intel/compiler: Add couple of tests for fs_combine_constants

Add a simple test to kick off the infrastructure.   And also a test
(for now disabled) that fails because the code is returning an
empty shader.  Next patch will fix and enable it.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27131>

src/intel/compiler/meson.build

@@ -200,6 +200,7 @@ if with_tests
         'test_eu_compact.cpp',
         'test_eu_validate.cpp',
         'test_fs_cmod_propagation.cpp',
+        'test_fs_combine_constants.cpp',
         'test_fs_copy_propagation.cpp',
         'test_fs_saturate_propagation.cpp',
         'test_fs_scoreboard.cpp',

src/intel/compiler/test_fs_combine_constants.cpp

@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2024 Intel Corporation
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <gtest/gtest.h>
+#include "brw_fs.h"
+#include "brw_fs_builder.h"
+#include "brw_cfg.h"
+
+using namespace brw;
+
+struct FSCombineConstantsTest : public ::testing::Test {
+   FSCombineConstantsTest() {
+      mem_ctx = ralloc_context(NULL);
+
+      devinfo = {};
+      devinfo.ver = 9;
+      devinfo.verx10 = 90;
+
+      compiler = {};
+      compiler.devinfo = &devinfo;
+      brw_init_isa_info(&compiler.isa, &devinfo);
+
+      params = {};
+      params.mem_ctx = mem_ctx;
+
+      prog_data = {};
+      nir_shader *nir =
+         nir_shader_create(mem_ctx, MESA_SHADER_COMPUTE, NULL, NULL);
+
+      shader = new fs_visitor(&compiler, &params, NULL,
+                              &prog_data.base, nir, 8, false, false);
+   }
+
+   ~FSCombineConstantsTest() override {
+      delete shader;
+      ralloc_free(mem_ctx);
+      mem_ctx = NULL;
+   }
+
+   void *mem_ctx;
+   brw_compiler compiler;
+   brw_compile_params params;
+   intel_device_info devinfo;
+   struct brw_wm_prog_data prog_data;
+   struct gl_shader_program *shader_prog;
+
+   fs_visitor *shader;
+
+   bool opt_combine_constants(fs_visitor *s) {
+      const bool print = getenv("TEST_DEBUG");
+
+      if (print) {
+         fprintf(stderr, "= Before =\n");
+         s->cfg->dump();
+      }
+
+      bool ret = s->opt_combine_constants();
+
+      if (print) {
+         fprintf(stderr, "\n= After =\n");
+         s->cfg->dump();
+      }
+
+      return ret;
+   }
+};
+
+static fs_builder
+make_builder(fs_visitor *s)
+{
+   return fs_builder(s, s->dispatch_width).at_end();
+}
+
+TEST_F(FSCombineConstantsTest, Simple)
+{
+   fs_builder bld = make_builder(shader);
+
+   fs_reg r = brw_vec8_grf(1, 0);
+   fs_reg imm_a = brw_imm_ud(1);
+   fs_reg imm_b = brw_imm_ud(2);
+
+   bld.SEL(r, imm_a, imm_b);
+   shader->calculate_cfg();
+
+   bool progress = opt_combine_constants(shader);
+   ASSERT_TRUE(progress);
+
+   ASSERT_EQ(shader->cfg->num_blocks, 1);
+   bblock_t *block = cfg_first_block(shader->cfg);
+   ASSERT_NE(block, nullptr);
+
+   /* We can do better but for now sanity check that
+    * there's a MOV and a SEL.
+    */
+   ASSERT_EQ(bblock_start(block)->opcode, BRW_OPCODE_MOV);
+   ASSERT_EQ(bblock_end(block)->opcode, BRW_OPCODE_SEL);
+}
+
+TEST_F(FSCombineConstantsTest, DISABLED_DoContainingDo)
+{
+   fs_builder bld = make_builder(shader);
+
+   fs_reg r1 = brw_vec8_grf(1, 0);
+   fs_reg r2 = brw_vec8_grf(2, 0);
+   fs_reg imm_a = brw_imm_ud(1);
+   fs_reg imm_b = brw_imm_ud(2);
+
+   bld.DO();
+   bld.DO();
+   bld.SEL(r1, imm_a, imm_b);
+   bld.WHILE();
+   bld.WHILE();
+   bld.SEL(r2, imm_a, imm_b);
+   shader->calculate_cfg();
+
+   unsigned original_num_blocks = shader->cfg->num_blocks;
+
+   bool progress = opt_combine_constants(shader);
+   ASSERT_TRUE(progress);
+
+   /* We can do better but for now sanity check there's
+    * enough blocks, since the original issue motivating this
+    * test is that the shader would be empty.
+    */
+   ASSERT_GE(shader->cfg->num_blocks, original_num_blocks);
+   shader->validate();
+}
+