nir: add an optimization to turn global registers into local registers

After linking and inlining, this allows us to convert these registers
into SSA values and optimise more code.

3 files changed, 106 insertions, 0 deletions

diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index 27b4da17034..6bc7cd7cd38 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -24,6 +24,7 @@ NIR_FILES = \
 	$(GLSL_SRCDIR)/nir/nir_lower_variables_scalar.c \
 	$(GLSL_SRCDIR)/nir/nir_opcodes.c \
 	$(GLSL_SRCDIR)/nir/nir_opcodes.h \
+	$(GLSL_SRCDIR)/nir/nir_opt_global_to_local.c \
 	$(GLSL_SRCDIR)/nir/nir_print.c \
 	$(GLSL_SRCDIR)/nir/nir_remove_dead_variables.c \
 	$(GLSL_SRCDIR)/nir/nir_validate.c \
diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index e14c9d1fcea..7d55948ab86 100644
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1263,6 +1263,8 @@ void nir_lower_system_values(nir_shader *shader);
 
 void nir_lower_atomics(nir_shader *shader);
 
+bool nir_opt_global_to_local(nir_shader *shader);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/src/glsl/nir/nir_opt_global_to_local.c b/src/glsl/nir/nir_opt_global_to_local.c
new file mode 100644
index 00000000000..00db37ba79d
--- /dev/null
+++ b/src/glsl/nir/nir_opt_global_to_local.c
@@ -0,0 +1,103 @@
+/*
+ * 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:
+ *    Connor Abbott ([email protected])
+ *
+ */
+
+#include "nir.h"
+
+static bool
+global_to_local(nir_register *reg)
+{
+   nir_function_impl *impl = NULL;
+
+   assert(reg->is_global);
+
+   struct set_entry *entry;
+   set_foreach(reg->defs, entry) {
+      nir_instr *instr = (nir_instr *) entry->key;
+      nir_function_impl *instr_impl =
+         nir_cf_node_get_function(&instr->block->cf_node);
+      if (impl != NULL) {
+         if (impl != instr_impl)
+            return false;
+      } else {
+         impl = instr_impl;
+      }
+   }
+
+   set_foreach(reg->uses, entry) {
+      nir_instr *instr = (nir_instr *) entry->key;
+      nir_function_impl *instr_impl =
+         nir_cf_node_get_function(&instr->block->cf_node);
+      if (impl != NULL) {
+         if (impl != instr_impl)
+            return false;
+      } else {
+         impl = instr_impl;
+      }
+   }
+
+   set_foreach(reg->if_uses, entry) {
+      nir_if *if_stmt = (nir_if *) entry->key;
+      nir_function_impl *if_impl = nir_cf_node_get_function(&if_stmt->cf_node);
+      if (impl != NULL) {
+         if (impl != if_impl)
+            return false;
+      } else {
+         impl = if_impl;
+      }
+   }
+
+   if (impl == NULL) {
+      /* this instruction is never used/defined, delete it */
+      nir_reg_remove(reg);
+      return true;
+   }
+
+   /*
+    * if we've gotten to this point, the register is always used/defined in
+    * the same implementation so we can move it to be local to that
+    * implementation.
+    */
+
+   exec_node_remove(&reg->node);
+   exec_list_push_tail(&impl->registers, &reg->node);
+   reg->index = impl->reg_alloc++;
+   reg->is_global = false;
+   return true;
+}
+
+bool
+nir_opt_global_to_local(nir_shader *shader)
+{
+   bool progress = false;
+
+   foreach_list_typed_safe(nir_register, reg, node, &shader->registers) {
+      if (global_to_local(reg))
+         progress = true;
+   }
+
+   return progress;
+}