nir: Add an IO scalarizing pass using the intrinsic's first_component.

vc4 wants to have per-scalar IO load/stores so that dead code elimination
can happen on a more granular basis, which it has been doing in the
backend using a multiplication by 4 of the intrinsic's driver_location.
We can represent it properly in the NIR using the first_component field,
though.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/Makefile.sources

@@ -203,6 +203,7 @@ NIR_FILES = \
 	nir/nir_lower_indirect_derefs.c \
 	nir/nir_lower_io.c \
 	nir/nir_lower_io_to_temporaries.c \
+	nir/nir_lower_io_to_scalar.c \
 	nir/nir_lower_io_types.c \
 	nir/nir_lower_passthrough_edgeflags.c \
 	nir/nir_lower_phis_to_scalar.c \

src/compiler/nir/nir.h

@@ -2395,6 +2395,7 @@ void nir_lower_alu_to_scalar(nir_shader *shader);
 void nir_lower_load_const_to_scalar(nir_shader *shader);
 
 void nir_lower_phis_to_scalar(nir_shader *shader);
+void nir_lower_io_to_scalar(nir_shader *shader, nir_variable_mode mask);
 
 void nir_lower_samplers(nir_shader *shader,
                         const struct gl_shader_program *shader_program);

src/compiler/nir/nir_lower_io_to_scalar.c

@@ -0,0 +1,129 @@
+/*
+ * Copyright © 2016 Broadcom
+ *
+ * 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"
+
+/** @file nir_lower_io_to_scalar.c
+ *
+ * Replaces nir_load_input/nir_store_output operations with num_components !=
+ * 1 with individual per-channel operations.
+ */
+
+static void
+lower_load_input_to_scalar(nir_builder *b, nir_intrinsic_instr *intr)
+{
+   b->cursor = nir_before_instr(&intr->instr);
+
+   assert(intr->dest.is_ssa);
+
+   nir_ssa_def *loads[4];
+
+   for (unsigned i = 0; i < intr->num_components; i++) {
+      nir_intrinsic_instr *chan_intr =
+         nir_intrinsic_instr_create(b->shader, intr->intrinsic);
+      nir_ssa_dest_init(&chan_intr->instr, &chan_intr->dest,
+                        1, intr->dest.ssa.bit_size, NULL);
+      chan_intr->num_components = 1;
+
+      nir_intrinsic_set_base(chan_intr, nir_intrinsic_base(intr));
+      nir_intrinsic_set_component(chan_intr, nir_intrinsic_component(intr) + i);
+      /* offset */
+      chan_intr->src[0] = intr->src[0];
+
+      nir_builder_instr_insert(b, &chan_intr->instr);
+
+      loads[i] = &chan_intr->dest.ssa;
+   }
+
+   nir_ssa_def_rewrite_uses(&intr->dest.ssa,
+                            nir_src_for_ssa(nir_vec(b, loads,
+                                                    intr->num_components)));
+   nir_instr_remove(&intr->instr);
+}
+
+static void
+lower_store_output_to_scalar(nir_builder *b, nir_intrinsic_instr *intr)
+{
+   b->cursor = nir_before_instr(&intr->instr);
+
+   nir_ssa_def *value = nir_ssa_for_src(b, intr->src[0], intr->num_components);
+
+   for (unsigned i = 0; i < intr->num_components; i++) {
+      if (!(nir_intrinsic_write_mask(intr) & (1 << i)))
+         continue;
+
+      nir_intrinsic_instr *chan_intr =
+         nir_intrinsic_instr_create(b->shader, intr->intrinsic);
+      chan_intr->num_components = 1;
+
+      nir_intrinsic_set_base(chan_intr, nir_intrinsic_base(intr));
+      nir_intrinsic_set_write_mask(chan_intr, 0x1);
+      nir_intrinsic_set_component(chan_intr, nir_intrinsic_component(intr) + i);
+
+      /* value */
+      chan_intr->src[0] = nir_src_for_ssa(nir_channel(b, value, i));
+      /* offset */
+      chan_intr->src[1] = intr->src[1];
+
+      nir_builder_instr_insert(b, &chan_intr->instr);
+   }
+
+   nir_instr_remove(&intr->instr);
+}
+
+void
+nir_lower_io_to_scalar(nir_shader *shader, nir_variable_mode mask)
+{
+   nir_foreach_function(function, shader) {
+      if (function->impl) {
+         nir_builder b;
+         nir_builder_init(&b, function->impl);
+
+         nir_foreach_block(block, function->impl) {
+            nir_foreach_instr_safe(instr, block) {
+               if (instr->type != nir_instr_type_intrinsic)
+                  continue;
+
+               nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+
+               if (intr->num_components == 1)
+                  continue;
+
+               switch (intr->intrinsic) {
+               case nir_intrinsic_load_input:
+                  if (mask & nir_var_shader_in)
+                     lower_load_input_to_scalar(&b, intr);
+                  break;
+               case nir_intrinsic_store_output:
+                  if (mask & nir_var_shader_out)
+                     lower_store_output_to_scalar(&b, intr);
+                  break;
+               default:
+                  break;
+               }
+            }
+         }
+      }
+   }
+}