code review 7100059: cmd/5l: move offset2 into Adr.u0 union to save 4/8 byte...

cmd/5l: move offset2 into Adr.u0 union to save 4/8 bytes for Adr/Prog resp.
sizeof(Adr) from 24 bytes down to 20 bytes.
sizeof(Prog) from 84 bytes down to 76 bytes.

5l linking cmd/godoc statistics:
Before:
Maximum resident set size (kbytes): 106668
After:
Maximum resident set size (kbytes):  99412

[dave_cheney.net, 2013-01-20 11:08:56]

LGTM. Wonderful saving

Tested on linux/arm on nexus7

(gdb) p sizeof(Adr)
$1 = 20
(gdb) p sizeof(Prog)
$2 = 72

[minux1, 2013-01-20 16:56:57]

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

I'd like you to review this change to
https://code.google.com/p/go/

[minux1, 2013-01-21 18:50:52]

*** Submitted as https://code.google.com/p/go/source/detail?r=5f4d7142d74e ***

cmd/5l: move offset2 into Adr.u0 union to save 4/8 bytes for Adr/Prog resp.
sizeof(Adr) from 24 bytes down to 20 bytes.
sizeof(Prog) from 84 bytes down to 76 bytes.

5l linking cmd/godoc statistics:
Before:
Maximum resident set size (kbytes): 106668
After:
Maximum resident set size (kbytes):  99412

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/7100059

[rsc, 2013-01-22 18:41:30]

Please name the struct fields u0offset and u0offset2.
Right now you are relying on the fact that in

#define offset u0.u0off.offset

the preprocessor does not reexpand rules it is already expanding. But small
changes could violate this. Better to use a unique name like before.

Russ

[minux1, 2013-01-23 08:35:20]

On Wed, Jan 23, 2013 at 2:41 AM, Russ Cox <rsc@golang.org> wrote:

> Please name the struct fields u0offset and u0offset2.
> Right now you are relying on the fact that in
>
> #define offset u0.u0off.offset
>
> the preprocessor does not reexpand rules it is already expanding. But
> small changes could violate this. Better to use a unique name like before.
>
Sure, the next time I change the header I will apply this change.