nir: Add a lowering pass for adding source modifiers where possible

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/glsl/Makefile.sources

@@ -27,6 +27,7 @@ NIR_FILES = \
 	$(GLSL_SRCDIR)/nir/nir_lower_io.c \
 	$(GLSL_SRCDIR)/nir/nir_lower_samplers.cpp \
 	$(GLSL_SRCDIR)/nir/nir_lower_system_values.c \
+	$(GLSL_SRCDIR)/nir/nir_lower_to_source_mods.c \
 	$(GLSL_SRCDIR)/nir/nir_lower_variables.c \
 	$(GLSL_SRCDIR)/nir/nir_lower_vec_to_movs.c \
 	$(GLSL_SRCDIR)/nir/nir_metadata.c \

src/glsl/nir/nir.h

@@ -1389,6 +1389,7 @@ void nir_lower_samplers(nir_shader *shader,
 void nir_lower_system_values(nir_shader *shader);
 
 void nir_lower_atomics(nir_shader *shader);
+void nir_lower_to_source_mods(nir_shader *shader);
 
 void nir_live_variables_impl(nir_function_impl *impl);
 bool nir_ssa_defs_interfere(nir_ssa_def *a, nir_ssa_def *b);

src/glsl/nir/nir_lower_to_source_mods.c

+/*
+ * Copyright © 2014 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 (jason@jlekstrand.net)
+ *
+ */
+
+#include "nir.h"
+
+/*
+ * This pass lowers the neg, abs, and sat operations to source modifiers on
+ * ALU operations to make things nicer for the backend.  It's just much
+ * easier to not have them when we're doing optimizations.
+ */
+
+static bool
+nir_lower_to_source_mods_block(nir_block *block, void *state)
+{
+   nir_foreach_instr(block, instr) {
+      if (instr->type != nir_instr_type_alu)
+         continue;
+
+      nir_alu_instr *alu = nir_instr_as_alu(instr);
+
+      for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
+         if (!alu->src[i].src.is_ssa)
+            continue;
+
+         if (alu->src[i].src.ssa->parent_instr->type != nir_instr_type_alu)
+            continue;
+
+         nir_alu_instr *parent = nir_instr_as_alu(alu->src[i].src.ssa->parent_instr);
+
+         if (parent->dest.saturate)
+            continue;
+
+         switch (nir_op_infos[alu->op].input_types[i]) {
+         case nir_type_float:
+            if (parent->op != nir_op_fmov)
+               continue;
+            break;
+         case nir_type_int:
+            if (parent->op != nir_op_imov)
+               continue;
+            break;
+         default:
+            continue;
+         }
+
+         nir_instr_rewrite_src(instr, &alu->src[i].src, parent->src[0].src);
+         if (alu->src[i].abs) {
+            /* abs trumps both neg and abs, do nothing */
+         } else {
+            alu->src[i].negate = (alu->src[i].negate != parent->src[0].negate);
+            alu->src[i].abs |= parent->src[0].abs;
+         }
+
+         for (int j = 0; j < 4; ++j) {
+            if (!nir_alu_instr_channel_used(alu, i, j))
+               continue;
+            alu->src[i].swizzle[j] = parent->src[0].swizzle[alu->src[i].swizzle[j]];
+         }
+
+         if (parent->dest.dest.ssa.uses->entries == 0 &&
+             parent->dest.dest.ssa.if_uses->entries == 0)
+            nir_instr_remove(&parent->instr);
+      }
+
+      switch (alu->op) {
+      case nir_op_fsat:
+         alu->op = nir_op_fmov;
+         alu->dest.saturate = true;
+         break;
+      case nir_op_ineg:
+         alu->op = nir_op_imov;
+         alu->src[0].negate = !alu->src[0].negate;
+         break;
+      case nir_op_fneg:
+         alu->op = nir_op_fmov;
+         alu->src[0].negate = !alu->src[0].negate;
+         break;
+      case nir_op_iabs:
+         alu->op = nir_op_imov;
+         alu->src[0].abs = true;
+         alu->src[0].negate = false;
+         break;
+      case nir_op_fabs:
+         alu->op = nir_op_fmov;
+         alu->src[0].abs = true;
+         alu->src[0].negate = false;
+         break;
+      default:
+         break;
+      }
+
+      /* We've covered sources.  Now we're going to try and saturate the
+       * destination if we can.
+       */
+
+      if (!alu->dest.dest.is_ssa)
+         continue;
+
+      if (alu->dest.dest.ssa.if_uses->entries != 0)
+         continue;
+
+      bool all_children_are_sat = true;
+      struct set_entry *entry;
+      set_foreach(alu->dest.dest.ssa.uses, entry) {
+         const nir_instr *child = entry->key;
+         if (child->type != nir_instr_type_alu) {
+            all_children_are_sat = false;
+            continue;
+         }
+
+         nir_alu_instr *child_alu = nir_instr_as_alu(child);
+         if (child_alu->src[0].negate || child_alu->src[0].abs) {
+            all_children_are_sat = false;
+            continue;
+         }
+
+         if (child_alu->op != nir_op_fsat &&
+             !(child_alu->op == nir_op_fmov && child_alu->dest.saturate)) {
+            all_children_are_sat = false;
+            continue;
+         }
+      }
+
+      if (!all_children_are_sat)
+         continue;
+
+      alu->dest.saturate = true;
+
+      set_foreach(alu->dest.dest.ssa.uses, entry) {
+         nir_alu_instr *child_alu = nir_instr_as_alu((nir_instr *)entry->key);
+         child_alu->op = nir_op_fmov;
+         child_alu->dest.saturate = false;
+         /* We could propagate the dest of our instruction to the
+          * destinations of the uses here.  However, one quick round of
+          * copy propagation will clean that all up and then we don't have
+          * the complexity.
+          */
+      }
+   }
+
+   return true;
+}
+
+static void
+nir_lower_to_source_mods_impl(nir_function_impl *impl)
+{
+   nir_foreach_block(impl, nir_lower_to_source_mods_block, NULL);
+}
+
+void
+nir_lower_to_source_mods(nir_shader *shader)
+{
+   nir_foreach_overload(shader, overload) {
+      if (overload->impl)
+         nir_lower_to_source_mods_impl(overload->impl);
+   }
+}

src/mesa/drivers/dri/i965/brw_fs_nir.cpp

@@ -66,6 +66,11 @@ fs_visitor::emit_nir_code()
 
    nir_remove_dead_variables(nir);
    nir_validate_shader(nir);
+
+   nir_lower_to_source_mods(nir);
+   nir_validate_shader(nir);
+   nir_copy_prop(nir);
+   nir_validate_shader(nir);
    nir_convert_from_ssa(nir);
    nir_validate_shader(nir);
    nir_lower_vec_to_movs(nir);