Matt Turner <matts...@gmail.com> writes:
> On Mon, Feb 29, 2016 at 7:30 AM, Iago Toral <ito...@igalia.com> wrote:
>> On Fri, 2016-02-26 at 22:02 -0800, Francisco Jerez wrote:
>>> swizzle() works for vector immediates other than VF.
>>> ---
>>> .../drivers/dri/i965/brw_vec4_copy_propagation.cpp | 19
>>> +------------------
>>> 1 file changed, 1 insertion(+), 18 deletions(-)
>>>
>>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> index 6bd9928..5c25164 100644
>>> --- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> +++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>>> @@ -76,22 +76,6 @@ is_channel_updated(vec4_instruction *inst, src_reg
>>> *values[4], int ch)
>>> inst->dst.writemask & (1 << BRW_GET_SWZ(src->swizzle, ch)));
>>> }
>>>
>>> -static unsigned
>>> -swizzle_vf_imm(unsigned vf4, unsigned swizzle)
>>> -{
>>> - union {
>>> - unsigned vf4;
>>> - uint8_t vf[4];
>>> - } v = { vf4 }, ret;
>>> -
>>> - ret.vf[0] = v.vf[BRW_GET_SWZ(swizzle, 0)];
>>> - ret.vf[1] = v.vf[BRW_GET_SWZ(swizzle, 1)];
>>> - ret.vf[2] = v.vf[BRW_GET_SWZ(swizzle, 2)];
>>> - ret.vf[3] = v.vf[BRW_GET_SWZ(swizzle, 3)];
>>> -
>>> - return ret.vf4;
>>> -}
>>> -
>>> static bool
>>> is_logic_op(enum opcode opcode)
>>> {
>>> @@ -144,8 +128,7 @@ try_constant_propagate(const struct brw_device_info
>>> *devinfo,
>>> }
>>> }
>>>
>>> - if (value.type == BRW_REGISTER_TYPE_VF)
>>> - value.ud = swizzle_vf_imm(value.ud, inst->src[arg].swizzle);
>>> + value = swizzle(value, inst->src[arg].swizzle);
>>
>> so I guess V/UV was broken before this?
>
> My question is in the same vein -- what does swizzling V/UV even mean?
> Swizzles operate on 4-component things, but V/UV have 8 components.
>
swizzle() operates on 8-component things 99% of the time. Its semantics
are determined by the equivalence of:OP ..., swizzle(x, swz) to: MOV tmp, x OP ..., tmp.swz where the MOV has the same execution type and width as the arbitrary instruction OP. With this in mind there are no restrictions on what x can be, as long as it can be read from, you just do what the hardware does. > Concretely, for an immediate of 0x1234567UV, what does applying a > swizzle of .yxzw do? Does it swap two dwords (each containing two > values) and produce 0x34125678UV? Or does it operate on both halves > individually and produce 0x21346578UV? > At the hardware level a swizzle specifies a permutation of 4 which is cyclically extended to whatever the vector width is. So assuming your immediate is 0x01234567UV the correct answer is 0x01324576UV. > Moreover, using one of these immediate types requires a W destination, I don't think that's right. > which isn't possible in align16 instructions -- so swizzling V/UV > seems pointless. We use V *and* a W destination in Align16 mode in gen6_gs_visitor.cpp:617. Admittedly the instruction looks rather weird and I considered replacing it with something else, but there's no harm in swizzle() handling its whole domain consistently, and I didn't feel comfortable about leaving this one case unimplemented and letting the program crash whenever a V/UV immediate comes up in some optimization pass that happens to use swizzle(), which may happen as long as something in the vec4 back-end continues using V/UV. > > Remove the V/UV code from 2/5 and 3/5?
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