nir: Add a stripping pass for improved cacheability

Oftentimes various nir shaders after lowering will be the same, or
almost the same. For example, this can happen when the same shader is
linked with different shaders to form different pipelines and
cross-stage optimizations don't kick in to change it. We want to avoid
running the backend twice on these shaders. We were already doing this
with radeonsi, but we were storing a few extra pieces of information
that made this much less effective compared to TGSI. The worse offender
by far was the program name, which caused most of the cache misses. This
pass strips out these pieces of information, controlled by the NIR_STRIP
debug env variable.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/Makefile.sources

@@ -306,6 +306,7 @@ NIR_FILES = \
 	nir/nir_search_helpers.h \
 	nir/nir_serialize.c \
 	nir/nir_serialize.h \
+	nir/nir_strip.c \
 	nir/nir_split_per_member_structs.c \
 	nir/nir_split_var_copies.c \
 	nir/nir_split_vars.c \

src/compiler/nir/meson.build

@@ -189,6 +189,7 @@ files_libnir = files(
   'nir_search_helpers.h',
   'nir_serialize.c',
   'nir_serialize.h',
+  'nir_strip.c',
   'nir_split_per_member_structs.c',
   'nir_split_var_copies.c',
   'nir_split_vars.c',

src/compiler/nir/nir.h

@@ -3378,6 +3378,8 @@ bool nir_opt_undef(nir_shader *shader);
 
 bool nir_opt_conditional_discard(nir_shader *shader);
 
+void nir_strip(nir_shader *shader);
+
 void nir_sweep(nir_shader *shader);
 
 void nir_remap_dual_slot_attributes(nir_shader *shader,

src/compiler/nir/nir_strip.c

@@ -0,0 +1,107 @@
+/*
+ * Copyright © 2019 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"
+#include "util/debug.h"
+
+/* This pass removes information which is only useful for debugging,
+ * making cache hits from similar shaders more likely.
+ */
+
+static void
+strip_variable(nir_variable *var)
+{
+   var->name = NULL;
+
+   if (var->data.mode != nir_var_shader_in &&
+       var->data.mode != nir_var_shader_out) {
+      /* We assume that this is called after nir_lower_io(), at which point
+       * the original user-facing location is irrelevant except for inputs and
+       * outputs.
+       */
+      var->data.location = 0;
+   }
+}
+
+static void
+strip_register(nir_register *reg)
+{
+   reg->name = NULL;
+}
+
+static bool
+strip_def(nir_ssa_def *def, void *_unused)
+{
+   (void) _unused;
+   def->name = NULL;
+   return true;
+}
+
+static void
+strip_impl(nir_function_impl *impl)
+{
+   nir_index_ssa_defs(impl);
+
+   nir_foreach_variable(var, &impl->locals)
+      strip_variable(var);
+   nir_foreach_register(reg, &impl->registers)
+      strip_register(reg);
+   nir_foreach_block(block, impl) {
+      nir_foreach_instr(instr, block) {
+         nir_foreach_ssa_def(instr, strip_def, NULL);
+      }
+   }
+}
+
+void
+nir_strip(nir_shader *shader)
+{
+   static int should_strip = -1;
+   if (should_strip < 0)
+      should_strip = env_var_as_boolean("NIR_STRIP", true);
+   if (!should_strip)
+      return;
+
+   shader->info.name = NULL;
+   shader->info.label = NULL;
+
+   nir_foreach_variable(var, &shader->uniforms)
+      strip_variable(var);
+   nir_foreach_variable(var, &shader->inputs)
+      strip_variable(var);
+   nir_foreach_variable(var, &shader->outputs)
+      strip_variable(var);
+   nir_foreach_variable(var, &shader->system_values)
+      strip_variable(var);
+   nir_foreach_variable(var, &shader->globals)
+      strip_variable(var);
+
+   nir_foreach_register(reg, &shader->registers)
+      strip_register(reg);
+
+   nir_foreach_function(func, shader) {
+      if (func->impl)
+         strip_impl(func->impl);
+   }
+}