[x264-devel] unaligned accesses in IA64

[Mauricio Alvarez]

Hi,

On Thu, Feb 28, 2008 at 2:16 PM, Loren Merritt <lorenm at u.washington.edu> wrote:
> On Tue, 26 Feb 2008, Mauricio Alvarez wrote:
>  > x264(8689): unaligned access to 0x607fffffff32ee5c, ip=0x40000000000afb71
>  > x264(8689): unaligned access to 0x607fffffff32ee64, ip=0x40000000000aff31
>
>  The obvious step is to disassemble it and see what pieces of code
>  correspond to addresses 0x40000000000afb71 and 0x40000000000aff31.


I repetead the test with the following configuration: gcc with -01 -g
(--enable-debug). Using different input videos and different number of
frames to encode I found the following unaligned accesses:
x264(11582): unaligned access to 0x607ffffffece29ac, ip=0x400000000005d901
x264(11582): unaligned access to 0x607ffffffece29b4, ip=0x400000000005dd50
x264(11582): unaligned access to 0x607ffffffece29ac, ip=0x400000000005d2b1
x264(12585): unaligned access to 0x607ffffffeac69cc, ip=0x400000000005d2f0
x264(12585): unaligned access to 0x607ffffffeac69ac, ip=0x400000000005cb00
x264(12585): unaligned access to 0x607ffffffeac69b4, ip=0x400000000005cb20
x264(12585): unaligned access to 0x607ffffffeac69b4, ip=0x400000000005d2d1

the most common one is: x264(11582): unaligned access to
0x607ffffffece29b4, ip=0x400000000005dd50

All these accesses correspond to stores to the mvc array in
x264_mb_analyse_inter_XXX functions in analyse.c . The problem is that
the base address that these functions are receiving is not 64-bit
aligned.
Just an example from the function x264_mb_analyse_inter_p8x8():

// initialization of mvc
//encoder/analyse.c:1100
    int (*mvc)[2] = a->l0.mvc[i_ref];

// access to mvc
//encoder/analyse.c:1107
*(uint64_t*)mvc[0] = *(uint64_t*)a->l0.me16x16.mv;
400000000005d8f6:       f0 00 84 08 42 00                   adds r15=512,r33;;
400000000005d8fc:       00 00 04 00                         nop.i 0x0
400000000005d900:       0b 78 00 1e 18 10       [MMI]       ld8 r15=[r15];;

// access to mvc
//encoder/analyse.c:1127
*(uint64_t*)mvc[i_mvc] = *(uint64_t*)m->mv;
400000000005dd40:       0b 70 00 40 01 21       [MMI]       adds r14=128,r32;;
400000000005dd46:       e0 00 38 30 20 00                   ld8 r14=[r14]
400000000005dd4c:       00 00 04 00                         nop.i 0x0;;
400000000005dd50:       02 40 38 56 98 15       [MII]       st8 [r43]=r14,8

I'm not familiar with the X264 code, so I ask this: it is possible to
force (by using a compiler directive) a specific alignment  to these
pointers? Or are there generated dynamically by motion estimation?.

Regards,

Mauricio A.