nir: Add a pass for selectively lowering variables to scratch space

This commit adds new nir_load/store_scratch opcodes which read and write
a virtual scratch space.  It's up to the back-end to figure out what to
do with it and where to put the actual scratch data.

v2: Drop const_index comments (by anholt)

Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 195 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_lower_scratch.c b/src/compiler/nir/nir_lower_scratch.c
new file mode 100644
index 00000000000..df0d3f43124
--- /dev/null
+++ b/src/compiler/nir/nir_lower_scratch.c
@@ -0,0 +1,195 @@
+/*
+ * Copyright © 2016 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 ([email protected])
+ *
+ */
+
+/*
+ * This lowering pass converts references to variables with loads/stores to
+ * scratch space based on a few configurable parameters.
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+#include "nir_deref.h"
+
+static bool
+deref_has_indirect(nir_deref_instr *deref)
+{
+   while (deref->deref_type != nir_deref_type_var) {
+      if (deref->deref_type == nir_deref_type_array &&
+          nir_src_as_const_value(deref->arr.index) == NULL)
+         return true;
+
+      deref = nir_deref_instr_parent(deref);
+   }
+
+   return false;
+}
+
+static void
+lower_load_store(nir_builder *b,
+                 nir_intrinsic_instr *intrin,
+                 glsl_type_size_align_func size_align)
+{
+   b->cursor = nir_before_instr(&intrin->instr);
+
+   nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
+   nir_variable *var = nir_deref_instr_get_variable(deref);
+
+   nir_ssa_def *offset =
+      nir_iadd_imm(b, nir_build_deref_offset(b, deref, size_align),
+                      var->data.location);
+
+   unsigned align, UNUSED size;
+   size_align(deref->type, &size, &align);
+
+   if (intrin->intrinsic == nir_intrinsic_load_deref) {
+      nir_intrinsic_instr *load =
+         nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_scratch);
+      load->num_components = intrin->num_components;
+      load->src[0] = nir_src_for_ssa(offset);
+      nir_intrinsic_set_align(load, align, 0);
+      nir_ssa_dest_init(&load->instr, &load->dest,
+                        intrin->dest.ssa.num_components,
+                        intrin->dest.ssa.bit_size, NULL);
+      nir_builder_instr_insert(b, &load->instr);
+
+      nir_ssa_def *value = &load->dest.ssa;
+      if (glsl_type_is_boolean(deref->type))
+         value = nir_b2i32(b, value);
+
+      nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
+                               nir_src_for_ssa(&load->dest.ssa));
+   } else {
+      assert(intrin->intrinsic == nir_intrinsic_store_deref);
+
+      assert(intrin->src[1].is_ssa);
+      nir_ssa_def *value = intrin->src[1].ssa;
+      if (glsl_type_is_boolean(deref->type))
+         value = nir_i2b(b, value);
+
+      nir_intrinsic_instr *store =
+         nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_scratch);
+      store->num_components = intrin->num_components;
+      store->src[0] = nir_src_for_ssa(value);
+      store->src[1] = nir_src_for_ssa(offset);
+      nir_intrinsic_set_write_mask(store, nir_intrinsic_write_mask(intrin));
+      nir_intrinsic_set_align(store, align, 0);
+      nir_builder_instr_insert(b, &store->instr);
+   }
+
+   nir_instr_remove(&intrin->instr);
+   nir_deref_instr_remove_if_unused(deref);
+}
+
+bool
+nir_lower_vars_to_scratch(nir_shader *shader,
+                          nir_variable_mode modes,
+                          int size_threshold,
+                          glsl_type_size_align_func size_align)
+{
+   /* First, we walk the instructions and flag any variables we want to lower
+    * by removing them from their respective list and setting the mode to 0.
+    */
+   nir_foreach_function(function, shader) {
+      nir_foreach_block(block, function->impl) {
+         nir_foreach_instr(instr, block) {
+            if (instr->type != nir_instr_type_intrinsic)
+               continue;
+
+            nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+            if (intrin->intrinsic != nir_intrinsic_load_deref &&
+                intrin->intrinsic != nir_intrinsic_store_deref)
+               continue;
+
+            nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
+            if (!(deref->mode & modes))
+               continue;
+
+            if (!deref_has_indirect(nir_src_as_deref(intrin->src[0])))
+               continue;
+
+            nir_variable *var = nir_deref_instr_get_variable(deref);
+
+            /* We set var->mode to 0 to indicate that a variable will be moved
+             * to scratch.  Don't assign a scratch location twice.
+             */
+            if (var->data.mode == 0)
+               continue;
+
+            unsigned var_size, var_align;
+            size_align(var->type, &var_size, &var_align);
+            if (var_size <= size_threshold)
+               continue;
+
+            /* Remove it from its list */
+            exec_node_remove(&var->node);
+            /* Invalid mode used to flag "moving to scratch" */
+            var->data.mode = 0;
+
+            var->data.location = ALIGN_POT(shader->scratch_size, var_align);
+            shader->scratch_size = var->data.location + var_size;
+         }
+      }
+   }
+
+   bool progress = false;
+   nir_foreach_function(function, shader) {
+      if (!function->impl)
+         continue;
+
+      nir_builder build;
+      nir_builder_init(&build, function->impl);
+
+      bool impl_progress = false;
+      nir_foreach_block(block, function->impl) {
+         nir_foreach_instr_safe(instr, block) {
+            if (instr->type != nir_instr_type_intrinsic)
+               continue;
+
+            nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+            if (intrin->intrinsic != nir_intrinsic_load_deref &&
+                intrin->intrinsic != nir_intrinsic_store_deref)
+               continue;
+
+            nir_variable *var = nir_intrinsic_get_var(intrin, 0);
+            /* Variables flagged for lowering above have mode == 0 */
+            if (!var || var->data.mode)
+               continue;
+
+            lower_load_store(&build, intrin, size_align);
+            impl_progress = true;
+         }
+      }
+
+      if (impl_progress) {
+         progress = true;
+         nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                               nir_metadata_dominance);
+      }
+   }
+
+   return progress;
+}