[Mesa-dev] [PATCH 1/2] nir: add nir_opt_shrink_load pass

[Samuel Pitoiset]

This is a very simple pass that just shrinks load_push_constant
intrinsics when some components are unused. For now, it can just
shrink vec4 to vec3, vec3 to vec2 and so on.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
---
 src/compiler/Makefile.sources                   |  1 +
 src/compiler/nir/meson.build                    |  1 +
 src/compiler/nir/nir.h                          |  2 +
 src/compiler/nir/nir_opt_shrink_load_constant.c | 67 +++++++++++++++++++++++++
 4 files changed, 71 insertions(+)
 create mode 100644 src/compiler/nir/nir_opt_shrink_load_constant.c

diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index d3f746f5f9..84dbc26d19 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -268,6 +268,7 @@ NIR_FILES = \
 	nir/nir_opt_move_comparisons.c \
 	nir/nir_opt_peephole_select.c \
 	nir/nir_opt_remove_phis.c \
+	nir/nir_opt_shrink_load.c \
 	nir/nir_opt_trivial_continues.c \
 	nir/nir_opt_undef.c \
 	nir/nir_phi_builder.c \
diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
index b5f27ad667..859a0c1e62 100644
--- a/src/compiler/nir/meson.build
+++ b/src/compiler/nir/meson.build
@@ -162,6 +162,7 @@ files_libnir = files(
   'nir_opt_move_comparisons.c',
   'nir_opt_peephole_select.c',
   'nir_opt_remove_phis.c',
+  'nir_opt_shrink_load.c',
   'nir_opt_trivial_continues.c',
   'nir_opt_undef.c',
   'nir_phi_builder.c',
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 9ab2769e06..5ea8c9926b 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2770,6 +2770,8 @@ bool nir_opt_peephole_select(nir_shader *shader, unsigned limit);
 
 bool nir_opt_remove_phis(nir_shader *shader);
 
+bool nir_opt_shrink_load(nir_shader *shader);
+
 bool nir_opt_trivial_continues(nir_shader *shader);
 
 bool nir_opt_undef(nir_shader *shader);
diff --git a/src/compiler/nir/nir_opt_shrink_load_constant.c b/src/compiler/nir/nir_opt_shrink_load_constant.c
new file mode 100644
index 0000000000..f97b7f9b67
--- /dev/null
+++ b/src/compiler/nir/nir_opt_shrink_load_constant.c
@@ -0,0 +1,67 @@
+/*
+ * Copyright © 2018 Valve 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 bool
+opt_shrink_load(nir_intrinsic_instr *instr)
+{
+   bool progress = false;
+
+   if (instr->intrinsic == nir_intrinsic_load_push_constant) {
+      unsigned mask = nir_ssa_def_components_read(&instr->dest.ssa);
+
+      if (instr->num_components > util_last_bit(mask)) {
+         instr->num_components = util_last_bit(mask);
+         instr->dest.ssa.num_components = instr->num_components;
+         progress = true;
+      }
+   }
+
+   return progress;
+}
+
+bool
+nir_opt_shrink_load(nir_shader *shader)
+{
+   bool progress = false;
+
+   nir_foreach_function(function, shader) {
+      if (!function->impl)
+         continue;
+
+      nir_foreach_block(block, function->impl) {
+         nir_foreach_instr(instr, block) {
+            if (instr->type != nir_instr_type_intrinsic)
+               continue;
+
+            progress |= opt_shrink_load(nir_instr_as_intrinsic(instr));
+         }
+      }
+
+      nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                            nir_metadata_dominance);
+   }
+
+   return progress;
+}
-- 
2.16.1