[Mesa-dev] [PATCH 2/3] nir: Add a pass to lower outputs to temporary variables

[Jason Ekstrand]

On Tue, Sep 8, 2015 at 5:30 PM, Ian Romanick <idr at freedesktop.org> wrote:
> On 09/08/2015 04:51 PM, Jason Ekstrand wrote:
>> This pass can be used as a helper for NIR producers so they don't have to
>> worry about creating the temporaries themselves.
>> ---
>>  src/glsl/Makefile.sources                       |   1 +
>>  src/glsl/nir/nir.h                              |   2 +
>>  src/glsl/nir/nir_lower_outputs_to_temporaries.c | 131 ++++++++++++++++++++++++
>>  3 files changed, 134 insertions(+)
>>  create mode 100644 src/glsl/nir/nir_lower_outputs_to_temporaries.c
>>
>> diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
>> index c422303..6c2854f 100644
>> --- a/src/glsl/Makefile.sources
>> +++ b/src/glsl/Makefile.sources
>> @@ -40,6 +40,7 @@ NIR_FILES = \
>>       nir/nir_lower_locals_to_regs.c \
>>       nir/nir_lower_idiv.c \
>>       nir/nir_lower_io.c \
>> +     nir/nir_lower_outputs_to_temporaries.c \
>>       nir/nir_lower_phis_to_scalar.c \
>>       nir/nir_lower_samplers.cpp \
>>       nir/nir_lower_system_values.c \
>> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
>> index c4db005..3b9d504 100644
>> --- a/src/glsl/nir/nir.h
>> +++ b/src/glsl/nir/nir.h
>> @@ -1786,6 +1786,8 @@ void nir_lower_global_vars_to_local(nir_shader *shader);
>>
>>  void nir_lower_locals_to_regs(nir_shader *shader);
>>
>> +void nir_lower_outputs_to_temporaries(nir_shader *shader);
>> +
>>  void nir_assign_var_locations(struct exec_list *var_list,
>>                                unsigned *size,
>>                                int (*type_size)(const struct glsl_type *));
>> diff --git a/src/glsl/nir/nir_lower_outputs_to_temporaries.c b/src/glsl/nir/nir_lower_outputs_to_temporaries.c
>> new file mode 100644
>> index 0000000..dd84ed4
>> --- /dev/null
>> +++ b/src/glsl/nir/nir_lower_outputs_to_temporaries.c
>> @@ -0,0 +1,131 @@
>> +/*
>> + * Copyright © 2015 Intel Corporation
>> + *
>> + * Permission is hereby granted, free of charge, to any person obtaining a
>> + * copy of this software and associated documentation files (the "Software"),
>> + * to deal in the Software without restriction, including without limitation
>> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
>> + * and/or sell copies of the Software, and to permit persons to whom the
>> + * Software is furnished to do so, subject to the following conditions:
>> + *
>> + * The above copyright notice and this permission notice (including the next
>> + * paragraph) shall be included in all copies or substantial portions of the
>> + * Software.
>> + *
>> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
>> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
>> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
>> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
>> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
>> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
>> + * IN THE SOFTWARE.
>> + *
>> + * Authors:
>> + *    Jason Ekstrand (jason at jlekstrand.net)
>
> GIT will keep track of this for us. :) We stopped putting by-lines in
> the code a long, long time ago.  I sent out some patches a couple weeks
> ago to remove all the remaining by-lines from src/drivers/dri/i965.

Yeah, I saw that.  I just copied-and-pasted this header from something
pre-cleanups.  I'll can it.

> Assuming that there are no shader-db regressions, this series is
>
> Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

Thanks!

