On 01/21/2015 03:05 PM, Matt Turner wrote:
> On Wed, Jan 21, 2015 at 2:52 PM, Kenneth Graunke <kenn...@whitecape.org>
> wrote:
>> On Wednesday, January 21, 2015 01:02:46 PM Matt Turner wrote:
>>> On Tue, Jan 20, 2015 at 12:11 AM, Kenneth Graunke <kenn...@whitecape.org>
>>> wrote:
>>>> On Monday, January 19, 2015 03:31:05 PM Matt Turner wrote:
>>>>> ---
>>>>> src/mesa/drivers/dri/i965/brw_eu.c | 22 ++++++++++++++++++++++
>>>>> src/mesa/drivers/dri/i965/brw_eu.h | 1 +
>>>>> 2 files changed, 23 insertions(+)
>>>>>
>>>>> diff --git a/src/mesa/drivers/dri/i965/brw_eu.c
>>>>> b/src/mesa/drivers/dri/i965/brw_eu.c
>>>>> index 9905972..9977eed 100644
>>>>> --- a/src/mesa/drivers/dri/i965/brw_eu.c
>>>>> +++ b/src/mesa/drivers/dri/i965/brw_eu.c
>>>>> @@ -88,6 +88,28 @@ brw_swap_cmod(uint32_t cmod)
>>>>> }
>>>>> }
>>>>>
>>>>> +/* Returns the corresponding inverted conditional mod. */
>>>>> +enum brw_conditional_mod
>>>>> +brw_invert_cmod(enum brw_conditional_mod cmod)
>>>>> +{
>>>>> + switch (cmod) {
>>>>> + case BRW_CONDITIONAL_Z:
>>>>> + return BRW_CONDITIONAL_NZ;
>>>>> + case BRW_CONDITIONAL_NZ:
>>>>> + return BRW_CONDITIONAL_Z;
>>>>> + case BRW_CONDITIONAL_G:
>>>>> + return BRW_CONDITIONAL_LE;
>>>>> + case BRW_CONDITIONAL_GE:
>>>>> + return BRW_CONDITIONAL_L;
>>>>> + case BRW_CONDITIONAL_L:
>>>>> + return BRW_CONDITIONAL_GE;
>>>>> + case BRW_CONDITIONAL_LE:
>>>>> + return BRW_CONDITIONAL_G;
>>>>> + default:
>>>>> + return BRW_CONDITIONAL_NONE;
>>>>> + }
>>>>> +}
>>>>
>>>> Heh, I thought this looked familiar...apparently I wrote one too :)
>>>> http://lists.freedesktop.org/archives/mesa-dev/2014-August/066127.html
>>>>
>>>> I wasn't sure whether "invert" meant "flip direction" or "negate condition"
>>>> until I read the code. How about calling it brw_negate_cmod instead?
>>>>
>>>> /* Returns a conditional modifier that negates the condition. */
>>>> enum brw_conditional_mod
>>>> brw_negate_cmod(uint32_t cmod)
>>>> {
>>>> ...
>>>> }
>>>>
>>>> Either way is fine.
>>>> Reviewed-by: Kenneth Graunke <kenn...@whitecape.org>
>>>
>>> Okay, I changed the name, and in the process of thinking about that
>>> and a comment Jason made I realized that part of this function was
>>> wrong. When you negate, you don't want to swap Z <-> NZ. I've changed
>>> the function accordingly:
>>>
>>> + switch (cmod) {
>>> + case BRW_CONDITIONAL_Z:
>>> + case BRW_CONDITIONAL_NZ:
>>> + return cmod;
>>> [snip]
>>
>> What? This function takes a comparison that produces "A" and gives you
>> a new one that produces "!A".
>
> No. It gives the conditional mod you get by negating both operands of
> the comparison.
Which is the same as if you commute the arguments, right? Maybe
brw_cmod_for_commuted_args or brw_cmod_for_negated_args is a better
name. Based on this discussion, I think the function pre-comment is
also a little misleading. It sounds like it returns the !A cmod.
>> You absolutely have to change == to != (and
>> vice versa), or the function is just plain broken. You had it right the
>> first time.
>>
>> brw_swap_cmod doesn't do that, because it takes `X CMP Y` => A and
>> returns a new comparison such that `Y CMP' X` >= A. In other words, if
>> X < Y, then Y > X. But if X == Y, then Y == X.
>
> If you review the rest of the series (please do!), you'll see this
> function used in patch 14/16. The commit message gives an example of
> where we want to use this function, transforming:
>
> add(8) temp a b
> cmp.l.f0(8) null -temp 0.0
>
> into
>
> add.ge.f0(8) temp a b
>
> Imagine that was instead of cmp.l.f0, cmp.z.f0:
>
> add(8) temp a b
> cmp.z.f0(8) null -temp 0.0
>
> This is doing f0 = (-(a + b) == 0.0). If I swap Z <-> NZ, I'd get
>
> add.nz.f0(8) temp a b
>
> which would be f0 = ((a + b) != 0.0). In fact, we want the cmp's
> original .z on the add:
>
> add.z.f0(8) temp a b
>
> Perhaps there's a better name we can give the function?
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