nir: Add a new subgroups lowering pass

This commit pulls nir_lower_read_invocations_to_scalar along with most
of the guts of nir_opt_intrinsics (which mostly does subgroup lowering)
into a new nir_lower_subgroups pass.  There are various other bits of
subgroup lowering that we're going to want to do so it makes a bit more
sense to keep it all together in one pass.  We also move it in i965 to
happen after nir_lower_system_values to ensure that because we want to
handle the subgroup mask system value intrinsics here.

Reviewed-by: Iago Toral Quiroga <[email protected]>

1 files changed, 184 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_lower_subgroups.c b/src/compiler/nir/nir_lower_subgroups.c
new file mode 100644
index 00000000000..0d11dc9c23a
--- /dev/null
+++ b/src/compiler/nir/nir_lower_subgroups.c
@@ -0,0 +1,184 @@
+/*
+ * Copyright © 2017 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"
+
+/**
+ * \file nir_opt_intrinsics.c
+ */
+
+static nir_ssa_def *
+lower_read_invocation_to_scalar(nir_builder *b, nir_intrinsic_instr *intrin)
+{
+   /* This is safe to call on scalar things but it would be silly */
+   assert(intrin->dest.ssa.num_components > 1);
+
+   nir_ssa_def *value = nir_ssa_for_src(b, intrin->src[0],
+                                           intrin->num_components);
+   nir_ssa_def *reads[4];
+
+   for (unsigned i = 0; i < intrin->num_components; i++) {
+      nir_intrinsic_instr *chan_intrin =
+         nir_intrinsic_instr_create(b->shader, intrin->intrinsic);
+      nir_ssa_dest_init(&chan_intrin->instr, &chan_intrin->dest,
+                        1, intrin->dest.ssa.bit_size, NULL);
+      chan_intrin->num_components = 1;
+
+      /* value */
+      chan_intrin->src[0] = nir_src_for_ssa(nir_channel(b, value, i));
+      /* invocation */
+      if (intrin->intrinsic == nir_intrinsic_read_invocation)
+         nir_src_copy(&chan_intrin->src[1], &intrin->src[1], chan_intrin);
+
+      nir_builder_instr_insert(b, &chan_intrin->instr);
+
+      reads[i] = &chan_intrin->dest.ssa;
+   }
+
+   return nir_vec(b, reads, intrin->num_components);
+}
+
+static nir_ssa_def *
+high_subgroup_mask(nir_builder *b,
+                   nir_ssa_def *count,
+                   uint64_t base_mask)
+{
+   /* group_mask could probably be calculated more efficiently but we want to
+    * be sure not to shift by 64 if the subgroup size is 64 because the GLSL
+    * shift operator is undefined in that case. In any case if we were worried
+    * about efficency this should probably be done further down because the
+    * subgroup size is likely to be known at compile time.
+    */
+   nir_ssa_def *subgroup_size = nir_load_subgroup_size(b);
+   nir_ssa_def *all_bits = nir_imm_int64(b, ~0ull);
+   nir_ssa_def *shift = nir_isub(b, nir_imm_int(b, 64), subgroup_size);
+   nir_ssa_def *group_mask = nir_ushr(b, all_bits, shift);
+   nir_ssa_def *higher_bits = nir_ishl(b, nir_imm_int64(b, base_mask), count);
+
+   return nir_iand(b, higher_bits, group_mask);
+}
+
+static nir_ssa_def *
+lower_subgroups_intrin(nir_builder *b, nir_intrinsic_instr *intrin,
+                       const nir_lower_subgroups_options *options)
+{
+   switch (intrin->intrinsic) {
+   case nir_intrinsic_vote_any:
+   case nir_intrinsic_vote_all:
+      if (options->lower_vote_trivial)
+         return nir_ssa_for_src(b, intrin->src[0], 1);
+      break;
+
+   case nir_intrinsic_vote_eq:
+      if (options->lower_vote_trivial)
+         return nir_imm_int(b, NIR_TRUE);
+      break;
+
+   case nir_intrinsic_read_invocation:
+   case nir_intrinsic_read_first_invocation:
+      if (options->lower_to_scalar && intrin->num_components > 1)
+         return lower_read_invocation_to_scalar(b, intrin);
+      break;
+
+   case nir_intrinsic_load_subgroup_eq_mask:
+   case nir_intrinsic_load_subgroup_ge_mask:
+   case nir_intrinsic_load_subgroup_gt_mask:
+   case nir_intrinsic_load_subgroup_le_mask:
+   case nir_intrinsic_load_subgroup_lt_mask: {
+      if (!options->lower_subgroup_masks)
+         return NULL;
+
+      nir_ssa_def *count = nir_load_subgroup_invocation(b);
+
+      switch (intrin->intrinsic) {
+      case nir_intrinsic_load_subgroup_eq_mask:
+         return nir_ishl(b, nir_imm_int64(b, 1ull), count);
+      case nir_intrinsic_load_subgroup_ge_mask:
+         return high_subgroup_mask(b, count, ~0ull);
+      case nir_intrinsic_load_subgroup_gt_mask:
+         return high_subgroup_mask(b, count, ~1ull);
+      case nir_intrinsic_load_subgroup_le_mask:
+         return nir_inot(b, nir_ishl(b, nir_imm_int64(b, ~1ull), count));
+      case nir_intrinsic_load_subgroup_lt_mask:
+         return nir_inot(b, nir_ishl(b, nir_imm_int64(b, ~0ull), count));
+      default:
+         unreachable("you seriously can't tell this is unreachable?");
+      }
+      break;
+   }
+   default:
+      break;
+   }
+
+   return NULL;
+}
+
+static bool
+lower_subgroups_impl(nir_function_impl *impl,
+                     const nir_lower_subgroups_options *options)
+{
+   nir_builder b;
+   nir_builder_init(&b, impl);
+   bool progress = false;
+
+   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);
+         b.cursor = nir_before_instr(instr);
+
+         nir_ssa_def *lower = lower_subgroups_intrin(&b, intrin, options);
+         if (!lower)
+            continue;
+
+         nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(lower));
+         nir_instr_remove(instr);
+         progress = true;
+      }
+   }
+
+   return progress;
+}
+
+bool
+nir_lower_subgroups(nir_shader *shader,
+                    const nir_lower_subgroups_options *options)
+{
+   bool progress = false;
+
+   nir_foreach_function(function, shader) {
+      if (!function->impl)
+         continue;
+
+      if (lower_subgroups_impl(function->impl, options)) {
+         progress = true;
+         nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                               nir_metadata_dominance);
+      }
+   }
+
+   return progress;
+}