On Mon, Mar 19, 2012 at 12:25 PM, Ronald S. Bultje <[email protected]> wrote:
> Hi,
>
> On Mon, Mar 19, 2012 at 12:03 PM, Jason Garrett-Glaser <[email protected]> wrote:
>> On Mon, Mar 19, 2012 at 10:14 AM, Ronald S. Bultje <[email protected]>
>> wrote:
>>> On Mon, Mar 19, 2012 at 9:48 AM, Jason Garrett-Glaser <[email protected]>
>>> wrote:
>>>> On Sat, Mar 17, 2012 at 9:34 AM, Ronald S. Bultje <[email protected]>
>>>> wrote:
>>>>> ---
>>>>> libavcodec/x86/cabac.h | 17 ++++++++++-------
>>>>> 1 files changed, 10 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/libavcodec/x86/cabac.h b/libavcodec/x86/cabac.h
>>>>> index 3c3652d..c4832c3 100644
>>>>> --- a/libavcodec/x86/cabac.h
>>>>> +++ b/libavcodec/x86/cabac.h
>>>>> @@ -105,8 +105,8 @@ static av_always_inline int
>>>>> get_cabac_bypass_sign_x86(CABACContext *c, int val)
>>>>> {
>>>>> x86_reg tmp;
>>>>> __asm__ volatile(
>>>>> - "movl %4, %k1 \n\t"
>>>>> - "movl %2, %%eax \n\t"
>>>>> + "movl %c5(%2), %k1 \n\t"
>>>>> + "movl %c3(%2), %%eax \n\t"
>>>>> "shl $17, %k1 \n\t"
>>>>> "add %%eax, %%eax \n\t"
>>>>> "sub %k1, %%eax \n\t"
>>>>> @@ -117,7 +117,7 @@ static av_always_inline int
>>>>> get_cabac_bypass_sign_x86(CABACContext *c, int val)
>>>>> "sub %%edx, %%ecx \n\t"
>>>>> "test %%ax, %%ax \n\t"
>>>>> " jnz 1f \n\t"
>>>>> - "mov %3, %1 \n\t"
>>>>> + "mov %c4(%2), %1 \n\t"
>>>>> "subl $0xFFFF, %%eax \n\t"
>>>>> "movzwl (%1), %%edx \n\t"
>>>>> "bswap %%edx \n\t"
>>>>> @@ -126,11 +126,14 @@ static av_always_inline int
>>>>> get_cabac_bypass_sign_x86(CABACContext *c, int val)
>>>>> "addl %%edx, %%eax \n\t"
>>>>> "mov %1, %3 \n\t"
>>>>> "1: \n\t"
>>>>> - "movl %%eax, %2 \n\t"
>>>>> + "movl %%eax, %c4(%2) \n\t"
>>>>>
>>>>> - :"+c"(val), "=&r"(tmp), "+m"(c->low), "+m"(c->bytestream)
>>>>> - :"m"(c->range)
>>>>> - : "%eax", "%edx"
>>>>> + : "+c"(val), "=&r"(tmp)
>>>>> + : "r"(c),
>>>>> + "i"(offsetof(CABACContext, low)),
>>>>> + "i"(offsetof(CABACContext, bytestream)),
>>>>> + "i"(offsetof(CABACContext, range))
>>>>> + : "%eax", "%edx", "memory"
>>>>
>>>> IMO clobbering memory looks very very hacky, and I don't like it. If
>>>> you need to clobber something, it'd be much better if we could clobber
>>>> exactly what needs clobbering, and nothing more.
>>>
>>> Well, I don't think inline assembly supports explicitely clobbering
>>> variables without marking them as "+m" or "+r", which messes up the
>>> register allocator for at least gcc-4.2.1 (it uses a different
>>> register for each "m"(c->...), thus running out of registers; yes,
>>> there's many things wrong there).
>>
>> You can clobber a memory location without referencing it in the asm,
>> and thus without allocating a register for it.
>
> That sounds useful, how do I do that?
Just add +m arguments and don't use them, that's all.
Here's an example from an unfinished patch of mine:
+static ALWAYS_INLINE void x264_cabac_encode_decision( x264_cabac_t
*cb, int i_ctx, int b )
+{
+ asm(
+ "call %P8\n"
+ :"+S"(i_ctx),"+d"(b), "+D"(cb->i_range), "+m"(cb->i_low),
"+m"(cb->i_queue), "+m"(cb->i_bytes_outstanding), "+m"(cb->p)
+ :"a"(cb),"X"(x264_cabac_encode_decision_asm)
+ :"%ecx"
+ );
+}
Jason
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