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.
> 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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