nir: add new helper passes that lower uniforms to literals

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6955>

src/compiler/Makefile.sources

@@ -227,6 +227,7 @@ NIR_FILES = \
 	nir/nir_gather_xfb_info.c \
 	nir/nir_gs_count_vertices.c \
 	nir/nir_inline_functions.c \
+        nir/nir_inline_uniforms.c \
 	nir/nir_instr_set.c \
 	nir/nir_instr_set.h \
 	nir/nir_linking_helpers.c \

src/compiler/nir/meson.build

@@ -107,6 +107,7 @@ files_libnir = files(
   'nir_gather_xfb_info.c',
   'nir_gs_count_vertices.c',
   'nir_inline_functions.c',
+  'nir_inline_uniforms.c',
   'nir_instr_set.c',
   'nir_instr_set.h',
   'nir_linking_helpers.c',

src/compiler/nir/nir.h

@@ -4124,6 +4124,11 @@ void nir_inline_function_impl(struct nir_builder *b,
                               struct hash_table *shader_var_remap);
 bool nir_inline_functions(nir_shader *shader);
 
+void nir_find_inlinable_uniforms(nir_shader *shader);
+void nir_inline_uniforms(nir_shader *shader, unsigned num_uniforms,
+                         const uint32_t *uniform_values,
+                         const uint16_t *uniform_dw_offsets);
+
 bool nir_propagate_invariant(nir_shader *shader);
 
 void nir_lower_var_copy_instr(nir_intrinsic_instr *copy, nir_shader *shader);

