nir/tests: add DCE test for loops following a jump

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10284>

src/compiler/nir/meson.build

@@ -421,4 +421,17 @@ if with_tests
     should_fail : meson.get_cross_property('xfail', '').contains('load_store_vectorizer'),
     protocol : gtest_test_protocol,
   )
+
+  test(
+    'nir_opt_dce',
+    executable(
+      'nir_opt_dce_tests',
+      files('tests/dce_tests.cpp'),
+      cpp_args : [cpp_msvc_compat_args],
+      gnu_symbol_visibility : 'hidden',
+      include_directories : [inc_include, inc_src, inc_mapi, inc_mesa, inc_gallium, inc_gallium_aux],
+      dependencies : [dep_thread, idep_gtest, idep_nir, idep_mesautil],
+    ),
+    suite : ['compiler', 'nir'],
+  )
 endif

src/compiler/nir/tests/dce_tests.cpp

@@ -0,0 +1,105 @@
+/*
+ * Copyright © 2020 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 <gtest/gtest.h>
+#include "nir.h"
+#include "nir_builder.h"
+
+class nir_opt_dce_test : public ::testing::Test {
+protected:
+   nir_opt_dce_test();
+   ~nir_opt_dce_test();
+
+   nir_builder bld;
+};
+
+nir_opt_dce_test::nir_opt_dce_test()
+{
+   glsl_type_singleton_init_or_ref();
+
+   static const nir_shader_compiler_options options = { };
+   bld = nir_builder_init_simple_shader(MESA_SHADER_VERTEX, &options, "dce test");
+}
+
+nir_opt_dce_test::~nir_opt_dce_test()
+{
+   ralloc_free(bld.shader);
+   glsl_type_singleton_decref();
+}
+
+nir_phi_instr *create_one_source_phi(nir_shader *shader, nir_block *pred,
+                                     nir_ssa_def *def)
+{
+   nir_phi_instr *phi = nir_phi_instr_create(shader);
+   nir_phi_instr_add_src(phi, pred, nir_src_for_ssa(def));
+   nir_ssa_dest_init(&phi->instr, &phi->dest,
+                     def->num_components, def->bit_size, NULL);
+
+   return phi;
+}
+
+TEST_F(nir_opt_dce_test, return_before_loop)
+{
+   /* Test that nir_opt_dce() works correctly with loops immediately following a jump.
+    * nir_opt_dce() has a fast path for loops without continues, and this test ensures that it
+    * looks at the actual predecessors of the header instead of just counting.
+    *
+    *  block block_0:
+    *  // preds:
+    *  return
+    *  // succs: block_3
+    *  loop {
+    *     block block_1:
+    *     // preds: block_1
+    *     vec1 32 ssa_1 = phi block_1: ssa_0
+    *     vec1 32 ssa_0 = load_const (0x00000001)
+    *     vec1 32 ssa_2 = deref_var &out (shader_out int) 
+    *     intrinsic store_deref (ssa_2, ssa_1) (1, 0)
+    *     // succs: block_1
+    *  }
+    *  block block_2:
+    *  // preds:
+    *  // succs: block_3
+    *  block block_3:
+    *
+    * If the fast path is taken here, ssa_0 will be incorrectly DCE'd.
+    */
+
+   nir_variable *var = nir_variable_create(bld.shader, nir_var_shader_out, glsl_int_type(), "out");
+
+   nir_jump(&bld, nir_jump_return);
+
+   nir_loop *loop = nir_push_loop(&bld);
+
+   nir_ssa_def *one = nir_imm_int(&bld, 1);
+
+   nir_phi_instr *phi = create_one_source_phi(bld.shader, one->parent_instr->block, one);
+   nir_instr_insert_before_block(one->parent_instr->block, &phi->instr);
+
+   nir_store_var(&bld, var, &phi->dest.ssa, 0x1);
+
+   nir_pop_loop(&bld, loop);
+
+   ASSERT_FALSE(nir_opt_dce(bld.shader));
+
+   nir_validate_shader(bld.shader, NULL);
+}