nir: Add a pass to lower TES patch_vertices intrinsics to a constant.

In Vulkan, we always have both the TCS and TES available in the same
pipeline, so we can simply use the TCS OutputVertices execution mode
value as the TES PatchVertices built-in.

For GLSL, we handle this in the linker.  But we could use this pass
in the case when both TCS and TES are linked together, if we wanted.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/Makefile.sources

@@ -218,6 +218,7 @@ NIR_FILES = \
 	nir/nir_lower_io_to_scalar.c \
 	nir/nir_lower_io_types.c \
 	nir/nir_lower_passthrough_edgeflags.c \
+	nir/nir_lower_patch_vertices.c \
 	nir/nir_lower_phis_to_scalar.c \
 	nir/nir_lower_regs_to_ssa.c \
 	nir/nir_lower_returns.c \

src/compiler/nir/nir.h

@@ -2490,6 +2490,7 @@ void nir_lower_two_sided_color(nir_shader *shader);
 void nir_lower_clamp_color_outputs(nir_shader *shader);
 
 void nir_lower_passthrough_edgeflags(nir_shader *shader);
+void nir_lower_tes_patch_vertices(nir_shader *tes, unsigned patch_vertices);
 
 typedef struct nir_lower_wpos_ytransform_options {
    int state_tokens[5];

src/compiler/nir/nir_lower_patch_vertices.c

@@ -0,0 +1,53 @@
+/*
+ * 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_builder.h"
+
+void
+nir_lower_tes_patch_vertices(nir_shader *tes_nir, unsigned patch_vertices)
+{
+   nir_foreach_function(function, tes_nir) {
+      if (function->impl) {
+         nir_foreach_block(block, function->impl) {
+            nir_builder b;
+            nir_builder_init(&b, function->impl);
+            nir_foreach_instr_safe(instr, block) {
+               if (instr->type == nir_instr_type_intrinsic) {
+                  nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+                  if (intr->intrinsic != nir_intrinsic_load_patch_vertices_in)
+                     continue;
+
+                  b.cursor = nir_before_instr(&intr->instr);
+                  nir_ssa_def *val = nir_imm_int(&b, patch_vertices);
+                  nir_ssa_def_rewrite_uses(&intr->dest.ssa,
+                                           nir_src_for_ssa(val));
+                  nir_instr_remove(instr);
+               }
+            }
+         }
+
+         nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                               nir_metadata_dominance);
+      }
+   }
+}