[Mesa-dev] [PATCH] glsl: Eliminate unused built-in variables after compilation

Ian Romanick idr at freedesktop.org
Thu May 29 14:37:34 PDT 2014


From: Ian Romanick <ian.d.romanick at intel.com>

After compilation (and before linking) we can eliminate quite a few
built-in variables.  Basically, any uniform or constant (e.g.,
gl_MaxVertexTextureImageUnits) that isn't used (with one exception) can
be eliminated.  System values, vertex shader inputs (with one
exception), and fragment shader outputs that are not used and not
re-declared in the shader text can also be removed.

gl_ModelViewProjectMatrix and gl_Vertex are used by the built-in
function ftransform.  There are some complications with eliminating
these variables (see the comment in the patch), so they are not
eliminated.

Reduces the peak ir_variable memory usage in a trimmed apitrace of dota2
by 3.5MB on 64-bit.

Before: IR MEM: variable usage / name / total: 5327760 894914 6222674
After:  IR MEM: variable usage / name / total: 2156568 318192 2474760

Reduces the peak ir_variable memory usage in a trimmed apitrace of dota2
by 2.8MB on 32-bit.

Before: IR MEM: variable usage / name / total: 4118280 644100 4762380
After:  IR MEM: variable usage / name / total: 1473408 256871 1730279

v2: Don't remove any built-in with Transpose in the name.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Suggested-by: Eric Anholt <eric at anholt.net>
Cc: Eric Anholt <eric at anholt.net>
Cc: Tapani Pälli <tapani.palli at intel.com>
Cc: Eero Tamminen <eero.t.tamminen at intel.com>
---
After my last edit, I re-ran piglit, re-ran the apitrace, and did 'git
commit --amend' instead of 'git commit --amend -a'. :(

 src/glsl/Makefile.sources               |  1 +
 src/glsl/glsl_parser_extras.cpp         | 20 ++++++++
 src/glsl/ir_optimization.h              |  2 +
 src/glsl/opt_dead_builtin_variables.cpp | 83 +++++++++++++++++++++++++++++++++
 4 files changed, 106 insertions(+)
 create mode 100644 src/glsl/opt_dead_builtin_variables.cpp

diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index 6e230f7..a733323 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -88,6 +88,7 @@ LIBGLSL_FILES = \
 	$(GLSL_SRCDIR)/opt_copy_propagation.cpp \
 	$(GLSL_SRCDIR)/opt_copy_propagation_elements.cpp \
 	$(GLSL_SRCDIR)/opt_cse.cpp \
+	$(GLSL_SRCDIR)/opt_dead_builtin_variables.cpp \
 	$(GLSL_SRCDIR)/opt_dead_builtin_varyings.cpp \
 	$(GLSL_SRCDIR)/opt_dead_code.cpp \
 	$(GLSL_SRCDIR)/opt_dead_code_local.cpp \
diff --git a/src/glsl/glsl_parser_extras.cpp b/src/glsl/glsl_parser_extras.cpp
index d3339e7..323cb23 100644
--- a/src/glsl/glsl_parser_extras.cpp
+++ b/src/glsl/glsl_parser_extras.cpp
@@ -1485,6 +1485,26 @@ _mesa_glsl_compile_shader(struct gl_context *ctx, struct gl_shader *shader,
          ;
 
       validate_ir_tree(shader->ir);
+
+      enum ir_variable_mode other;
+      switch (shader->Stage) {
+      case MESA_SHADER_VERTEX:
+         other = ir_var_shader_in;
+         break;
+      case MESA_SHADER_FRAGMENT:
+         other = ir_var_shader_out;
+         break;
+      default:
+         /* Something invalide to ensure optimize_dead_builtin_uniforms
+          * doesn't remove anything other than uniforms or constants.
+          */
+         other = ir_var_mode_count;
+         break;
+      }
+
+      optimize_dead_builtin_variables(shader->ir, other);
+
+      validate_ir_tree(shader->ir);
    }
 
    if (shader->InfoLog)
diff --git a/src/glsl/ir_optimization.h b/src/glsl/ir_optimization.h
index c63921c..2dfd81e 100644
--- a/src/glsl/ir_optimization.h
+++ b/src/glsl/ir_optimization.h
@@ -122,6 +122,8 @@ void lower_named_interface_blocks(void *mem_ctx, gl_shader *shader);
 bool optimize_redundant_jumps(exec_list *instructions);
 bool optimize_split_arrays(exec_list *instructions, bool linked);
 bool lower_offset_arrays(exec_list *instructions);
+void optimize_dead_builtin_variables(exec_list *instructions,
+                                     enum ir_variable_mode other);
 
 ir_rvalue *
 compare_index_block(exec_list *instructions, ir_variable *index,
diff --git a/src/glsl/opt_dead_builtin_variables.cpp b/src/glsl/opt_dead_builtin_variables.cpp
new file mode 100644
index 0000000..afe22f2
--- /dev/null
+++ b/src/glsl/opt_dead_builtin_variables.cpp
@@ -0,0 +1,83 @@
+/*
+ * 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.
+ */
+
+#include "ir.h"
+#include "ir_visitor.h"
+#include "ir_optimization.h"
+
+/**
+ * Pre-linking, optimize unused built-in variables
+ *
+ * Uniforms, constants, system values, inputs (vertex shader only), and
+ * outputs (fragment shader only) that are not used can be removed.
+ */
+void
+optimize_dead_builtin_variables(exec_list *instructions,
+                                enum ir_variable_mode other)
+{
+   foreach_list_safe(n, instructions) {
+      ir_variable *const var = ((ir_instruction *) n)->as_variable();
+
+      if (var == NULL || var->data.used)
+         continue;
+
+      if (var->data.mode != ir_var_uniform
+          && var->data.mode != ir_var_auto
+          && var->data.mode != ir_var_system_value
+          && var->data.mode != other)
+         continue;
+
+      /* So that linker rules can later be enforced, we cannot elimate
+       * variables that were redeclared in the shader code.
+       */
+      if ((var->data.mode == other || var->data.mode == ir_var_system_value)
+          && var->data.how_declared != ir_var_declared_implicitly)
+         continue;
+
+      if (strncmp(var->name, "gl_", 3) != 0)
+         continue;
+
+      /* gl_ModelViewProjectionMatrix and gl_Vertex are special because they
+       * are used by ftransform.  No other built-in variable is used by a
+       * built-in function.  The forward declarations of these variables in
+       * the built-in function shader does not have the "state slot"
+       * information, so removing these variables from the user shader will
+       * cause problems later.
+       *
+       * Matrix uniforms with "Transpose" are not eliminated because there's
+       * an optimization pass that can turn references to the regular matrix
+       * into references to the transpose matrix.  Eliminating the transpose
+       * matrix would cause that pass to generate references to undeclareds
+       * variables (thank you, ir_validate).
+       *
+       * It doesn't seem worth the effort to track when the transpose could be
+       * eliminated (i.e., when the non-transpose was eliminated).
+       */
+      if (strcmp(var->name, "gl_ModelViewProjectionMatrix") == 0
+          || strcmp(var->name, "gl_Vertex") == 0
+          || strstr(var->name, "Transpose") != NULL)
+         continue;
+
+      var->remove();
+   }
+}
-- 
1.8.1.4



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