panfrost/midgard: Flush undefineds to zero

Fixes a buggy dEQP test.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>

src/gallium/drivers/panfrost/ci/expected-failures.txt

@@ -256,12 +256,6 @@ dEQP-GLES2.functional.rasterization.limits.points
 dEQP-GLES2.functional.shaders.builtin_variable.fragcoord_w
 dEQP-GLES2.functional.shaders.preprocessor.predefined_macros.line_2_fragment
 dEQP-GLES2.functional.shaders.preprocessor.predefined_macros.line_2_vertex
-dEQP-GLES2.functional.shaders.random.all_features.fragment.0
-dEQP-GLES2.functional.shaders.random.all_features.fragment.16
-dEQP-GLES2.functional.shaders.random.all_features.fragment.5
-dEQP-GLES2.functional.shaders.random.all_features.fragment.6
-dEQP-GLES2.functional.shaders.random.all_features.vertex.0
-dEQP-GLES2.functional.shaders.random.all_features.vertex.17
 dEQP-GLES2.functional.shaders.scoping.valid.local_variable_hides_function_parameter_fragment
 dEQP-GLES2.functional.shaders.scoping.valid.local_variable_hides_function_parameter_vertex
 dEQP-GLES2.functional.shaders.struct.local.dynamic_loop_assignment_fragment

src/gallium/drivers/panfrost/meson.build

@@ -36,6 +36,7 @@ files_panfrost = files(
   'midgard/midgard_liveness.c',
   'midgard/midgard_ops.c',
 
+  'midgard/nir_undef_to_zero.c',
   'midgard/nir_lower_blend.c',
   'midgard/nir_lower_framebuffer.c',
   'midgard/cppwrap.cpp',

src/gallium/drivers/panfrost/midgard/compiler.h

@@ -444,4 +444,10 @@ void emit_binary_bundle(
                 midgard_bundle *bundle,
                 struct util_dynarray *emission,
                 int next_tag);
+
+/* NIR stuff */
+
+bool
+nir_undef_to_zero(nir_shader *shader);
+
 #endif

src/gallium/drivers/panfrost/midgard/midgard_compile.c

@@ -404,6 +404,8 @@ midgard_nir_lower_fdot2(nir_shader *shader)
         return progress;
 }
 
+/* Flushes undefined values to zero */
+
 static void
 optimise_nir(nir_shader *nir)
 {
@@ -464,6 +466,8 @@ optimise_nir(nir_shader *nir)
                 }
 
                 NIR_PASS(progress, nir, nir_opt_undef);
+                NIR_PASS(progress, nir, nir_undef_to_zero);
+
                 NIR_PASS(progress, nir, nir_opt_loop_unroll,
                          nir_var_shader_in |
                          nir_var_shader_out |

src/gallium/drivers/panfrost/midgard/nir_undef_to_zero.c

@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2019 Collabora, Ltd.
+ *
+ * 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.
+ *
+ * Authors (Collabora):
+ *   Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
+ */
+
+/**
+ * @file
+ *
+ * Flushes undefined SSA values to a zero vector fo the appropriate component
+ * count, to avoid undefined behaviour in the resulting shader. Not required
+ * for conformance as use of uninitialized variables is explicitly left
+ * undefined by the spec.  Works around buggy apps, however.
+ *
+ * Call immediately after nir_opt_undef. If called before, larger optimization
+ * opportunities from the former pass will be missed. If called outside of an
+ * optimization loop, constant propagation and algebraic optimizations won't be
+ * able to kick in to reduce stuff consuming the zero.
+ */
+
+#include "compiler/nir/nir.h"
+#include "compiler/nir/nir_builder.h"
+
+bool nir_undef_to_zero(nir_shader *shader);
+
+bool
+nir_undef_to_zero(nir_shader *shader)
+{
+        bool progress = false;
+
+        nir_foreach_function(function, shader) {
+                if (!function->impl) continue;
+
+                nir_builder b;
+                nir_builder_init(&b, function->impl);
+
+                nir_foreach_block(block, function->impl) {
+                        nir_foreach_instr_safe(instr, block) {
+                                if (instr->type != nir_instr_type_ssa_undef) continue;
+
+                                nir_ssa_undef_instr *und = nir_instr_as_ssa_undef(instr);
+
+                                /* Get the required size */
+                                unsigned c = und->def.num_components;
+                                unsigned s = und->def.bit_size;
+
+                                nir_const_value v[16];
+                                assert(c <= 16);
+
+                                memset(v, 0, sizeof(v));
+
+                                b.cursor = nir_before_instr(instr);
+                                nir_ssa_def *zero = nir_build_imm(&b, c, s, v);
+                                nir_src zerosrc = nir_src_for_ssa(zero);
+
+                                nir_ssa_def_rewrite_uses(&und->def, zerosrc);
+
+                                progress |= true;
+                        }
+                }
+
+                nir_metadata_preserve(function->impl, nir_metadata_block_index | nir_metadata_dominance);
+
+        }
+
+        return progress;
+}
+
+