code review 6999043: cmd/8g: introduce temporaries in byte multiplication.

cmd/8g: introduce temporaries in byte multiplication.

Also restore the smallintconst case for binary ops.

Fixes issue 3835.

[remyoudompheng, 2012-12-20 23:49:50]

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

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

[DMorsing, 2012-12-21 07:26:51]

Got any before and after assembly comparisons?

[rsc, 2012-12-21 21:21:36]

LGTM

https://codereview.appspot.com/6999043/diff/5001/src/cmd/8g/cgen.c
File src/cmd/8g/cgen.c (right):

https://codereview.appspot.com/6999043/diff/5001/src/cmd/8g/cgen.c#newcode404
src/cmd/8g/cgen.c:404: mfree(&n1);
please make this regfree then mfree, just to preserve nesting

[remyoudompheng, 2012-12-21 22:43:56]

On 2012/12/21 07:26:51, DMorsing wrote:
> Got any before and after assembly comparisons?

I see no difference for the following input:

package p

func F(a, b, c byte) byte {
      return a*(a*b+17)+c
}

--- prog list "F" ---
0000 (test.go:3) TEXT    F+0(SB),$0-8
0001 (test.go:3) MOVBLZX a+0(FP),DX
0002 (test.go:4) MOVBLZX b+1(FP),BX
0003 (test.go:4) MOVBLZX DX,BP
0004 (test.go:4) IMULL   BP,BX
0005 (test.go:4) ADDL    $17,BX
0006 (test.go:4) MOVL    BX,AX
0007 (test.go:4) MOVBLZX DX,BX
0008 (test.go:4) MOVBLZX AX,BP
0009 (test.go:4) IMULL   BP,BX
0010 (test.go:4) ADDB    c+2(FP),BX
0011 (test.go:4) MOVB    BX,.noname+4(FP)
0012 (test.go:4) RET     ,

There may be some perturbations or extra temporaries when there is a lot of byte
arithmetic but it's hardly perceptible.

[remyoudompheng, 2012-12-21 22:46:21]

*** Submitted as https://code.google.com/p/go/source/detail?r=6fdc1974457c ***

cmd/8g: introduce temporaries in byte multiplication.

Also restore the smallintconst case for binary ops.

Fixes issue 3835.

R=daniel.morsing, rsc
CC=golang-dev
https://codereview.appspot.com/6999043

https://codereview.appspot.com/6999043/diff/5001/src/cmd/8g/cgen.c
File src/cmd/8g/cgen.c (right):

https://codereview.appspot.com/6999043/diff/5001/src/cmd/8g/cgen.c#newcode404
src/cmd/8g/cgen.c:404: mfree(&n1);
On 2012/12/21 21:21:36, rsc wrote:
> please make this regfree then mfree, just to preserve nesting

Done.