src/compiler/nir/nir_inline_uniforms.c

@@ -0,0 +1,202 @@
+/*
+ * Copyright © 2020 Advanced Micro Devices, Inc.
+ *
+ * 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.
+ */
+
+/* These passes enable converting uniforms to literals when it's profitable,
+ * effectively inlining uniform values in the IR. The main benefit is register
+ * usage decrease leading to better SMT (hyperthreading). It's accomplished
+ * by targetting uniforms that determine whether a conditional branch is
+ * taken.
+ *
+ * Only uniforms used in if conditions are analyzed.
+ *
+ * nir_find_inlinable_uniforms finds uniforms that can be inlined and stores
+ * that information in shader_info.
+ *
+ * nir_inline_uniforms inlines uniform values.
+ *
+ * (uniforms must be lowered to load_ubo before calling this)
+ */
+
+#include "compiler/nir/nir_builder.h"
+
+/* Maximum value in shader_info::inlinable_uniform_dw_offsets[] */
+#define MAX_OFFSET (UINT16_MAX * 4)
+
+static bool
+src_only_uses_uniforms(const nir_src *src, struct set **uni_offsets)
+{
+   if (!src->is_ssa)
+      return false;
+
+   nir_instr *instr = src->ssa->parent_instr;
+
+   switch (instr->type) {
+   case nir_instr_type_alu: {
+      /* Return true if all sources return true. */
+      /* TODO: Swizzles are ignored, so vectors can prevent inlining. */
+      nir_alu_instr *alu = nir_instr_as_alu(instr);
+      for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
+         if (!src_only_uses_uniforms(&alu->src[i].src, uni_offsets))
+             return false;
+      }
+      return true;
+   }
+
+   case nir_instr_type_intrinsic: {
+      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+      /* Return true if the intrinsic loads from UBO 0 with a constant
+       * offset.
+       */
+      if (intr->intrinsic == nir_intrinsic_load_ubo &&
+          nir_src_is_const(intr->src[0]) &&
+          nir_src_as_uint(intr->src[0]) == 0 &&
+          nir_src_is_const(intr->src[1]) &&
+          nir_src_as_uint(intr->src[1]) <= MAX_OFFSET &&
+          /* TODO: Can't handle vectors and other bit sizes for now. */
+          /* UBO loads should be scalarized. */
+          intr->dest.ssa.num_components == 1 &&
+          intr->dest.ssa.bit_size == 32) {
+         /* Record the uniform offset. */
+         if (!*uni_offsets)
+            *uni_offsets = _mesa_set_create_u32_keys(NULL);
+
+         /* Add 1 because the set doesn't allow NULL keys. */
+         _mesa_set_add(*uni_offsets,
+                       (void*)(uintptr_t)(nir_src_as_uint(intr->src[1]) + 1));
+         return true;
+      }
+      return false;
+   }
+
+   case nir_instr_type_load_const:
+      /* Always return true for constants. */
+      return true;
+
+   default:
+      return false;
+   }
+}
+
+void
+nir_find_inlinable_uniforms(nir_shader *shader)
+{
+   struct set *uni_offsets = NULL;
+
+   nir_foreach_function(function, shader) {
+      if (function->impl) {
+         foreach_list_typed(nir_cf_node, node, node, &function->impl->body) {
+            switch (node->type) {
+            case nir_cf_node_if: {
+               const nir_src *cond = &nir_cf_node_as_if(node)->condition;
+               struct set *found_offsets = NULL;
+
+               if (src_only_uses_uniforms(cond, &found_offsets) &&
+                   found_offsets) {
+                  /* All uniforms are lowerable. Save uniform offsets. */
+                  set_foreach(found_offsets, entry) {
+                     if (!uni_offsets)
+                        uni_offsets = _mesa_set_create_u32_keys(NULL);
+
+                     _mesa_set_add(uni_offsets, entry->key);
+                  }
+               }
+               if (found_offsets)
+                  _mesa_set_destroy(found_offsets, NULL);
+               break;
+            }
+
+            case nir_cf_node_loop:
+               /* TODO: handle loops if we want to unroll them at draw time */
+               break;
+
+            default:
+               break;
+            }
+         }
+      }
+   }
+
+   if (uni_offsets) {
+      unsigned num = 0;
+
+      set_foreach(uni_offsets, entry) {
+         /* Subtract 1 because all keys are + 1. */
+         uint32_t offset = (uintptr_t)entry->key - 1;
+         assert(offset < MAX_OFFSET);
+
+         if (num < MAX_INLINABLE_UNIFORMS)
+            shader->info.inlinable_uniform_dw_offsets[num++] = offset / 4;
+      }
+      shader->info.num_inlinable_uniforms = num;
+      _mesa_set_destroy(uni_offsets, NULL);
+   }
+}
+
+void
+nir_inline_uniforms(nir_shader *shader, unsigned num_uniforms,
+                    const uint32_t *uniform_values,
+                    const uint16_t *uniform_dw_offsets)
+{
+   if (!num_uniforms)
+      return;
+
+   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);
+
+               /* Only replace UBO 0 with constant offsets. */
+               if (intr->intrinsic == nir_intrinsic_load_ubo &&
+                   nir_src_is_const(intr->src[0]) &&
+                   nir_src_as_uint(intr->src[0]) == 0 &&
+                   nir_src_is_const(intr->src[1]) &&
+                   /* TODO: Can't handle vectors and other bit sizes for now. */
+                   /* UBO loads should be scalarized. */
+                   intr->dest.ssa.num_components == 1 &&
+                   intr->dest.ssa.bit_size == 32) {
+                  uint64_t offset = nir_src_as_uint(intr->src[1]);
+
+                  for (unsigned i = 0; i < num_uniforms; i++) {
+                     if (offset == uniform_dw_offsets[i] * 4) {
+                        b.cursor = nir_before_instr(&intr->instr);
+                        nir_ssa_def *def = nir_imm_int(&b, uniform_values[i]);
+                        nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(def));
+                        nir_instr_remove(&intr->instr);
+                        break;
+                     }
+                  }
+               }
+            }
+         }
+
+         nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                               nir_metadata_dominance);
+      }
+   }
+}

src/compiler/shader_info.h

@@ -32,6 +32,8 @@
 extern "C" {
 #endif
 
+#define MAX_INLINABLE_UNIFORMS 4
+
 struct spirv_supported_capabilities {
    bool address;
    bool atomic_storage;
@@ -165,6 +167,9 @@ typedef struct shader_info {
    /* SPV_KHR_float_controls: execution mode for floating point ops */
    uint16_t float_controls_execution_mode;
 
+   uint16_t inlinable_uniform_dw_offsets[MAX_INLINABLE_UNIFORMS];
+   uint8_t num_inlinable_uniforms:4;
+
    /* The size of the gl_ClipDistance[] array, if declared. */
    uint8_t clip_distance_array_size:4;