nir: Add a pass for propagating invariant decorations

This pass is similar to propagate_invariance in the GLSL compiler.  The
real "output" of this pass is that any algebraic operations which are
eventually consumed by an invariant variable get marked as "exact".

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>

3 files changed, 199 insertions, 0 deletions

diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index 5c4ea65b5e9..0ff9b23e4c3 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -231,6 +231,7 @@ NIR_FILES = \
 	nir/nir_phi_builder.c \
 	nir/nir_phi_builder.h \
 	nir/nir_print.c \
+	nir/nir_propagate_invariant.c \
 	nir/nir_remove_dead_variables.c \
 	nir/nir_repair_ssa.c \
 	nir/nir_search.c \
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index ec7b0c7726d..1725ee3de0a 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2290,6 +2290,8 @@ bool nir_lower_returns(nir_shader *shader);
 
 bool nir_inline_functions(nir_shader *shader);
 
+bool nir_propagate_invariant(nir_shader *shader);
+
 void nir_lower_var_copy_instr(nir_intrinsic_instr *copy, void *mem_ctx);
 void nir_lower_var_copies(nir_shader *shader);
 
diff --git a/src/compiler/nir/nir_propagate_invariant.c b/src/compiler/nir/nir_propagate_invariant.c
new file mode 100644
index 00000000000..7b5bd6cce6b
--- /dev/null
+++ b/src/compiler/nir/nir_propagate_invariant.c
@@ -0,0 +1,196 @@
+/*
+ * 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.
+ */
+
+#include "nir.h"
+
+static void
+add_src(nir_src *src, struct set *invariants)
+{
+   if (src->is_ssa) {
+      _mesa_set_add(invariants, src->ssa);
+   } else {
+      _mesa_set_add(invariants, src->reg.reg);
+   }
+}
+
+static bool
+add_src_cb(nir_src *src, void *state)
+{
+   add_src(src, state);
+   return true;
+}
+
+static bool
+dest_is_invariant(nir_dest *dest, struct set *invariants)
+{
+   if (dest->is_ssa) {
+      return _mesa_set_search(invariants, &dest->ssa);
+   } else {
+      return _mesa_set_search(invariants, dest->reg.reg);
+   }
+}
+
+static void
+add_cf_node(nir_cf_node *cf, struct set *invariants)
+{
+   if (cf->type == nir_cf_node_if) {
+      nir_if *if_stmt = nir_cf_node_as_if(cf);
+      add_src(&if_stmt->condition, invariants);
+   }
+
+   if (cf->parent)
+      add_cf_node(cf->parent, invariants);
+}
+
+static void
+add_var(nir_variable *var, struct set *invariants)
+{
+   _mesa_set_add(invariants, var);
+}
+
+static bool
+var_is_invariant(nir_variable *var, struct set * invariants)
+{
+   return var->data.invariant || _mesa_set_search(invariants, var);
+}
+
+static void
+propagate_invariant_instr(nir_instr *instr, struct set *invariants)
+{
+   switch (instr->type) {
+   case nir_instr_type_alu: {
+      nir_alu_instr *alu = nir_instr_as_alu(instr);
+      if (!dest_is_invariant(&alu->dest.dest, invariants))
+         break;
+
+      alu->exact = true;
+      nir_foreach_src(instr, add_src_cb, invariants);
+      break;
+   }
+
+   case nir_instr_type_tex: {
+      nir_tex_instr *tex = nir_instr_as_tex(instr);
+      if (dest_is_invariant(&tex->dest, invariants))
+         nir_foreach_src(instr, add_src_cb, invariants);
+      break;
+   }
+
+   case nir_instr_type_intrinsic: {
+      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+      switch (intrin->intrinsic) {
+      case nir_intrinsic_copy_var:
+         /* If the destination is invariant then so is the source */
+         if (var_is_invariant(intrin->variables[0]->var, invariants))
+            add_var(intrin->variables[1]->var, invariants);
+         break;
+
+      case nir_intrinsic_load_var:
+         if (dest_is_invariant(&intrin->dest, invariants))
+            add_var(intrin->variables[0]->var, invariants);
+         break;
+
+      case nir_intrinsic_store_var:
+         if (var_is_invariant(intrin->variables[0]->var, invariants))
+            add_src(&intrin->src[0], invariants);
+         break;
+
+      default:
+         /* Nothing to do */
+         break;
+      }
+   }
+
+   case nir_instr_type_jump:
+   case nir_instr_type_ssa_undef:
+   case nir_instr_type_load_const:
+      break; /* Nothing to do */
+
+   case nir_instr_type_phi: {
+      nir_phi_instr *phi = nir_instr_as_phi(instr);
+      if (!dest_is_invariant(&phi->dest, invariants))
+         break;
+
+      nir_foreach_phi_src(src, phi) {
+         add_src(&src->src, invariants);
+         add_cf_node(&src->pred->cf_node, invariants);
+      }
+      break;
+   }
+
+   case nir_instr_type_call:
+      unreachable("This pass must be run after function inlining");
+
+   case nir_instr_type_parallel_copy:
+   default:
+      unreachable("Cannot have this instruction type");
+   }
+}
+
+static bool
+propagate_invariant_impl(nir_function_impl *impl, struct set *invariants)
+{
+   bool progress = false;
+
+   while (true) {
+      uint32_t prev_entries = invariants->entries;
+
+      nir_foreach_block_reverse(block, impl) {
+         nir_foreach_instr_reverse(instr, block)
+            propagate_invariant_instr(instr, invariants);
+      }
+
+      /* Keep running until we make no more progress. */
+      if (invariants->entries > prev_entries) {
+         progress = true;
+         continue;
+      } else {
+         break;
+      }
+   }
+
+   if (progress) {
+      nir_metadata_preserve(impl, nir_metadata_block_index |
+                                  nir_metadata_dominance |
+                                  nir_metadata_live_ssa_defs);
+   }
+
+   return progress;
+}
+
+bool
+nir_propagate_invariant(nir_shader *shader)
+{
+   /* Hash set of invariant things */
+   struct set *invariants = _mesa_set_create(NULL, _mesa_hash_pointer,
+                                             _mesa_key_pointer_equal);
+
+   bool progress = false;
+   nir_foreach_function(function, shader) {
+      if (function->impl && propagate_invariant_impl(function->impl, invariants))
+         progress = true;
+   }
+
+   _mesa_set_destroy(invariants, NULL);
+
+   return progress;
+}