>> + *
>> + */
>> +
>> +/*
>> + * Implements a pass that lowers output variables to a temporary plus an
>> + * output variable with a single copy at each exit point of the shader.
>> + * This way the output variable is only ever written.
>> + *
>> + * Because valid NIR requires that output variables are never read, this
>> + * pass is more of a helper for NIR producers and must be run before the
>> + * shader is ever validated.
>> + */
>> +
>> +#include "nir.h"
>> +
>> +struct lower_outputs_state {
>> +   nir_shader *shader;
>> +   struct exec_list old_outputs;
>> +};
>> +
>> +static void
>> +emit_output_copies(nir_cursor cursor, struct lower_outputs_state *state)
>> +{
>> +   assert(exec_list_length(&state->shader->outputs) ==
>> +          exec_list_length(&state->old_outputs));
>> +
>> +   foreach_two_lists(out_node, &state->shader->outputs,
>> +                     temp_node, &state->old_outputs) {
>> +      nir_variable *output = exec_node_data(nir_variable, out_node, node);
>> +      nir_variable *temp = exec_node_data(nir_variable, temp_node, node);
>> +
>> +      nir_intrinsic_instr *copy =
>> +         nir_intrinsic_instr_create(state->shader, nir_intrinsic_copy_var);
>> +      copy->variables[0] = nir_deref_var_create(copy, output);
>> +      copy->variables[1] = nir_deref_var_create(copy, temp);
>> +
>> +      nir_instr_insert(cursor, &copy->instr);
>> +   }
>> +}
>> +
>> +static bool
>> +emit_output_copies_block(nir_block *block, void *state)
>> +{
>> +   nir_foreach_instr(block, instr) {
>> +      if (instr->type != nir_instr_type_intrinsic)
>> +         continue;
>> +
>> +      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
>> +      if (intrin->intrinsic == nir_intrinsic_emit_vertex)
>> +         emit_output_copies(nir_before_instr(&intrin->instr), state);
>> +   }
>> +
>> +   return true;
>> +}
>> +
>> +void
>> +nir_lower_outputs_to_temporaries(nir_shader *shader)
>> +{
>> +   struct lower_outputs_state state;
>> +
>> +   state.shader = shader;
>> +   exec_list_move_nodes_to(&shader->outputs, &state.old_outputs);
>> +
>> +   /* Walk over all of the outputs turn each output into a temporary and
>> +    * make a new variable for the actual output.
>> +    */
>> +   foreach_list_typed(nir_variable, var, node, &state.old_outputs) {
>> +      nir_variable *output = ralloc(shader, nir_variable);
>> +      memcpy(output, var, sizeof *output);
>> +
>> +      /* The orignal is now the temporary */
>> +      nir_variable *temp = var;
>> +
>> +      /* Give the output a new name with @out-temp appended */
>> +      temp->name = ralloc_asprintf(var, "%s at out-temp", output->name);
>> +      temp->data.mode = nir_var_global;
>> +      temp->constant_initializer = NULL;
>> +
>> +      exec_list_push_tail(&shader->outputs, &output->node);
>> +   }
>> +
>> +   nir_foreach_overload(shader, overload) {
>> +      if (overload->impl == NULL)
>> +         continue;
>> +
>> +      if (shader->stage == MESA_SHADER_GEOMETRY) {
>> +         /* For geometry shaders, we have to emit the output copies right
>> +          * before each EmitVertex call.
>> +          */
>> +         nir_foreach_block(overload->impl, emit_output_copies_block, &state);
>> +      } else if (strcmp(overload->function->name, "main") == 0) {
>> +         /* For all other shader types, we need to do the copies right before
>> +          * the jumps to the end block.
>> +          */
>> +         struct set_entry *block_entry;
>> +         set_foreach(overload->impl->end_block->predecessors, block_entry) {
>> +            struct nir_block *block = (void *)block_entry->key;
>> +            emit_output_copies(nir_after_block_before_jump(block), &state);
>> +         }
>> +      }
>> +
>> +      nir_metadata_preserve(overload->impl, nir_metadata_block_index |
>> +                                            nir_metadata_dominance);
>> +   }
>> +
>> +   exec_list_append(&shader->globals, &state.old_outputs);
>> +}
>