nir: Add a pass for lowering IO back to vector when possible

This pass tries to turn scalar and array-of-scalar IO variables into
vector IO variables whenever possible.

Reviewed-by: Connor Abbott <[email protected]>
Cc: "19.0" <[email protected]>

1 files changed, 387 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_lower_io_to_vector.c b/src/compiler/nir/nir_lower_io_to_vector.c
new file mode 100644
index 00000000000..d979962373d
--- /dev/null
+++ b/src/compiler/nir/nir_lower_io_to_vector.c
@@ -0,0 +1,387 @@
+/*
+ * Copyright © 2019 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.
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+#include "nir_deref.h"
+
+/** @file nir_lower_io_to_vector.c
+ *
+ * Merges compatible input/output variables residing in different components
+ * of the same location. It's expected that further passes such as
+ * nir_lower_io_to_temporaries will combine loads and stores of the merged
+ * variables, producing vector nir_load_input/nir_store_output instructions
+ * when all is said and done.
+ */
+
+static const struct glsl_type *
+resize_array_vec_type(const struct glsl_type *type, unsigned num_components)
+{
+   if (glsl_type_is_array(type)) {
+      const struct glsl_type *arr_elem =
+         resize_array_vec_type(glsl_get_array_element(type), num_components);
+      return glsl_array_type(arr_elem, glsl_get_length(type), 0);
+   } else {
+      assert(glsl_type_is_vector_or_scalar(type));
+      return glsl_vector_type(glsl_get_base_type(type), num_components);
+   }
+}
+
+static bool
+variable_can_rewrite(const nir_variable *var)
+{
+   /* Only touch user defined varyings as these are the only ones we split */
+   if (var->data.location < VARYING_SLOT_VAR0)
+      return false;
+
+   /* Skip complex types we don't split in the first place */
+   if (!glsl_type_is_vector_or_scalar(glsl_without_array(var->type)))
+      return false;
+
+   /* TODO: add 64/16bit support ? */
+   if (glsl_get_bit_size(glsl_without_array(var->type)) != 32)
+      return false;
+
+   return true;
+}
+
+static bool
+variables_can_merge(nir_shader *shader,
+                    const nir_variable *a, const nir_variable *b)
+{
+   const struct glsl_type *a_type_tail = a->type;
+   const struct glsl_type *b_type_tail = b->type;
+
+   /* They must have the same array structure */
+   while (glsl_type_is_array(a_type_tail)) {
+      if (!glsl_type_is_array(b_type_tail))
+         return false;
+
+      if (glsl_get_length(a_type_tail) != glsl_get_length(b_type_tail))
+         return false;
+
+      a_type_tail = glsl_get_array_element(a_type_tail);
+      b_type_tail = glsl_get_array_element(b_type_tail);
+   }
+
+   if (!glsl_type_is_vector_or_scalar(a_type_tail) ||
+       !glsl_type_is_vector_or_scalar(b_type_tail))
+      return false;
+
+   if (glsl_get_base_type(a->type) != glsl_get_base_type(b->type))
+      return false;
+
+   assert(a->data.mode == b->data.mode);
+   if (shader->info.stage == MESA_SHADER_FRAGMENT &&
+       a->data.mode == nir_var_shader_in &&
+       a->data.interpolation != b->data.interpolation)
+      return false;
+
+   return true;
+}
+
+static bool
+create_new_io_vars(nir_shader *shader, struct exec_list *io_list,
+                   nir_variable *old_vars[MAX_VARYINGS_INCL_PATCH][4],
+                   nir_variable *new_vars[MAX_VARYINGS_INCL_PATCH][4])
+{
+   if (exec_list_is_empty(io_list))
+      return false;
+
+   nir_foreach_variable(var, io_list) {
+      if (variable_can_rewrite(var)) {
+         unsigned loc = var->data.location - VARYING_SLOT_VAR0;
+         unsigned frac = var->data.location_frac;
+         old_vars[loc][frac] = var;
+      }
+   }
+
+   bool merged_any_vars = false;
+
+   /* We don't handle combining vars of different type e.g. different array
+    * lengths.
