nir: Move nir_lower_mediump_outputs from ir3

(Original code from ir3)

Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4716>

src/compiler/Makefile.sources

@@ -271,6 +271,7 @@ NIR_FILES = \
 	nir/nir_lower_io_to_temporaries.c \
 	nir/nir_lower_io_to_scalar.c \
 	nir/nir_lower_io_to_vector.c \
+	nir/nir_lower_mediump_outputs.c \
 	nir/nir_lower_non_uniform_access.c \
 	nir/nir_lower_packing.c \
 	nir/nir_lower_passthrough_edgeflags.c \

src/compiler/nir/meson.build

@@ -150,6 +150,7 @@ files_libnir = files(
   'nir_lower_io_to_temporaries.c',
   'nir_lower_io_to_scalar.c',
   'nir_lower_io_to_vector.c',
+  'nir_lower_mediump_outputs.c',
   'nir_lower_non_uniform_access.c',
   'nir_lower_packing.c',
   'nir_lower_passthrough_edgeflags.c',

src/compiler/nir/nir.h

@@ -4278,6 +4278,8 @@ bool nir_lower_doubles(nir_shader *shader, const nir_shader *softfp64,
                        nir_lower_doubles_options options);
 bool nir_lower_pack(nir_shader *shader);
 
+void nir_lower_mediump_outputs(nir_shader *nir);
+
 bool nir_lower_point_size(nir_shader *shader, float min, float max);
 
 typedef enum {

src/compiler/nir/nir_lower_mediump_outputs.c

@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2020 Google, 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.
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+/* Lower mediump FS outputs to fp16 */
+
+static bool
+lower_output_var(nir_shader *nir, int location)
+{
+   nir_foreach_variable (var, &nir->outputs) {
+      if (var->data.driver_location == location &&
+            ((var->data.precision == GLSL_PRECISION_MEDIUM) ||
+             (var->data.precision == GLSL_PRECISION_LOW))) {
+         if (glsl_get_base_type(var->type) == GLSL_TYPE_FLOAT)
+            var->type = glsl_float16_type(var->type);
+         
+         return glsl_get_base_type(var->type) == GLSL_TYPE_FLOAT16;
+      }
+   }
+
+   return false;
+}
+
+void
+nir_lower_mediump_outputs(nir_shader *nir)
+{
+   nir_function_impl *impl = nir_shader_get_entrypoint(nir);
+   assert(impl);
+
+   /* Get rid of old derefs before we change the types of the variables */
+   nir_opt_dce(nir);
+
+   nir_builder b;
+   nir_builder_init(&b, impl);
+
+   nir_foreach_block_safe (block, impl) {
+      nir_foreach_instr_safe (instr, block) {
+         if (instr->type != nir_instr_type_intrinsic)
+            continue;
+
+         nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+         if (intr->intrinsic != nir_intrinsic_store_output)
+            continue;
+
+         if (!lower_output_var(nir, nir_intrinsic_base(intr)))
+            continue;
+
+         b.cursor = nir_before_instr(&intr->instr);
+         nir_instr_rewrite_src(&intr->instr, &intr->src[0],
+         nir_src_for_ssa(nir_f2f16(&b, intr->src[0].ssa)));
+
+         nir_intrinsic_set_type(intr, nir_type_float16);
+      }
+   }
+}