[Mesa-dev] [PATCH] nir: Make vec-to-movs handle src/dest aliasing.

[Eric Anholt]

Connor Abbott <cwabbott0 at gmail.com> writes:

> On Fri, Jan 23, 2015 at 5:34 PM, Eric Anholt <eric at anholt.net> wrote:
>> Connor Abbott <cwabbott0 at gmail.com> writes:
>>
>>> Argh, nevermind, I was reading it wrong...
>>>
>>> On Thu, Jan 22, 2015 at 8:18 PM, Connor Abbott <cwabbott0 at gmail.com> wrote:
>>>> What happens if you have something like foo = vec3(foo.z, bar.x,
>>>> foo.x)? I don't think emitting vector mov's for only the contiguous
>>>> components is enough.
>>>>
>>>> On Thu, Jan 22, 2015 at 4:51 PM, Eric Anholt <eric at anholt.net> wrote:
>>>>> +static unsigned
>>>>> +insert_movs(nir_alu_instr *vec, unsigned start_channel,
>>>>> +            unsigned start_src_idx, void *mem_ctx)
>>>
>>> We need a comment explaining what this function does and what it
>>> returns. Also, it only creates a single move so it should be called
>>> insert_mov().
>>
>> How about:
>>
>> /**
>>  * For a given writemask channel in the vec instruction, insert a MOV of all
>>  * the src values that come from the same reg to the destination of the vec
>>  * instruction.
>>  */
>
> First, I think we need to be a little more clear on what it does, e.g.
> "for a given starting channel/source, scans the rest of the sources of
> the vec instruction to find all sources that come from the same reg
> and emits a writemasked MOV from the reg to the destination of the vec
> instruction." Also, you need to explain what the return value is (a
> mask of all the channels/sources we inserted a MOV for).

Maybe:

/**
 * For a given starting writemask channel and corresponding source index in
 * the vec instruction, insert a MOV to the vec instruction's dest of all the
 * writemask channels that get read from the same src reg.
 *
 * Returns the writemask of our MOV, so the parent loop calling this knows
 * which ones have been processed.
 */
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