+    */
+   for (unsigned loc = 0; loc < MAX_VARYINGS_INCL_PATCH; loc++) {
+      unsigned frac = 0;
+      while (frac < 4) {
+         nir_variable *first_var = old_vars[loc][frac];
+         if (!first_var) {
+            frac++;
+            continue;
+         }
+
+         int first = frac;
+         bool found_merge = false;
+
+         while (frac < 4) {
+            nir_variable *var = old_vars[loc][frac];
+            if (!var)
+               break;
+
+            if (var != first_var) {
+               if (!variables_can_merge(shader, first_var, var))
+                  break;
+
+               found_merge = true;
+            }
+
+            const unsigned num_components =
+               glsl_get_components(glsl_without_array(var->type));
+
+            /* We had better not have any overlapping vars */
+            for (unsigned i = 1; i < num_components; i++)
+               assert(old_vars[loc][frac + i] == NULL);
+
+            frac += num_components;
+         }
+
+         if (!found_merge)
+            continue;
+
+         merged_any_vars = true;
+
+         nir_variable *var = nir_variable_clone(old_vars[loc][first], shader);
+         var->data.location_frac = first;
+         var->type = resize_array_vec_type(var->type, frac - first);
+
+         nir_shader_add_variable(shader, var);
+         for (unsigned i = first; i < frac; i++)
+            new_vars[loc][i] = var;
+      }
+   }
+
+   return merged_any_vars;
+}
+
+static nir_deref_instr *
+build_array_deref_of_new_var(nir_builder *b, nir_variable *new_var,
+                             nir_deref_instr *leader)
+{
+   if (leader->deref_type == nir_deref_type_var)
+      return nir_build_deref_var(b, new_var);
+
+   nir_deref_instr *parent =
+      build_array_deref_of_new_var(b, new_var, nir_deref_instr_parent(leader));
+
+   return nir_build_deref_follower(b, parent, leader);
+}
+
+static bool
+nir_lower_io_to_vector_impl(nir_function_impl *impl, nir_variable_mode modes)
+{
+   assert(!(modes & ~(nir_var_shader_in | nir_var_shader_out)));
+
+   nir_builder b;
+   nir_builder_init(&b, impl);
+
+   nir_metadata_require(impl, nir_metadata_dominance);
+
+   nir_shader *shader = impl->function->shader;
+   nir_variable *old_inputs[MAX_VARYINGS_INCL_PATCH][4] = {0};
+   nir_variable *new_inputs[MAX_VARYINGS_INCL_PATCH][4] = {0};
+   nir_variable *old_outputs[MAX_VARYINGS_INCL_PATCH][4] = {0};
+   nir_variable *new_outputs[MAX_VARYINGS_INCL_PATCH][4] = {0};
+
+   if (modes & nir_var_shader_in) {
+      /* Vertex shaders support overlapping inputs.  We don't do those */
+      assert(b.shader->info.stage != MESA_SHADER_VERTEX);
+
+      /* If we don't actually merge any variables, remove that bit from modes
+       * so we don't bother doing extra non-work.
+       */
+      if (!create_new_io_vars(shader, &shader->inputs,
+                              old_inputs, new_inputs))
+         modes &= ~nir_var_shader_in;
+   }
+
+   if (modes & nir_var_shader_out) {
+      /* Fragment shader outputs are always vec4.  You shouldn't have
+       * scalarized them and it doesn't make sense to vectorize them.
+       */
+      assert(b.shader->info.stage != MESA_SHADER_FRAGMENT);
+
+      /* If we don't actually merge any variables, remove that bit from modes
+       * so we don't bother doing extra non-work.
+       */
+      if (!create_new_io_vars(shader, &shader->outputs,
+                              old_outputs, new_outputs))
+         modes &= ~nir_var_shader_out;
+   }
+
+   if (!modes)
+      return false;
+
+   bool progress = false;
+
+   /* Actually lower all the IO load/store intrinsics.  Load instructions are
+    * lowered to a vector load and an ALU instruction to grab the channels we
+    * want.  Outputs are lowered to a write-masked store of the vector output.
+    * For non-TCS outputs, we then run nir_lower_io_to_temporaries at the end
+    * to clean up the partial writes.
+    */
+   nir_foreach_block(block, impl) {
+      nir_foreach_instr_safe(instr, block) {
+         if (instr->type != nir_instr_type_intrinsic)
+            continue;
+
+         nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+
+         switch (intrin->intrinsic) {
+         case nir_intrinsic_load_deref:
+         case nir_intrinsic_interp_deref_at_centroid:
+         case nir_intrinsic_interp_deref_at_sample:
+         case nir_intrinsic_interp_deref_at_offset: {
+            nir_deref_instr *old_deref = nir_src_as_deref(intrin->src[0]);
+            if (!(old_deref->mode & modes))
+               break;
+
+            if (old_deref->mode == nir_var_shader_out)
+               assert(b.shader->info.stage == MESA_SHADER_TESS_CTRL);
+
+            nir_variable *old_var = nir_deref_instr_get_variable(old_deref);
+            if (old_var->data.location < VARYING_SLOT_VAR0)
+               break;
+
+            const unsigned loc = old_var->data.location - VARYING_SLOT_VAR0;
+            const unsigned old_frac = old_var->data.location_frac;
+            nir_variable *new_var = old_deref->mode == nir_var_shader_in ?
