockWrite512                178          179   +0.56%
BenchmarkBlockWrite384                230          233   +1.30%
BenchmarkBlockWrite256                282          286   +1.42%
BenchmarkBlockWrite224                301          306   +1.66%
BenchmarkBulkHashSHA3_512          326885       304548   -6.83%
BenchmarkBulkHashSHA3_384          234839       220074   -6.29%
BenchmarkBulkHashSHA3_256          186969       175790   -5.98%
BenchmarkBulkHashSHA3_224          178133       167489   -5.98%

For a function like

func g() {
        x = a[3]<<20 | a[3]>>12
}

the asm goes from

0006 (main.go:10) TEXT    g+0(SB),$0-0
0007 (main.go:10) MOVL    a+12(SB),BP
0008 (main.go:10) LOCALS  ,$0
0009 (main.go:11) MOVL    BP,BX
0010 (main.go:11) SHLL    $20,BX
0011 (main.go:11) SHRL    $12,BP
0012 (main.go:11) ORL     BP,BX
0013 (main.go:11) MOVL    BX,x+0(SB)
0014 (main.go:12) RET     ,

to

0006 (main.go:10) TEXT    g+0(SB),$0-0
0007 (main.go:10) LOCALS  ,$0
0008 (main.go:11) MOVL    a+12(SB),BX
0009 (main.go:11) ROLL    $20,BX
0010 (main.go:11) MOVL    BX,x+0(SB)
0011 (main.go:12) RET     ,

R=rsc, iant, remyoudompheng
CC=golang-dev, jcb
https://golang.org/cl/7944043
This commit is contained in:
Nigel Tao 2013-04-02 21:14:34 +11:00
parent 54faecac0b
commit 4de6687554
1 changed files with 23 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
src/cmd/gc/walk.c
View File

@ -2897,14 +2897,29 @@ hard:
static int
samecheap(Node *a, Node *b)
{
if(a == N || b == N || a->op != b->op)
return 0;
switch(a->op) {
case ONAME:
return a == b;
// TODO: Could do more here, but maybe this is enough.
// It's all cheapexpr does.
Node *ar, *br;
while(a != N && b != N && a->op == b->op) {
switch(a->op) {
default:
return 0;
case ONAME:
return a == b;
case ODOT:
case ODOTPTR:
ar = a->right;
br = b->right;
if(ar->op != ONAME || br->op != ONAME || ar->sym != br->sym)
return 0;
break;
case OINDEX:
ar = a->right;
br = b->right;
if(!isconst(ar, CTINT) || !isconst(br, CTINT) || mpcmpfixfix(ar->val.u.xval, br->val.u.xval) != 0)
return 0;
break;
}
a = a->left;
b = b->left;
}
return 0;
}