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

[Connor Abbott]

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:
>> It now emits vector MOVs instead of a series of individual MOVs, which
>> should be useful to any vector backends.  This pushes the problem of
>> src/dest aliasing of channels on a scalar chip to the backend, but if
>> there are any vector operations in your shader then you needed to be
>> handling this already.
>>
>> Fixes fs-swap-problem with my scalarizing patches.
>> ---
>>  src/glsl/nir/nir_lower_vec_to_movs.c | 74 +++++++++++++++++++++++++++++++-----
>>  1 file changed, 64 insertions(+), 10 deletions(-)
>>
>> diff --git a/src/glsl/nir/nir_lower_vec_to_movs.c b/src/glsl/nir/nir_lower_vec_to_movs.c
>> index 022889e..489901e 100644
>> --- a/src/glsl/nir/nir_lower_vec_to_movs.c
>> +++ b/src/glsl/nir/nir_lower_vec_to_movs.c
>> @@ -33,6 +33,49 @@
>>   */
>>
>>  static bool
>> +src_matches_dest_reg(nir_dest *dest, nir_src *src)
>> +{
>> +   if (dest->is_ssa || src->is_ssa)
>> +      return false;
>> +
>> +   return (dest->reg.reg == src->reg.reg &&
>> +           dest->reg.base_offset == src->reg.base_offset &&
>> +           !dest->reg.indirect &&
>> +           !src->reg.indirect);
>> +}
>> +
>> +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().

>> +{
>> +   unsigned src_idx = start_src_idx;
>> +   assert(src_idx < nir_op_infos[vec->op].num_inputs);
>> +
>> +   nir_alu_instr *mov = nir_alu_instr_create(mem_ctx, nir_op_imov);
>> +   nir_alu_src_copy(&mov->src[0], &vec->src[src_idx], mem_ctx);
>> +   nir_alu_dest_copy(&mov->dest, &vec->dest, mem_ctx);
>> +
>> +   mov->dest.write_mask = (1u << start_channel);
>> +   mov->src[0].swizzle[start_channel] = vec->src[src_idx].swizzle[0];
>> +   src_idx++;
>> +
>> +   for (unsigned i = start_channel + 1; i < 4; i++) {
>> +      if (!(vec->dest.write_mask & (1 << i)))
>> +         continue;
>> +
>> +      if (nir_srcs_equal(vec->src[src_idx].src, vec->src[start_src_idx].src)) {
>> +         mov->dest.write_mask |= (1 << i);
>> +         mov->src[0].swizzle[i] = vec->src[src_idx].swizzle[0];
>> +      }
>> +      src_idx++;
>> +   }
>> +
>> +   nir_instr_insert_before(&vec->instr, &mov->instr);
>> +
>> +   return mov->dest.write_mask;
>> +}
>> +
>> +static bool
>>  lower_vec_to_movs_block(nir_block *block, void *mem_ctx)
>>  {
>>     nir_foreach_instr_safe(block, instr) {
>> @@ -50,22 +93,33 @@ lower_vec_to_movs_block(nir_block *block, void *mem_ctx)
>>           continue; /* The loop */
>>        }
>>
>> +      /* Since we insert multiple MOVs, we have to be non-SSA. */
>> +      assert(!vec->dest.dest.is_ssa);
>> +
>> +      unsigned finished_write_mask = 0;
>> +
>> +      /* First, emit a MOV for all the src channels that are in the
>> +       * destination reg, in case other values we're populating in the dest
>> +       * might overwrite them.
>> +       */
>>        for (unsigned i = 0, src_idx = 0; i < 4; i++) {
>>           if (!(vec->dest.write_mask & (1 << i)))
>>              continue;
>>
>> -         assert(src_idx < nir_op_infos[vec->op].num_inputs);
>> -
>> -         nir_alu_instr *mov = nir_alu_instr_create(mem_ctx, nir_op_imov);
>> -         nir_alu_src_copy(&mov->src[0], &vec->src[src_idx], mem_ctx);
>> -
>> -         /* We only care about the one swizzle */
>> -         mov->src[0].swizzle[i] = vec->src[src_idx].swizzle[0];
>> +         if (src_matches_dest_reg(&vec->dest.dest, &vec->src[src_idx].src)) {
>> +            finished_write_mask |= insert_movs(vec, i, src_idx, mem_ctx);
>> +            break;
>> +         }
>> +         src_idx++;
>> +      }
>>
>> -         nir_alu_dest_copy(&mov->dest, &vec->dest, mem_ctx);
>> -         mov->dest.write_mask = (1u << i);
>> +      /* Now, emit MOVs for all the other src channels. */
>> +      for (unsigned i = 0, src_idx = 0; i < 4; i++) {
>> +         if (!(vec->dest.write_mask & (1 << i)))
>> +            continue;
>>
>> -         nir_instr_insert_before(&vec->instr, &mov->instr);
>> +         if (!(finished_write_mask & (1 << i)))
>> +            finished_write_mask |= insert_movs(vec, i, src_idx, mem_ctx);
>>
>>           src_idx++;
>>        }
>> --
>> 2.1.3
>>
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