+                                    new_inputs[loc][old_frac] :
+                                    new_outputs[loc][old_frac];
+            if (!new_var)
+               break;
+
+            assert(new_var->data.location == VARYING_SLOT_VAR0 + loc);
+            const unsigned new_frac = new_var->data.location_frac;
+
+            nir_component_mask_t vec4_comp_mask =
+               ((1 << intrin->num_components) - 1) << old_frac;
+
+            b.cursor = nir_before_instr(&intrin->instr);
+
+            /* Rewrite the load to use the new variable and only select a
+             * portion of the result.
+             */
+            nir_deref_instr *new_deref =
+               build_array_deref_of_new_var(&b, new_var, old_deref);
+            assert(glsl_type_is_vector(new_deref->type));
+            nir_instr_rewrite_src(&intrin->instr, &intrin->src[0],
+                                  nir_src_for_ssa(&new_deref->dest.ssa));
+
+            intrin->num_components =
+               glsl_get_components(new_deref->type);
+            intrin->dest.ssa.num_components = intrin->num_components;
+
+            b.cursor = nir_after_instr(&intrin->instr);
+
+            nir_ssa_def *new_vec = nir_channels(&b, &intrin->dest.ssa,
+                                                vec4_comp_mask >> new_frac);
+            nir_ssa_def_rewrite_uses_after(&intrin->dest.ssa,
+                                           nir_src_for_ssa(new_vec),
+                                           new_vec->parent_instr);
+
+            progress = true;
+            break;
+         }
+
+         case nir_intrinsic_store_deref: {
+            nir_deref_instr *old_deref = nir_src_as_deref(intrin->src[0]);
+            if (old_deref->mode != nir_var_shader_out)
+               break;
+
+            nir_variable *old_var = nir_deref_instr_get_variable(old_deref);
+            if (old_var->data.location < VARYING_SLOT_VAR0)
+               break;
+
+            const unsigned loc = old_var->data.location - VARYING_SLOT_VAR0;
+            const unsigned old_frac = old_var->data.location_frac;
+            nir_variable *new_var = new_outputs[loc][old_frac];
+            if (!new_var)
+               break;
+
+            assert(new_var->data.location == VARYING_SLOT_VAR0 + loc);
+            const unsigned new_frac = new_var->data.location_frac;
+
+            b.cursor = nir_before_instr(&intrin->instr);
+
+            /* Rewrite the store to be a masked store to the new variable */
+            nir_deref_instr *new_deref =
+               build_array_deref_of_new_var(&b, new_var, old_deref);
+            assert(glsl_type_is_vector(new_deref->type));
+            nir_instr_rewrite_src(&intrin->instr, &intrin->src[0],
+                                  nir_src_for_ssa(&new_deref->dest.ssa));
+
+            intrin->num_components =
+               glsl_get_components(new_deref->type);
+
+            nir_component_mask_t old_wrmask = nir_intrinsic_write_mask(intrin);
+
+            assert(intrin->src[1].is_ssa);
+            nir_ssa_def *old_value = intrin->src[1].ssa;
+            nir_ssa_def *comps[4];
+            for (unsigned c = 0; c < intrin->num_components; c++) {
+               if (new_frac + c >= old_frac &&
+                   (old_wrmask & 1 << (new_frac + c - old_frac))) {
+                  comps[c] = nir_channel(&b, old_value,
+                                         new_frac + c - old_frac);
+               } else {
+                  comps[c] = nir_ssa_undef(&b, old_value->num_components,
+                                               old_value->bit_size);
+               }
+            }
+            nir_ssa_def *new_value = nir_vec(&b, comps, intrin->num_components);
+            nir_instr_rewrite_src(&intrin->instr, &intrin->src[1],
+                                  nir_src_for_ssa(new_value));
+
+            nir_intrinsic_set_write_mask(intrin,
+                                         old_wrmask << (old_frac - new_frac));
+
+            progress = true;
+            break;
+         }
+
+         default:
+            break;
+         }
+      }
+   }
+
+   if (progress) {
+      nir_metadata_preserve(impl, nir_metadata_block_index |
+                                  nir_metadata_dominance);
+   }
+
+   return progress;
+}
+
+bool
+nir_lower_io_to_vector(nir_shader *shader, nir_variable_mode modes)
+{
+   bool progress = false;
+
+   nir_foreach_function(function, shader) {
+      if (function->impl)
+         progress |= nir_lower_io_to_vector_impl(function->impl, modes);
+   }
+
+   return progress;
+}