[FFmpeg-devel] [WIP][PATCH] Opus Piramid Vector Quantization Search in x86 SIMD asm

[Ivan Kalvachev]

On 6/11/17, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> On Sun, Jun 11, 2017 at 11:34 AM, Ivan Kalvachev <ikalvachev at gmail.com>
> wrote:
>> On 6/10/17, James Darnley <james.darnley at gmail.com> wrote:
>>> On 2017-06-09 13:41, Ivan Kalvachev wrote:
>>>> On 6/9/17, Michael Niedermayer <michael at niedermayer.cc> wrote:
>>>>> seems this breaks build with mingw64, didnt investigate but it
>>>>> fails with these errors:
>>>>>
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0x2d):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0x3fd):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0x7a1):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0xb48):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0x2d):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0x3fd):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0x7a1):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> libavcodec/libavcodec.a(opus_pvq_search.o):src/libavcodec/x86/opus_pvq_search.asm:(.text+0xb48):
>>>>> relocation truncated to fit: R_X86_64_32 against `const_align_abs_edge'
>>>>> collect2: error: ld returned 1 exit status
>>>>> collect2: error: ld returned 1 exit status
>>>>> make: *** [ffmpeg_g.exe] Error 1
>>>>> make: *** Waiting for unfinished jobs....
>>>>> make: *** [ffprobe_g.exe] Error 1
>>>>
>>>>
>>>> const_*_edge is used on only one place is the code.
>>>> Would you check if this patch fixes the issue.
>>>>
>>>> I expected that the addresses would be pre-calculated
>>>> by n/yasm as one value and indexed
>>>> relative to the section start.
>>>> Instead it seems that each entry is represented with
>>>> its own address and offset from it.
>>>> Since the offset is negative it uses all 64 bits and
>>>> it makes difference if it is truncated to 32 bits.
>>>>
>>>> Same issue could happen with clang tools.
>>>
>>> The problem is with the relative addressing.  You need to load the real
>>> address first before you can offset with another register at runtime. So
>>> something like:
>>>
>>>> mov  reg1,  [read_only_const]
>> lea ?
>>>> mova mmreg, [reg1 + reg2]
>>
>> .
>> OK, Getting mingw for my distro is problem
>> and compiling one myself would take a bit more effort/time.
>> So I'm posting a patch that "should" work.
>> ======
>> --- a/libavcodec/x86/opus_pvq_search.asm
>> +++ b/libavcodec/x86/opus_pvq_search.asm
>> @@ -406,7 +406,7 @@ align 16
>>  ; uint32 N      - Number of vector elements. Must be 0 < N < 8192
>>  ;
>>  %macro PVQ_FAST_SEARCH 0
>> -cglobal pvq_search,4,5,8, mmsize, inX, outY, K, N
>> +cglobal pvq_search,4,6,8, mmsize, inX, outY, K, N
>>  %define tmpX rsp
>>
>>  ;        movsxdifnidn Nq,  Nd
>> @@ -419,7 +419,12 @@ cglobal pvq_search,4,5,8, mmsize, inX, outY, K, N
>>          add         Nq,   r4q           ; Nq = align(Nq, mmsize)
>>          sub         rsp,  Nq            ; allocate tmpX[Nq]
>>
>> +%ifdef PIC
>> +        lea         r5q,  [const_align_abs_edge]            ; rip+const
>> +        movups      m3,   [r5q+r4q-mmsize]                  ; this is
>> the bit mask for the padded read at the end of the input
>> +%else
>>          movups      m3,   [const_align_abs_edge-mmsize+r4q] ; this is
>> the bit mask for the padded read at the end of the input
>> +%endif
>>
>>          lea         r4q,  [Nq-mmsize]   ; Nq is rounded up (aligned
>> up) to mmsize, so r4q can't become negative here, unless N=0.
>>          movups      m2,   [inXq + r4q]
>> ======
>>
>> What I find surprising is that PIC is enabled only on Windows and does not
>> seem
>> to depend on CONFIG_PIC, so textrels are used all over assembly code.
>> Do I miss something?
>>
>
> Win32 code is always PIC, independent of what ffmpeg configure thinks
> it should be. :)
> Using the PIC define seems to be the appropriate thing, thats what the
> other asm code does.
>

Yes, but my query is more about
why CONFIG_PIC does not enable asm PIC too?
After all gcc -fpic is supposed to generate code without texrel, isn't it?