"Ronald S. Bultje" <[email protected]> writes: > Hi, > > 2012/3/19 Måns Rullgård <[email protected]>: >> "Ronald S. Bultje" <[email protected]> writes: >>> 2012/3/19 Måns Rullgård <[email protected]>: >>>> "Ronald S. Bultje" <[email protected]> writes: >>>>> 2012/3/19 Måns Rullgård <[email protected]>: >>>>>> "Ronald S. Bultje" <[email protected]> writes: >>>>>>> On Sat, Mar 17, 2012 at 11:57 AM, Ronald S. Bultje <[email protected]> >>>>>>> wrote: >>>>>>>> 2012/3/17 Måns Rullgård <[email protected]>: >>>>>>>>> "Ronald S. Bultje" <[email protected]> writes: >>>>>>>>> >>>>>>>>>> --- >>>>>>>>>> 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" >>>>>>>>> >>>>>>>>> %c5? Last I checked, the code to get a plain number was 'a'. >>>>>>>> >>>>>>>> Fixed. >>>>>>>> >>>>>>>>>> - :"+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" >>>>>>>>> >>>>>>>>> We changed this to use "m" operands to avoid the memory clobber. I >>>>>>>>> know >>>>>>>>> why you're doing this, but I think it's the wrong approach. >>>>>>>> >>>>>>>> It generates better code (less instructions for e.g. >>>>>>>> decode_cabac_mb_mvd()) with gcc-4.2.1 (which is shipped with XCode). >>>>>>>> Does it generate worse code anywhere? (It's true that later on it adds >>>>>>>> instructions for the overread protection again, but this commit in >>>>>>>> isolation makes things better, not worse.) >>>>>>> >>>>>>> Ping, are there any practical concerns left? >>>>>> >>>>>> We're still no closer to understanding what really is going on here. >>>>> >>>>> You'll have to be more practical than "I don't get it, so let's do >>>>> nothing". Do something to understand it. This patchset improves things >>>>> on my end (better code, compiler doesn't bomb out on adding extra >>>>> argument such as bytestream_end), which is more than sufficient. >>>> >>>> Your compiler seems to be the only one where it gives better code. >>>> There is no guarantee that your compiler will keep doing this next time >>>> you upgrade it. Since I can't reproduce the problem, I'm not in a very >>>> good position to figure out why it happens. >>> >>> My compiler has been like that for years. >>> >>>> You can, and you're the one >>>> pushing for these patches, so the work falls to you. Tough luck. >>> >>> You're not very clear on what you want. You want the holy grail? You >>> want a time machine? You want a better pension? What falls on me? I've >>> written code that is (if I understand you correctly) the same for you, >>> and better for me. That's fantastic! So does that mean we agree I can >>> commit it? If not, what exactly is your problem with this code? >> >> You've made changes that have very unexpected results. This is never a >> good thing unless the reasons are understood. > > Yes: the compiler screwed up, and I fixed it.
No, you did not fix it. You randomly hacked around until it by chance did what you wanted. > Now, this isn't going anywhere. What are you looking for? I need a > concrete thing that you intend me to do, I want to understand what is causing the compiler to screw up in the first place. If we figure that out, we might find a clean solution. Usually the first step is to reduce the problem to a smaller test case. The function where this is happening isn't very large, so this should be fairly easy. > else I'll simply have to commit as-is. I don't like such threats. -- Måns Rullgård [email protected] _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
