On Monday 25 April 2005 18:53, Andi Kleen wrote:
> On Mon, Apr 25, 2005 at 10:19:30AM +0300, Denis Vlasenko wrote:
> > I noticed that swab64 explicitly swaps 32-bit halves, but this is
> > not really needed because CPU is 32-bit anyway and we can
> > just tell GCC to treat registers as being swapped.
>
> No, we went through this exactly when the code was originally done.
> gcc puts long long only into aligned register pairs, and with
I don't see this. However, gcc is indeed does some unneeded moves,
both with and without xchgl. I filed a bug report:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21202
> register swap you need at least 4 registers which blows near
> all possible registers away and completely breaks register
> allocation in the function. Dont apply this!
Andi, are you saying that code gets worse with this patch?
This is not true at least for gcc 3.4.3 and 4.0.0.
I just re-checked this.
This is with original code:
# objdump -r -d crypto/wp512.o
00000000 <wp512_process_buffer>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 57 push %edi
4: 56 push %esi
5: 53 push %ebx
6: 81 ec 00 02 00 00 sub $0x200,%esp
c: 31 ff xor %edi,%edi
e: 8b 4d 08 mov 0x8(%ebp),%ecx
11: 8b 54 f9 24 mov 0x24(%ecx,%edi,8),%edx
15: 8b 44 f9 20 mov 0x20(%ecx,%edi,8),%eax
19: 8d 77 01 lea 0x1(%edi),%esi
1c: 89 b5 f4 fd ff ff mov %esi,0xfffffdf4(%ebp)
22: 89 c1 mov %eax,%ecx
24: 89 d6 mov %edx,%esi
26: 0f c9 bswap %ecx
28: 0f ce bswap %esi
2a: 87 ce xchg %ecx,%esi <=======
2c: 89 8c fd 74 ff ff ff mov %ecx,0xffffff74(%ebp,%edi,8)
33: 89 b4 fd 78 ff ff ff mov %esi,0xffffff78(%ebp,%edi,8)
Patched:
# objdump -r -d crypto_noswap/wp512.o
00000000 <wp512_process_buffer>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 57 push %edi
4: 56 push %esi
5: 53 push %ebx
6: 81 ec 00 02 00 00 sub $0x200,%esp
c: 31 ff xor %edi,%edi
e: 8b 4d 08 mov 0x8(%ebp),%ecx
11: 8b 44 f9 20 mov 0x20(%ecx,%edi,8),%eax
15: 8b 54 f9 24 mov 0x24(%ecx,%edi,8),%edx
19: 8d 77 01 lea 0x1(%edi),%esi
1c: 89 b5 f4 fd ff ff mov %esi,0xfffffdf4(%ebp)
22: 89 c3 mov %eax,%ebx
24: 89 d6 mov %edx,%esi
26: 0f cb bswap %ebx
28: 0f ce bswap %esi
<========= NO xchg
2a: 89 b4 fd 74 ff ff ff mov %esi,0xffffff74(%ebp,%edi,8)
31: 89 9c fd 78 ff ff ff mov %ebx,0xffffff78(%ebp,%edi,8)
It is not a win only for wp512, other crypto modules are a tiny bit smaller too:
# echo crypto*/*.o | xargs -n1 | grep -Fv .mod. | sort -t / -k2,99 | xargs size
text data bss dec hex filename
17743 108 0 17851 45bb crypto/khazad.o
17735 108 0 17843 45b3 crypto_noswap/khazad.o
666 108 0 774 306 crypto/sha1.o
664 108 0 772 304 crypto_noswap/sha1.o
5160 364 0 5524 1594 crypto/sha512.o
5156 364 0 5520 1590 crypto_noswap/sha512.o
10239 364 0 10603 296b crypto/tgr192.o
10233 364 0 10597 2965 crypto_noswap/tgr192.o
22774 364 0 23138 5a62 crypto/wp512.o
22770 364 0 23134 5a5e crypto_noswap/wp512.o
--
vda
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